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--- In ham_amplifiers@..., R L Measures <r@...> wrote:

On Nov 6, 2006, at 7:03 AM, Jan Erik Holm wrote:

I?m working on fixing up a L-4B, it has fried resistors
in the supressors. They use 3 x 15 ohms but I have none
in my junkbox however I have plenty of 10 ohm R?s, will
that do? 3 x 10 ohm R?s?
It doesn?t seem to matter too much, I notice that the L-7
use 2 x 47 ohm R?s and the Henry 3K 2 x 150 ohm R?s, it
seems to be all over the place.

RICH SEZ.... Hello, Jim. == In a VHF parasitic suppressor, when

one sees obliteration, it usually means VHF oscillation.

### No it doesn't. With his 3 x paralled 15 ohm resistor's... it
means he has 5 ohms in total.... and the wrong value to start with !


The goals of a VHF

parasitic suppressor are to build one with a low VHF-Q that won't
melt-down at 29MHz. Typical factory-stock suppressors have a Q of

c.

5 @ 100MHz. However, VHF suppressors can be built with a Q of

1.5.

This Q-decrease decreases VHF gain with the tradeoff of about 2%
power decrease at 29MHz.

### which means the nichrome has to diss 26 watts. The STOCK L4B
suppressor's are bullet proof.... and even more bullet proof, after
u grnd the grids directly to chassis.... like several hundred other
owner's have done. Rich... how many suppressor kits have you
actually sold to L4B owners ??? This is truthfully the very 1st
time in 30 years I have ever heard of anyone frying the suppressor
in a L4B.... or a L4 for that matter. I don't even think it can be
done. Now with just a 5 ohm suppressor... that's a diff story.

I?m following VE7RF?s advice to ground grid pins with
wide straps.

RICH SEZ.. please check grid resonance with a dipmeter before and

after and get back to us with the results.

### Yes, do that.... it might change all of 1 mhz... so what ? At
least it's now more stable...and 25 watts less drive required... and
BETTER IMD..... since the original "NFB" was flawed. The IMD
improves even more... since the xcvr is much cleaner with 20-25
watts less output.

- note - at and above a grounded grid's resonant frequency, the

grid no longer shields the cathode/input from the anode/output.

### That's nice... and totally irrelevant in this case. When the 6
x grid pins are bonded to chassis with short, wide straps.. the
shielding effectiveness of the grid is at absolute MAX.

Suppose I have to put in a fuse in the B-
return to be safe. Also I?m swapping out the .82 R in
the PS for a better glitch R,

good idea. With a sturdy 10?- 20? glitch-R, why use a HV fuse?

### Uh... so u don't have to rely on opening off the ultra SLOW
breakers in the L4PS.... of which mine have never opened in 30
yrs... since the stock .82 ohm 1 w R always beats it to the
punch. You remove the HV fuse.... then install a glitch R.....
the glitch R and 25 uf filter cap in the HV supply will form an
RC network.... dragging out the DURATION of the fault current. All
u end up doing is stressing the stock oem diodes in the HV
supply. That surge rating for diodes is a 1/2 cycle rating... 8.3
Msecs Takes a helluva lot longer than that to open up a slo blo
primary breaker in the 240 line.

also I put diodes across
the I meter.

good move, Jim

### Install RVS connected 1N5408's or better yet. 6A10's..
across BOTH meter's.

Anything else I should think about?

RICH SEZ... lower Q suppressors,

##### Mother Mary... save us all.. from Parasitic hell !!




step-start, high speed switching. 8160
final amplifier?

### 8160 [3x 10] requires a 100 A fil xfmr... which means the fil
xfmr HAS to be mounted AND insulated from the chassis.... and a
bifilar used in the fil xfmr 240 v PRIMARY. Since the fil xfmr is
now in the UNDERSIDE of the RF deck [it's entirely hot with drive
RF]... it just added a TON of un needed extra weight... enough such
that it tips the scales.. and one guy has extreme difficulty getting
the RF deck outa the rack.

### with a 3x 6.... fil xfmr can be 6' away... in lower portion of
Rack.. and cabled with 2 ga flexible wire.. to RF deck. A 80 A
bifilar is a snap.... using paralled 8 ga magnet wire. You can see
pix of that assy on the photo page.

Later... Jim VE7RF

73 Jim SM2EKM




Yahoo! Groups Links

R L Measures, AG6K, 805.386.3734
r@..., , rlm@..., www.somis.org

--- In ham_amplifiers@..., "Robert B. Bonner"
<rbonner@...> wrote:

Jim,

If you think you need a B- fuse, put a 500 ohm 10-25 watt resistor

across the fuse incase it opens.

### IF u install a fuse in the B-.... it's technically a "cathode
fuse"... and a 3agc fuse holder will suffice. Use a 750 ma fast
blow fuse.

## A 500 ohm 10-25 watt resistor across it is a throwback to
Orr's books.["low Z across cathode fuse"] We already tried that on
the 3x6 amp.. and other amps. We removed the 800 ohm 10 watt R...
and replaced it with a 100 K 3 watt MOF. IF Cathode fuse
blows... the V-drop across the 100 k resistor will bias the tubes
to cut off ASAP. Dissipation across the 100 K R is virtually zero
watts.



You should also have a 100-200 Ohm 25 watt B- lead to ground in
the power supply and the 1 ohm grid metering resistor in the head.

### What u just said doesn't make sense at all. Are u saying to
install the 100-200 R between B- and chassis ??? or in series
with B- ??? Both are bad idea's and more throwback's to Orr's
books. IF u install a 100-200 ohm R between B- and chassis....
and say u get a B+ to chassis arc.... fault current could travel
up the 100-200 ohm R..... which makes it now a way too high in
value...."glitch R" ... but only if you fried the 1 ohm grid
shunt..1st.

### If it's just to... "hold the B- close to chassis potential...
and not screw up the metering"... well , the B- is ALREADY at
chassis potentail... via the grid shunt. A better way to do all
this is to just use RVS connected 1N5408's BETWEEN chassis and B-

### This will ensure the B- can never wander more than +/- .7 V
Also, THEN... if u ever get a B+ to chassis arc... fault current
is up one side of the RVS connected diodes... then DIRECTLY to B-
completeing the loop... shorting the HV supply... and the 50 ohm
glitch will limit the Fault current to 53 A.. while the .82 ohm HV
fuse blows asap. [I have NEVER tripped the built in breakers in the
L4PS HV supply. ]





That way things don't "run wild" if the fuse opens.

### Do it with a 100 K across the cathode fuse... and nothing
happens.... just auto shuts down. BUT the CATHODE fuse HAS to
have A resistor across it at all times.... you don't want this
part of the circuit to ever open up... otherwise the cathode will
try and assume full plate V... and stuff like .01 uf bypass caps
between chassis and cold end of fil choke will start exploding.
make sure all the wiring from B-... all the way through to the CT of
the fil xfmr is rock solid.

My large projects have 5 ohm 100 Watt glitch resistors in the PS.

#### 5 ohms is not big enough value to limit current. 4 kv /5 ohms
= 800 A of fault current. 2 A of normal plate current [say a 2 x
8877 amp] thru a 5 ohm glitch will diss just 20 watts.

What's a parasitic suppressor? OH no...

### The stock suppressor in the L4B is fine as is... runs fine
with RTTY /FM/A0/AM on 10M too.

Later... Jim VE7RF

BOB DD

On Nov 6, 2006, at 3:02 PM, ad4hk2004 wrote:

no square in the equation...

C = k * ( area/distance)

As I recall, this is not the equation.

k is the factor for insulator dielectric factor
() is the ratio of the plate area divided by the distance between plates

denny

--- In ham_amplifiers@..., jmltinc@... wrote:

So, is the equation wrong? Jim's answer implies an inverse square

equation.

-J

Yahoo! Groups Links

R L Measures, AG6K, 805.386.3734
r@..., , rlm@..., www.somis.org

--- In ham_amplifiers@..., Jan Erik Holm <sm2ekm@...>
wrote:

I?m working on fixing up a L-4B, it has fried resistors
in the supressors. They use 3 x 15 ohms but I have none
in my junkbox however I have plenty of 10 ohm R?s, will
that do? 3 x 10 ohm R?s?
It doesn?t seem to matter too much, I notice that the L-7
use 2 x 47 ohm R?s

### Whoa.. stop right there. I Don't have the L4B manual handy...
but I'm positive they use 2 x 47 ohm 2 Watt carbon resistors.. and
silver plated strap..... should be same or similar to the L7. I'll
check all 4 x of my L4B's later tonight.



and the Henry 3K 2 x 150 ohm R?s, it

seems to be all over the place.

I?m following VE7RF?s advice to ground grid pins with
wide straps.

#### Originally when I tried this stunt.. I used just one strap ,
from just ONE grid pin PER socket.. [2 x straps in total]. Worked
good... except 10m input swr went nuts. The original idea.. was I
left in the 3 x 200pf caps + choke per socket... so if experiment
bombed... no big deal.. just remove the 2 x straps.

### The 10m high input swr fix was easy.... just REMOVE all 6 x
200pf caps and 2 x chokes... and replace with 3 X wide straps PER
socket...... and keep the coax from xcvr to L4B short. Check and
retweak input swr on all bands if needed. U should be able to get
dead flat input swr. I tweak with top lid off.. on low plate V
cw mode... 600 w into a dummy load... on each band.




Suppose I have to put in a fuse in the B-

return to be safe.

### IF u want a high speed grid fuse.... install a 3agc bayonet
type fuse holder on rear panel. Wire between grid shunt and
chassis. [stock, one end of grid shunt goes to chassis... just open
this point up] Use a 250-350 ma fast fuse.



Also I?m swapping out the .82 R in

the PS for a better glitch R,

#### Whoa. The .82 R 1 watt resistor in the B+ ... IS the HV
fuse .. NOT a glitch R. LEAVE the .82 ohm IN !

### Here's where u install a glitch R in a L4B. Remove the
entire HV interlock assy. It straddles both the top of the
chassis.. and below the chassis. Notice that when u activate the
interlock in slow motion... that the B- lead attached to the HV
interlock below the chassis... grnds out to the chassis.... a split
second before the B+ [attached to top side of chassis
interlock] grnds out to chassis. This was done so B+ will short
[via chassis] DIRECTLY to the B-... blowing the .82 ohm HV fuse.

### IF the HV interlock was just wired to short out the B+ to
chassis.... the path would be through the grid shunt through the
grid meter [if multimeter switched to read Grid I].. then through
the plate current meter... then back to B-... frying both meters and
grid shunt.

### Install REVERSE connected 1N5408's directly between
chassis... and B- Then u will NEVER have the above problem IF
HV shorts to chassis for any reason.

### With the HV interlock removed... we now have room to easily
install the glitch R. Use a 50 ohm 50 watt wire wound
[dale/clarostat/IRC/Ohmite, etc... they all have identical physical
specs]... and mount one end directly to the Millen HV connector.
This glitch R will stand vertical. Top end of resistor will
easily self support itself.. with only the bottom end connected. I
used a internal tooth lockwasher/split ring lockwasher +
flatwasher.. on the Red Millen HV connector.

### Run new 5 kv Belden/similar test prod wire from base of
existing plate choke to TOP of new 50 ohm 50 w glitch R.

### Now... it's bullet proof.



also I put diodes across

the I meter.

### Put REVERSE connected 1N5408's across BOTH meters. [4 in
total.]

Anything else I should think about?

### Yes.... use a separate outboard box.. like a standard
electrical box 8" x 8" x 3-4".... and make a step start delay
for the 240 V line. I used a DPST 30 A P+B relay... to turn on
the 240 V. A 2nd relay..... SPST 30 A P+B relay shorts out
the 25 ohm ...50-100 watt step start resistor. Step start
resistor is simply installed in ONE leg [either leg] of the 240 v
line ..AFTER the 1st relay. Install MOV's across all relay
contacts. My 25 ohm 100 w ww is on standoffs. A better R is to
use a METAL finned dale, etc, R... and bolt directly to sidewall of
box.

### I hardwired the incoming [fused or breaker] 240 V line directly
to the 1st relay [dpst]. Also the L4PS is hardwired to output
side of the step start external box.

### I ran a control cable up to small box on the desk.. with TWO
toggle switches in it. [ 1 x mov across each toggle] Throw
switch 1... and relay 1 operates........ wait 2-4 seconds... throw
switch 2... 2nd relay activates. I used a 1A.. 3gac fuse holder on
the step start box... to feed the control cable. You can get
fancy and use a 2-5 second timer if u want. The built in rocker
switches on the L4B RF deck are flaky at best... I just leave em
both on all the time... and use my control box. [tiny mini box]to
turn the amp on/off.

### This step start will step start BOTH the fils AND the HV
supply.. all in one shot.

### Remove the connection BETWEEN the 2 x 50k-50 watt wire
wound's in the HV supply. Those two bleeder's dissipate a total of
75 watts... or 37.5 watts each. .... which is why the HV supply runs
so hot. The eq resistor's across each of the 8 x 200 uf lytics
ate already 100 K 2 watt units..... and all 8 of em are mounted
several inches away from the caps. I replaced all of mine with
Rich's 100 k 3 watt MOF resistors. Funny thing was... after 25
yrs... the original 100 K carbon resistors were still 100 k ohms.

### Now, you would think the no load HV would junp up with out
the 75 watt load from the series 50 K bleeders.... but it doesn't
budge an inch !! Now here's part 2. In series with the old
pair of 50k bleeders was a 7 k 5 watt.. BELOW the chassis.. In the
outboard HV supply. The v drop across this 7 k is +130v... used to
bias the tubes off on RX. .... dumb idea... since the +130v will
eventually burn the center contacts off the 3PDT T/R relay.
Also... when in mid air... the cathode will try and rise to full
plate V. Now, since u disconnected the 2 x WW HV bleeders.. u
no longer have +130 available. Fix is... wire a 100 K 2 watt MOF
in the CT of the Fil xfmr [yellow wire, if I remember correctly]...
and rewire center contacts of 3PDT T/R relay, so u just short
out this 100 k on TX. Bullet proof. ... and now zero heat from
the outboard supply. Note... drake used eq resistor's across each
lytic... AND a pair of series 50 k ww across the B+ and B-

Want more? Replace the 8 x lytics with ones that are 2-3
times the UF. Install ONE RVS connected 1N5408 across each
lytic. As is... when sucking 800 ma of plate current on key
down... u can easuliy see the 3+ % ripple on any monitor scope.
I'd replace all the diodes in the doubler with 1N5408's.

## Change the +27 vdc 1/2 wave rectifier for the T/R relay to a
DOUBLER..... results in +63 vdc. I installed an internal 3agc fuse
holder... in one leg of the sec that feeds the doubler.. with I
think.. a 1 A fuse. Install a 2 watt drop resistor [forget the
value.. think it was 900 ohms] in one leg of T/R relay coil. This
won't give u qsk....;but super fast vox... as it's now sped up..
and u can speed up any open frame mech relay.. the same way u can
with vac relays. Install a rvs connected 1N5408 diode across the
T/R relay coil. Don't install any bleeder across the 2 x lytics
in the new +63 vdc relay supply.... u want max OCV.

## If u want fancy.. and qsk... use a RJ1A on output side.

### also... install 10 x 1N5408's in the CT on perf board.... in
series with the 100 K 2-3 watt MOF RX cut off resistor from
above. Install a 1000-5000 uf 50 V lytic across the ends of the
bias diode string. Drake ran it with no bias.. and idle was 230
ma. With 10 x diodes it's now 100 ma on ssb.. and 40 ma on cw. NO
increase in imd on ssb on either voltage. [eimac 3-500Z.. MU=130]

### The 1000D and 1000MP-MKV handle the +63 vdc just fine. I also
key em with a P+B ODC-3 opto isolator.... +13.8 vdc input @ 12
ma.... output side rated for 200 V @ 1 A CCS. Output side of opto
has built in back emf protection... but use a diode across T/R
relay coil anyway.

### I have 4 of these amps. I can't get em into parasitic osc...
doesn't mnatter what I do.. including changing tubes to brand X.
Have u got the stock 1900/2650 V power supply. That tune cap
will arc at 4 kv. Want more power... get a bigger amp.

### grnd the grids directly.. and drive power drops 22 watts....
which gets negated a bit... if u install the 10 x bias diodes.

Later... Jim VE7RF

73 Jim SM2EKM

no square in the equation...

C = k * ( area/distance)

k is the factor for insulator dielectric factor
() is the ratio of the plate area divided by the distance between plates

denny

--- In ham_amplifiers@..., jmltinc@... wrote:

So, is the equation wrong? Jim's answer implies an inverse square

equation.

-J

On Nov 6, 2006, at 7:03 AM, Jan Erik Holm wrote:

I?m working on fixing up a L-4B, it has fried resistors
in the supressors. They use 3 x 15 ohms but I have none
in my junkbox however I have plenty of 10 ohm R?s, will
that do? 3 x 10 ohm R?s?
It doesn?t seem to matter too much, I notice that the L-7
use 2 x 47 ohm R?s and the Henry 3K 2 x 150 ohm R?s, it
seems to be all over the place.

Hello, Jim. == In a VHF parasitic suppressor, when one sees
obliteration, it usually means VHF oscillation. The goals of a VHF
parasitic suppressor are to build one with a low VHF-Q that won't
melt-down at 29MHz. Typical factory-stock suppressors have a Q of c.
5 @ 100MHz. However, VHF suppressors can be built with a Q of 1.5.
This Q-decrease decreases VHF gain with the tradeoff of about 2%
power decrease at 29MHz.

I?m following VE7RF?s advice to ground grid pins with
wide straps.

please check grid resonance with a dipmeter before and after and get
back to us with the results.

- note - at and above a grounded grid's resonant frequency, the grid
no longer shields the cathode/input from the anode/output.

Suppose I have to put in a fuse in the B-
return to be safe. Also I?m swapping out the .82 R in
the PS for a better glitch R,

good idea. With a sturdy 10Ω- 20Ω glitch-R, why use a HV fuse?

also I put diodes across
the I meter.

good move, Jim

Anything else I should think about?

lower Q suppressors, step-start, high speed switching. 8160 final
amplifier?

73 Jim SM2EKM




Yahoo! Groups Links

R L Measures, AG6K, 805.386.3734
r@..., , rlm@..., www.somis.org

Jim,

If you think you need a B- fuse, put a 500 ohm 10-25 watt resistor across
the fuse incase it opens. You should also have a 100-200 Ohm 25 watt B-
lead to ground in the power supply and the 1 ohm grid metering resistor in
the head. That way things don’t "run wild" if the fuse opens.

My large projects have 5 ohm 100 Watt glitch resistors in the PS.

What's a parasitic suppressor? OH no...

BOB DD

Im working on fixing up a L-4B, it has fried resistors
in the supressors. They use 3 x 15 ohms but I have none
in my junkbox however I have plenty of 10 ohm Rs, will
that do? 3 x 10 ohm Rs?
It doesnt seem to matter too much, I notice that the L-7
use 2 x 47 ohm Rs and the Henry 3K 2 x 150 ohm Rs, it
seems to be all over the place.

Im following VE7RFs advice to ground grid pins with
wide straps. Suppose I have to put in a fuse in the B-
return to be safe. Also Im swapping out the .82 R in
the PS for a better glitch R, also I put diodes across
the I meter.
Anything else I should think about?

73 Jim SM2EKM

Gent's

Check this out..... plus it's an interesting site worth
bookmarking.



Then, after u have added it to ur shopping buggy.... all u gotta do
is get ur local power co to upgrade the pole pig + drop wires in
front of ur home!

A real steal... compared to that $8750.00 Alpha.

I'd suggest using the 7073 vac tap... which will give you 10 kv
dc under load. This is the perfect xfmr ...for a pair of 3CX-
20,000A/C7's. Also suitable for a pair of 4CX-15/20 K's. All those
tubes are rated at 10 kv @ 6 A. Now I'd highly recomend a Buss 10-
kv HV sand-filled fuse [10" long] Dunno about a "glitch
R"...perhaps a paralleled pair of those 50 ohm 1 kw globars [2"diam
x 24" long]


Later.... Jim VE7RF

--- In ham_amplifiers@..., "g0vdz" <g0vdz@...> wrote:

Dear All, I have a Yaesu FL 2100z. I have had it for about 6 months
and all though I do not use it very much it is nice for contests.
I went onto cqww and decided to enter a topband entry. When i fired
up the liner, it would only put out a marginal signal. I.E. 25 watts
in 40 watts out.
I have lifted the lid and the RFC or anode choke looks a bit the
worst for wear. Could this be the cause of the problem. The other
bands seem reansonable. Has anyone had this problem and if so what

was

the problem
Many thanks to all Nigel G0VDZ

## I USED to own a FL-2100B new.. back in 1977. It did not have
160m in it. The xfmr ran hot, with just the fil + fan + hv on.
Turns out they all do. [xfmr was a combo plate xfmr + fil xfmr]

### what do u mean by other bands being reasonable ? You shoud be
able to get an easy 650 w out on all bands.

### sounds like the RFC went up in smoke.... or has shorted turns...
or is partially damaged. IF it works well on the other bands...
there still must be some continuity through it. Wish I had the
2100 Z schematic here. How big is the bypass cap at the base of
the plate choke ?? Would be interesting to know how many uh this
choke is... and whether it has gaps in it... or where they parked the
series resonances.

### How big is the plate tune and load cap ? Are either/both padded
on 160m ?? If either or is padded... via the bandswitch... u may
want to take a look at the bandswitch contacts.

### what is the INPUT swr on 160m ?? What is the INPUT swr on all
other bands ??

### careful with testing it with lids open... the HV interlock will
short out the B+.

## IF the other bands are good... I doubt it is a parasitic
problem... it's narrowed down to one band... 160m. IF the 160m
tuned input is good... and tune/load caps ok... it should work.
Still... if a 160m padder is not engaged... that would kill the power
output right there..... which should NOT imo... damage the plate
choke. The plate choke may just be discoloured.

## You are going to need to go through the schematic.... with
everything switched to 160m.... and trace out the 160m portion in
detail.

Later... Jim VE7RF

The 350 V rating on 3 watt 100 k MOF resistor's on digikey's
site does not indicate if this is ac or dc.. I'm assuming it's
AC RMS.... if so... the DC V rating should be 495 V ???

On a similar note check out NTE brand of MOF resistors available
in only 2% tolerance for their 2 watt units..... and 5% tol for
their 3 watt units. The 2 watt resistor's are rated at 500
V.... and their 3 watt resistor's are rated at 750 v. Again,
they don't say either... so I'm assuming AC RMS.... so add 41% for
DCV.

in Bloomfield NJ

BTW... I measured a bunch of new NTE 2% 2 watt 1 meg resistor's
for the 1st time last night.... they were all within just .1%
tolerance.. [ 1/10 of one percent] on the low side.

I'd like to know how good the tol actually is on their 3 watt 5%
units. [750 v rated]

later... Jim VE7RF

--- In ham_amplifiers@..., R L Measures <r@...> wrote:

### Why install an adjustable wirewound ?? Plane nuts.

RICH SEZ.... It was part of the over-current relay ckt. --

something that thoriated-tungsten filament tubes do not need
because their emissive layer (di-tungsten carbide / W^2C) can not
be damaged by too much cathode current - as is the case with oxide
cathode tubes such as the 8877.

### Apples and oranges. The 25 ohm 25 watts wire wound R in the
B- lead is fixed..NOT adjustable. It IS the glitch R. The
variable one you are refering to is I believe, part of the FIL
step start ckt. I believe the slider is also used to set the
correct fil V... so they can kill 2 x birds at once.

Try
this for an experiment... if u are brave enough. Install a 25

ohm-

25 watt wire wound wound... in a metal bomb proof box... fed
with 10 kv Red /Black Belden HV wire.... Hook the other

ends of

the HV wire DIRECTLY to the B+ and B- of ur favourite HV
supply..... like a 3-K, etc....[NO HV fuse installed] Install

a

heavy duty vac relay or better yet.. a vac contactor in the B+
lead. Turn on the HV supply.... stand back... and activate

the

vac relay..... applying 3-8 kv across the glitch R...... then
lemme know IF the glitch R remains intact.

RICH SEZ...

A 25W ww resistor is c. 2" long. 3000v is on the ragged edge of

too

much V-gradient for a 2" resistor. Since 10w ww resistors are

also

c. 2" long, it would be preferable to series two of them for

glitch

service at 3000v or greater. The ultimate solution is to use a

surge-

rated - in Joules - type resistor. The glitch resistors we

current

supply with our low-Q suppressor retrofit kits are rated at 120J,
which is slightly more than what a SB-220 HV-PS is capable of

during

a serious glitch.

### agreed... or just use a 50 w wirewound.. if it will fit. A
50 ohm -50 w wire wound fits perfectly on the Millen on the L4B RF
deck. The glitch R on the new HV supply under construction
consists of 4 x paralled 275 w, 200 ohm globars. These are the
old CX type... built in the 60's... can't be immersed in oil... and
are 1" diam x 12" long. With A0.. they will dissipate 450
W... so a pair of 6" fans will suck air outa the Separate HV
cab.... everything is positioned in such a fashion so the plate
xfmr and caps and diode board plus glitch R's get cooled.
Each glitch R is mounted on standoffs, horizontal, just behind
front panel... and 4 x high... so they eat up a 6" x 12" space...
hence the 2 x 6" diam fans side by side on front panel. With
speed control... not much noise.

He also smoked the safety diode between chassis and one end

of

the glitch R. He shoulda
also had safety diodes across both the grid + plate meter.

On a

8877... it really needs electronic fast grid overcurrent
protection.....

RICH SEZ.... The problem with 8877s is not grid damage from too
much HF grid-I, it's gold-evaporation from the grid caused by
occasional UHF parasitic oscillations that causes large bursts

of

UHF grid-I that evaporates off thin layers of gold, which in

turn

forms gold melt balls that create leakage paths in the vacuum.

It

is my opinion that the way to stop gold sputtering is to limit

peak

discharge current from the HV filter C with a sturdy glitch R

in the

HV+ lead. As I see it, 8877s have so much UHF gain that they

can be

a pain.

### agreed..... plan B is to use a REAL tube. In fact.. that's
also Plan A.

which I doubt would even work with the safety
diode shorted between chassis and his glitch R/ B-

agreed

### Here's the deal..Now this IS important. . A buddy of mine
brought over a QST article a few yrs back... in the stray's
dept... it depicted ur typ "electronic grid overcurrent"
protection scheme.... seen in many handbook projects... and also
used in many commercially produced linears. In many handbook

amp

designs.... you will see a pair of diodes REVERSE connected...
between the chassis and B- Only one diode is really

needed...

the worse thing that can happen usually.. is a B+ to chassis
short.

RICH SEZ..... which would be the case if the glitch-R was not

capable of limiting I-pk to the diode's peak-current ability. (typ.
200A-pk in 3A diodes or 400A-pk in 6A diodes)

### agreed. 8 kv /50 ohm glitch = 160A Those surge ratings
for diodes are only 1/2 cycle ratings... or just 8.3 msecs. The
100+ uf filter cap's I use, PLUS the 50 ohm glitch R form a RC
network.. dragging out the DURATION of the surge. To avoid
stressing the safety diodes.... I use 2-3 paralleled 6 A
diodes.... + a HV fuse. 160 A will open a HV fuse <2 msecs.
With no HV fuse... you require some big surge rated diodes... and
6 A diodes are dirt cheap..... unless you are Ameritron... and can
only aford one x 1 cent 30 A rated diode.

### The tech note went on to show what really happens... IF
reverse connected diodes are installed from chassis to B- AND
electronic grid protection is used. They re-drew the entire
schematic.... and what is now depicted is the 2nd diode [not
needed].... ends up DIRECTLY in parallel... with.. u guessed

it....

the small value resistor installed between grid shunt and
chassis. This small value resistor, [typ 5-15 ohms] has DC grid
current flowing through it all the time. It also has a V drop
across it.. typ 1-3 volts... which is fed to the wiper of a
pot... used as a V divider... then applied to a transistor...
activates a relay.. etc.. kicks amp offline, lights LED...
latches... etc. Trbl is... If the un needed 2nd safety

diode

is used.... the V drop across the resistor is directly in

parallel

with it... and turns on the diode !!!! DC Grid current is

then

partially or fully diverted through the un-needed safety

diode....

and u guessed it... the dc grid meter is now reading too low !

Rich SEZ...Use a 0.5? grid-current meter shunt-R and one can read

up to 1A of grid-I without exceeding a Si diode's 0.5v threshold
point.

### Apples and oranges. The v drop across the grid shunt was not
the issue. It's the small 5-15 ohm resistor in SERIES with the
shunt.... and the Vdrop across this 5-15 ohms is used for the
electronic grid overcurrent ckt. With the electronic grid
current protection removed... u are only left with the normal tiny
shunt resistance of a typ 0-1000 ma grid meter... which typ
consists of a 50 ohm internal resistance 0-1 ma meter in parallel
with a small value shunt... like .082 ohm.

### The fix is... to remove the un-needed safety diode.

### On my 3000/6000A7 designs... NO electronic grid overcurrent
protection is used.

RICH SEZ... Does the 3cx6000A7 have a gold-plated grid?

### point well taken... no it does not... it's a "real deal 225 W
CCS grid"... the kind that can be used as a dummy load for ur FT-
1000D. I didn't want to mess with oxide tubes with floozy 4
watt grids in em... like 3CX-800A7's. With those kind of tubes you
have two problems.... the fragile grid... AND the oxide cathode.
One too many times with spikes from overshoots from Xvcr's...
and you will eventually fry the oxide cathode's. It's a nice
tube... but for 2-3 of em... they are NOT cost effective. IMO...
3x3 and 3x6/YC-243's are the way to go.... huge bang for the
buck... zero warmup... can be rebuilt countless times.... and
reasonably priced. Both the 3x3 and 3x6 are used in FM
broadcast around the globe. Those tubes will be around for a
LONG time.

A simple fast 3agc fuse is installed
between neg of grid meter and chassis. [with nothing across

the

fuse either].

RICH SEZ... I would put a transient suppressor diode across the
fuse. They are a dollar.

### I'm assuming you mean a MOV ? Why put a MOV across the
fuseholder ??? IF so... what value MOV? 10-50 V ???
The RVS connected 6 A diodes between chassis and B- are
ALREADY in parallel with the grid fuse holder !.... so no MOV is
really required. We also used RVS connected 6A diodes across
both grid + plate meter's.

RVS connected 6 A diodes ARE used [I use 2-3
6A diodes in EACH direction... 4-6 in total].. wired between
chassis and B- I don't install any 10-1000 ohm resistor
between B- and chassis in either RF deck.... OR HV supply.

RICH SEZ... good

The
RVS connected diodes will never allow the B- to float more

than

+/- .7v from chassis potential[grnd]...(grid fuse open). With
the grid fuse intact... the B- ends up at chassis potential
anyway... since the neg of the grid meter is fed via grid

fuse...

to chassis.

### Originally, we installed a 100 K 3 watt resistor across the
grid fuse holder... thinking IF the grid fuse opened up... the V
drop across the 100 k resistor would bias the amp off.... it
doesn't ! With 800 w of drive applied on a 3x6... and the grid
fuse OPEN... all of a sudden you get 60 w reflected power on the
input of the amp [normally zero]... and abt 20% of normal power
output... [2500w instead of normal 12 kw]. We removed the

100 K

resistor... leaving a wide open (if fuse opens up).... and now

with

drive applied.. and an open grid fuse.... u get ZERO watts
output.... and of course... ZERO DC grid current. [desired

effect]


######## Ok, here's what I think happens when a 100 K R is
installed across the grid fuse holder. When Grid fuse blows
open... dc grid I now flows through the 100 K R... and V drop is
applied to the cathode... adding cut-off bias. Trbl is... the v
drop across the 100 K R is also in PARALLEL with the safety
diodes [rvs connected between chassis and B-] The UN-NEEDED
safety diode between chassis and B- will turn ON.... allowing
DC grid current to flow though it! .. and at the same time... the
V drop across the 100 k resistor is adding bias to the
cathode.... it all reach's equilibrium... and what u end up with
is not enough bias added to cut the tube off.... and at the same
time u have an alternate path for DC grid current.

## So it's EITHER remove the un needed safety diode... OR remove
the 100 k resistor across the fuse. I prefer removing the 100 k
resistor. Reason is.. even though the un needed safety diode
isn't needed for normal faults... like B+ to chassis shorts... it's
STILL required to stop the B- from floating more than .7 V from
chassis potential. BTW... the RVS connected diodes between
chassis and B- are STILL in parallel with the grid fuse.... so
a MOV across the grid fuse isn't really required. Some
paralled 6 A diodes with a 800A surge rating will fair better
than any small common MOV anyway.

### The BIG question is.... WHERE the hell does this 800 watts

of

drive end up ??? It's still being fed to cathode. Does it
just sit there and cook the cathode ??

RICH SEZ..... How can you measure P if the input Z goes bananas?

### good point. With a 100 K resistor across the fuse holder... u
have an alternate path for dc grid current vi the un needed
safety diode. You also end up with partial added bias on the
cathode.... so input Z changes.. and reflected power goes up...
and tube can still be driven.

## with the 100 k R removed.... and fuse open.... input Z should
skyrocket.... and IPA should shut down. We will recheck this, and
report back.

## In any event the grid fuse concept works superbly..
everytime. Some reason's for the grid fuse blowing are.. excess
drive with a dead cxr... HV fuse blown... underloading, etc.

I'm

now thinking that since all bugs are out... and all steady state
grid/plate current/ fil V/ plate V measurements have been

done....

.. and now we just pulse tune it... then talk.... OR just dial

up

the vac tune load caps... "by the pre-set numbers".. we can
probably REDUCE the size of the fast grid fuse from the

current

750 Ma... down to something like 400-500 ma.

RICH SEZ.... If it works, why fix it?

### sorta along the same lines as your 1/4 ...1/2 watt 30 ohm
resistor you use as a grid fuse in the SB-220. Some user's have
smoked the 1/4 watt 30 ohm resistor. Dunno how much a SB-220
pulls for normal Grid I.... but on a L4B... on ssb plate V [2500 v
@ 800ma] normal grid I with 110 w of drive is aprx 300 Ma... or
150 ma per tube. 150 ma through a 30 ohm grid resistor = .675 W !!
[on key down A0] On ssb/cw... AFTER pulse tuning up the amp... u
can probably get away with a 1/4 W resistor. Average grid I is
probably 1/2 of keydown grid I... or 75 ma. 75 ma through a 30
ohm resistor = just .167 watt.

### Also.. my scheme of paralleling a PAIR of 50A magnetic-
hydraulic breaker to make one big 100A breaker's works quite
well.... one such assy is installed in EACH leg of the 240V line.
The kicker here is... we removed the tie bar on each assy.

With

steady state dead cxr stuff... all 4 x poles are turned on....

with

ssb.... u can safely shut one pole off per assy. [now it's a 50

A

breaker] THEN.. if something goes amuck... with a lower value
grid fuse.. and pri breaker [ HV fuse remained same value.. 3
A] ... while on ssb.... both the pri breaker and lower valued

grid

fuse will blow even faster.

RICH SEZ.... Is faster better?

### yeah.... faster is always better. It all boils down to duty
cycle.... which is mode dependent. If ur a RTTY/ A0 type.... then
fuse accordingly. If ur a ssb/cw op.... then you can install
smaller sized fuses/breakers. The kicker here is... with rear
panel mounted 3 agc fuse holders... plus a pair of 2-3 pole
breakers on primary 240 v line [with tie bars removed].. it's a
snap to either change the 3agc fuse to any size you want.... or
ditto with the primary breakers. IF the Grid fuse inadvertantly
blows from op error.... no big deal..... 5 seconds to replace it
with a spare.

Later... Jim VE7RF

R L Measures, AG6K, 805.386.3734
r@..., , rlm@, www.somis.org

--- In ham_amplifiers@..., Bill Turner <dezrat@...>
wrote:

Does anyone have any experience with the new Alpha 8100? Pickings

on

the website are pretty slim. The link to the manual is not working

and

all I can find is a one page brochure. Is it in production?

It would appear to be a rehash of the typical 2-tetrode Alpha such

as

the 91b or the 99 with the addition of a serial port for computer
monitoring. Seems pretty pricey at $4850.00 USD for a manual tune

amp.

All comments welcome.

Bill, W6WRT

### It does appear to be a rehash of the 99 Bill. Interesting,
they only ever built 1500 x 87-A's in 15 yrs between 1990
and 2005... 100 per yr. Notice they say vac relayS..plural. My
bitch with the 8100 is.... it only handles 150 w MAX on
bypass.....where as their new 9500 [$8750.00 auto tune 8877] is
rated for 1.5 kw on bypass. The 9500 also sez vac relayS..
plural.

### can u imagine what these amps would cost in Europe....HUGE
BUX. Also notice Alpha will only ship their amps on a PALLET...
in a wooden crate.... via FREIGHT / MOTOR TRUCK....ditto when they
return ur amp from repair.

## Some fellow on ther other reflector had a pair of 87-A's....
sold em both.... he couldn't afford the shipping charges both
ways every time they had a problem.

### $4850.00 is too much bux...for a manual tune amp.... and
$8750.00 for an auto tune 8877 put's me off of auto tune
amps.
Is the 87-A even real auto tune ? Seems to me they just switch
from one pre-set to another... x segments per band. I think the
pre-sets are originally done into a 50 ohm load..... so what
happens if the load changes say on 3850 khz.... cuz u happen to
have 4 x different ant configs... eaxh with a different load Z
presented to the amp ?

### OZ1AAR built a YC-156... used a motor driven version of
the SSON RI-40 roller coil... + 2 x verticaly mounted 10-1000
pf @ 16 kv motor driven jennings vac caps. A stepper motor on
a bandswitch would work as well.... and an external PC ro run
the thing... with phase detector's built into the linear... then
you would have real auto tune.

### For a lot less bux.. and hassle... you can string several
L4B's, and/or mono band amps, etc, nose to tail.. all tuned up on
different bands. I have 3 x L4B's in this config. If one blew
up... I still have two spares ! You can do the same thing with
YC-156's. The next 3x6 I build will handle the full output of
the 3x3 in front of it.... easy to make em handle globs of RF on
bypass... with vac relays on the INPUT side... and RG-
393 /similar coax on the bypass loop.

### I could afford either new Alpha...but I'd get zero
satisfaction from them. For $4850.00... one could build one
helluva big manual tune linear. A NEW 3x6 or YC-243, plus a 253
lb Dahl xfmr is $2500.00 The rest of it is bit's and
pieces....and time. 1/2" cu tubing is still cheap at home
depot. Then u end up with 10 kw out RTTY /12-15 kw pep out
ssb/cw... and zero problems. For something a tad smaller... a NEW
3x3 PLUS a 127 lb Dahl xfmr is $1500.00 [5 kw out RTTY/ssb/cw]

Later... Jim VE7RF

Dear All, I have a Yaesu FL 2100z. I have had it for about 6 months
and all though I do not use it very much it is nice for contests.
I went onto cqww and decided to enter a topband entry. When i fired
up the liner, it would only put out a marginal signal. I.E. 25 watts
in 40 watts out.
I have lifted the lid and the RFC or anode choke looks a bit the
worst for wear. Could this be the cause of the problem. The other
bands seem reansonable. Has anyone had this problem and if so what was
the problem
Many thanks to all Nigel G0VDZ

To all,
Just wanted to introduced myself. I am a budding ham and have passed
element 2 and 3 as to date. Still working on the element 1 exam but
hope to pass it in a couple of weeks. I have all intentions of going
on to extra as soon as I am ready. Which is one reason I am here TO
LEARN!!! I have a background in in computers (system Engineer) grew up
as an electrician doing Commercial work for my fathers company (three
phase hurts BTY). And took a couple of electronics course in high school.
Current station consists of a 897D and a recently acquired Drake
L4-B in mint condition and a Yaseu mobile 2 meter rig. Going to put up
a GR5V inverted V(sp) shortly.
Can't wait to pass the element one so as to get on the HF bands. I
feel like a five year old and my brain is like a sponge, soaking up
all I can! Darn there is some much to learn. Glad I found the group
and look forward to the knowledge that I will learn here!

Sincerely,
K. Shane Boston KI4JCE

Does anyone have any experience with the new Alpha 8100? Pickings on
the website are pretty slim. The link to the manual is not working and
all I can find is a one page brochure. Is it in production?

It would appear to be a rehash of the typical 2-tetrode Alpha such as
the 91b or the 99 with the addition of a serial port for computer
monitoring. Seems pretty pricey at $4850.00 USD for a manual tune amp.

All comments welcome.

Bill, W6WRT

However, during the 9-years when Bill Fisher, W4AN, was among the living, AMPS did a fairly good job of providing a venue where old farts could pass on what we knew to the new crew.
cheerz

On Nov 4, 2006, at 7:23 PM, renn0vati0 wrote:

Good to be HERE.

--- In ham_amplifiers@..., R L Measures <r@...> wrote:

indeed. Byte bye Tom Rauch.

On Sep 14, 2006, at 8:41 AM, k6kwqdm04 wrote:

This is great! No censorship here.

...

R L Measures, AG6K, 805.386.3734
r@..., , rlm@..., www.somis.org

On Nov 5, 2006, at 2:06 AM, pentalab wrote:

--- In ham_amplifiers@..., R L Measures <r@...> wrote:

On Nov 3, 2006, at 5:10 PM, pentalab wrote:

Gent's

Some poor fellow on the 'other' amp reflector smoked the 25

ohm 25

watt wire wound glitch R on his Henry 3K .

What was not mentioned was that Henry installs the glitch R in
the B-..... NOT the B+.... no big deal... cept the glitch R +

all

wiring in/out of the glitch R has to use 10 kv wire.. and
glitch R well insulated from chassis... on stand offs.

RICH SEZ.... Not only that, but the filament transformer must to

be able to withstand the full anode V. This is why Henry Radio
amplifiers need circuit improvements before they are fired up --
sometimes quite literally.

### Point well taken !! I drew it out on paper... ur right...
the fil xfmr will spike to full B+.... with the glitch R.. in
the B- lead. What were these guys thinking ?

They probably weren't.

Easy to fix.

indeed

Another problem is that this particular resistor usually has an
adjustable tap / slider -- and that makes it not suitable for
glitch service.

### Why install an adjustable wirewound ?? Plane nuts.

It was part of the over-current relay ckt. -- something that
thoriated-tungsten filament tubes do not need because their emissive
layer (di-tungsten carbide / W^2C) can not be damaged by too much
cathode current - as is the case with oxide cathode tubes such as the
8877.

Try
this for an experiment... if u are brave enough. Install a 25 ohm-
25 watt wire wound wound... in a metal bomb proof box... fed
with 10 kv Red /Black Belden HV wire.... Hook the other ends of
the HV wire DIRECTLY to the B+ and B- of ur favourite HV
supply..... like a 3-K, etc....[NO HV fuse installed] Install a
heavy duty vac relay or better yet.. a vac contactor in the B+
lead. Turn on the HV supply.... stand back... and activate the
vac relay..... applying 3-8 kv across the glitch R...... then
lemme know IF the glitch R remains intact.

A 25W ww resistor is c. 2" long. 3000v is on the ragged edge of too
much V-gradient for a 2" resistor. Since 10w ww resistors are also
c. 2" long, it would be preferable to series two of them for glitch
service at 3000v or greater. The ultimate solution is to use a surge-
rated - in Joules - type resistor. The glitch resistors we current
supply with our low-Q suppressor retrofit kits are rated at 120J,
which is slightly more than what a SB-220 HV-PS is capable of during
a serious glitch.

He also smoked the safety diode between chassis and one end of
the glitch R. He shoulda
also had safety diodes across both the grid + plate meter. On a
8877... it really needs electronic fast grid overcurrent
protection.....

RICH SEZ.... The problem with 8877s is not grid damage from too
much HF grid-I, it's gold-evaporation from the grid caused by
occasional UHF parasitic oscillations that causes large bursts of
UHF grid-I that evaporates off thin layers of gold, which in turn
forms gold melt balls that create leakage paths in the vacuum. It
is my opinion that the way to stop gold sputtering is to limit peak
discharge current from the HV filter C with a sturdy glitch R in the
HV+ lead. As I see it, 8877s have so much UHF gain that they can be
a pain.

which I doubt would even work with the safety
diode shorted between chassis and his glitch R/ B-

agreed

### Here's the deal..Now this IS important. . A buddy of mine
brought over a QST article a few yrs back... in the stray's
dept... it depicted ur typ "electronic grid overcurrent"
protection scheme.... seen in many handbook projects... and also
used in many commercially produced linears. In many handbook amp
designs.... you will see a pair of diodes REVERSE connected...
between the chassis and B- Only one diode is really needed...
the worse thing that can happen usually.. is a B+ to chassis
short.

... which would be the case if the glitch-R was not capable of
limiting I-pk to the diode's peak-current ability. (typ. 200A-pk in
3A diodes or 400A-pk in 6A diodes)

### The tech note went on to show what really happens... IF
reverse connected diodes are installed from chassis to B- AND
electronic grid protection is used. They re-drew the entire
schematic.... and what is now depicted is the 2nd diode [not
needed].... ends up DIRECTLY in parallel... with.. u guessed it....
the small value resistor installed between grid shunt and
chassis. This small value resistor, [typ 5-15 ohms] has DC grid
current flowing through it all the time. It also has a V drop
across it.. typ 1-3 volts... which is fed to the wiper of a
pot... used as a V divider... then applied to a transistor...
activates a relay.. etc.. kicks amp offline, lights LED...
latches... etc. Trbl is... If the un needed 2nd safety diode
is used.... the V drop across the resistor is directly in parallel
with it... and turns on the diode !!!! DC Grid current is then
partially or fully diverted through the un-needed safety diode....
and u guessed it... the dc grid meter is now reading too low !

Use a 0.5Ω grid-current meter shunt-R and one can read up to 1A of
grid-I without exceeding a Si diode's 0.5v threshold point.

### The fix is... to remove the un-needed safety diode.

### On my 3000/6000A7 designs... NO electronic grid overcurrent
protection is used.

Does the 3cx6000A7 have a gold-plated grid?

A simple fast 3agc fuse is installed
between neg of grid meter and chassis. [with nothing across the
fuse either].

I would put a transient suppressor diode across the fuse. They are <
a dollar.

RVS connected 6 A diodes ARE used [I use 2-3
6A diodes in EACH direction... 4-6 in total].. wired between
chassis and B- I don't install any 10-1000 ohm resistor
between B- and chassis in either RF deck.... OR HV supply.

good

The
RVS connected diodes will never allow the B- to float more than
+/- .7v from chassis potential[grnd]...(grid fuse open). With
the grid fuse intact... the B- ends up at chassis potential
anyway... since the neg of the grid meter is fed via grid fuse...
to chassis.

### Originally, we installed a 100 K 3 watt resistor across the
grid fuse holder... thinking IF the grid fuse opened up... the V
drop across the 100 k resistor would bias the amp off.... it
doesn't ! With 800 w of drive applied on a 3x6... and the grid
fuse OPEN... all of a sudden you get 60 w reflected power on the
input of the amp [normally zero]... and abt 20% of normal power
output... [2500w instead of normal 12 kw]. We removed the 100 K
resistor... leaving a wide open (if fuse opens up).... and now with
drive applied.. and an open grid fuse.... u get ZERO watts
output.... and of course... ZERO DC grid current. [desired effect]

### The BIG question is.... WHERE the hell does this 800 watts of
drive end up ??? It's still being fed to cathode. Does it
just sit there and cook the cathode ??

How can you measure P if the input Z goes bananas?

## In any event the grid fuse concept works superbly..
everytime. Some reason's for the grid fuse blowing are.. excess
drive with a dead cxr... HV fuse blown... underloading, etc. I'm
now thinking that since all bugs are out... and all steady state
grid/plate current/ fil V/ plate V measurements have been done....
.. and now we just pulse tune it... then talk.... OR just dial up
the vac tune load caps... "by the pre-set numbers".. we can
probably REDUCE the size of the fast grid fuse from the current
750 Ma... down to something like 400-500 ma.

If it works, why fix it?

### Also.. my scheme of paralleling a PAIR of 50A magnetic-
hydraulic breaker to make one big 100A breaker's works quite
well.... one such assy is installed in EACH leg of the 240V line.
The kicker here is... we removed the tie bar on each assy. With
steady state dead cxr stuff... all 4 x poles are turned on.... with
ssb.... u can safely shut one pole off per assy. [now it's a 50 A
breaker] THEN.. if something goes amuck... with a lower value
grid fuse.. and pri breaker [ HV fuse remained same value.. 3
A] ... while on ssb.... both the pri breaker and lower valued grid
fuse will blow even faster.

Is faster better?

Later... Jim VE7RF

R L Measures, AG6K, 805.386.3734
r@..., , rlm@..., www.somis.org

Yahoo! Groups Links

R L Measures, AG6K, 805.386.3734
r@..., , rlm@..., www.somis.org

--- In ham_amplifiers@..., "pentalab" <jim.thomson@...>
wrote:

### Here's the deal..Now this IS important. . A buddy of mine
brought over a QST article a few yrs back... in the stray's
dept... it depicted ur typ "electronic grid overcurrent"
protection scheme.... seen in many handbook projects... and also
used in many commercially produced linears. In many handbook amp
designs.... you will see a pair of diodes REVERSE connected...
between the chassis and B- Only one diode is really needed...
the worse thing that can happen usually.. is a B+ to chassis
short.

### The tech note went on to show what really happens... IF
reverse connected diodes are installed from chassis to B- AND
electronic grid protection is used. They re-drew the entire
schematic.... and what is now depicted is the 2nd diode [not
needed].... ends up DIRECTLY in parallel... with.. u guessed

it....

the small value resistor installed between grid shunt and
chassis. This small value resistor, [typ 5-15 ohms] has DC grid
current flowing through it all the time. It also has a V drop
across it.. typ 1-3 volts... which is fed to the wiper of a
pot... used as a V divider... then applied to a transistor...
activates a relay.. etc.. kicks amp offline, lights LED...
latches... etc. Trbl is... If the un needed 2nd safety

diode

is used.... the V drop across the resistor is directly in parallel
with it... and turns on the diode !!!! DC Grid current is then
partially or fully diverted through the un-needed safety

diode....

and u guessed it... the dc grid meter is now reading too low !

### The fix is... to remove the un-needed safety diode.

########### Here's the MISSING note. Even IF the un -needed diode
is removed on an electronic grid over current scheme.... and the
remaining WANTED safety diode [between chassis and B-] ever
shorts out [typ on ALL Ameritron amps..cuz they use TOO small a
surge rated diode], your fancy electronic grid overcurrent
protection scheme is NO longer gonna work until that safety diode
is replaced ! With the diode shorted, the small value drop
resistor that's part of the above mentioned grid overcurrent
scheme... is now directly in parallel with the shorted diode !!
ALL DC grid current will simply flow through the shorted
diode.. through the PLATE meter... back to cathode.

### Wait, it gets worse! With the safety diode shorted
out... the plate and grid meter are now directly in parallel with
each other. The grid meter however, will still have a 5-15 ohm
resistor in it's neg leg... the plate meter does NOT. The Pos
terminals of both meter's are tied together of course..... so plate
meter will now read the SUM of the plate current AND grid
current.

### Left in that above config... the amp will still work... except
the grid meter will not function... and the grid overcurrent will
not function. IF a HV fuse is used.... and say blows at the
same time the safety diode shorts... you are now in bigger trbl !
With drive applied, and NO plate V.... you will send the grid
current into orbit... and with NO functioning grid over current
protection.... u can kiss the tube goodbye.


### On my buddy's Ameritron amps..[he has since gotten rid of
em].... the manual tells you to .. "check for a shorted safety
diode"... "after an event" !! Now if the bozo who designed it had
used a bigger surge rated diode.. and a glitch R... this would never
happen.

### Beware... some pundits on the "other reflector" have
suggested using a standard pre-packaged bridge rectifier 4-25 A
50V diode assy... like the typ sealed type.. with 4 x wires
protruding out.... as a "safety diode". Now this will work....
PROVIDED u strap the TWO AC input's together.... THEN grnd em to
chassis.... and then wire the + output of the rectifier assy...
to the B- of the HV supply. The neg output of the bridge
rectifier assy is NOT used.

#### On the other reflector.. it was stated to simply wire the
AC input's between chassis and B- !! Draw that config out on
paper.. and u will see that u end up with opposing pairs of
diodes.. and the PIV of 2 of the diodes will be exceeded... and
those two diodes will blow clean in 1/2..... leaving two
paralled open circuits... and now an open loop. Unless u got
more safety diodes installed across each meter.. AND 3-4
more...wired in series in the grid overcurrent circuit.... u will
smoke the meter's and the grid overcurrent assy.

### PIV rating for a safety diode is not an issue... it's
strictly the SURGE rating. 6A diodes are cheap... so are
paralled 1N5408's [3A] .

Later... Jim VE7RF

--- In ham_amplifiers@..., R L Measures <r@...> wrote:

On Nov 3, 2006, at 5:10 PM, pentalab wrote:

Gent's

Some poor fellow on the 'other' amp reflector smoked the 25

ohm 25

watt wire wound glitch R on his Henry 3K .

What was not mentioned was that Henry installs the glitch R in
the B-..... NOT the B+.... no big deal... cept the glitch R +

all

wiring in/out of the glitch R has to use 10 kv wire.. and
glitch R well insulated from chassis... on stand offs.

RICH SEZ.... Not only that, but the filament transformer must to

be able to withstand the full anode V. This is why Henry Radio
amplifiers need circuit improvements before they are fired up --
sometimes quite literally.

### Point well taken !! I drew it out on paper... ur right...
the fil xfmr will spike to full B+.... with the glitch R.. in
the B- lead. What were these guys thinking ? Easy to fix.


Another problem is that this particular resistor usually has an
adjustable tap / slider -- and that makes it not suitable for
glitch service.

### Why install an adjustable wirewound ?? Plane nuts. Try
this for an experiment... if u are brave enough. Install a 25 ohm-
25 watt wire wound wound... in a metal bomb proof box... fed
with 10 kv Red /Black Belden HV wire.... Hook the other ends of
the HV wire DIRECTLY to the B+ and B- of ur favourite HV
supply..... like a 3-K, etc....[NO HV fuse installed] Install a
heavy duty vac relay or better yet.. a vac contactor in the B+
lead. Turn on the HV supply.... stand back... and activate the
vac relay..... applying 3-8 kv across the glitch R...... then
lemme know IF the glitch R remains intact.

He also smoked the safety diode between chassis and one end of
the glitch R. He shoulda
also had safety diodes across both the grid + plate meter. On a
8877... it really needs electronic fast grid overcurrent
protection.....

RICH SEZ.... The problem with 8877s is not grid damage from too

much HF grid-I, it's gold-evaporation from the grid caused by
occasional UHF parasitic oscillations that causes large bursts of
UHF grid-I that evaporates off thin layers of gold, which in turn
forms gold melt balls that create leakage paths in the vacuum. It
is my opinion that the way to stop gold sputtering is to limit peak
discharge current from the HV filter C with a sturdy glitch R in the
HV+ lead. As I see it, 8877s have so much UHF gain that they can be
a pain.

which I doubt would even work with the safety
diode shorted between chassis and his glitch R/ B-

agreed

### Here's the deal..Now this IS important. . A buddy of mine
brought over a QST article a few yrs back... in the stray's
dept... it depicted ur typ "electronic grid overcurrent"
protection scheme.... seen in many handbook projects... and also
used in many commercially produced linears. In many handbook amp
designs.... you will see a pair of diodes REVERSE connected...
between the chassis and B- Only one diode is really needed...
the worse thing that can happen usually.. is a B+ to chassis
short.

### The tech note went on to show what really happens... IF
reverse connected diodes are installed from chassis to B- AND
electronic grid protection is used. They re-drew the entire
schematic.... and what is now depicted is the 2nd diode [not
needed].... ends up DIRECTLY in parallel... with.. u guessed it....
the small value resistor installed between grid shunt and
chassis. This small value resistor, [typ 5-15 ohms] has DC grid
current flowing through it all the time. It also has a V drop
across it.. typ 1-3 volts... which is fed to the wiper of a
pot... used as a V divider... then applied to a transistor...
activates a relay.. etc.. kicks amp offline, lights LED...
latches... etc. Trbl is... If the un needed 2nd safety diode
is used.... the V drop across the resistor is directly in parallel
with it... and turns on the diode !!!! DC Grid current is then
partially or fully diverted through the un-needed safety diode....
and u guessed it... the dc grid meter is now reading too low !

### The fix is... to remove the un-needed safety diode.

### On my 3000/6000A7 designs... NO electronic grid overcurrent
protection is used. A simple fast 3agc fuse is installed
between neg of grid meter and chassis. [with nothing across the
fuse either]. RVS connected 6 A diodes ARE used [I use 2-3
6A diodes in EACH direction... 4-6 in total].. wired between
chassis and B- I don't install any 10-1000 ohm resistor
between B- and chassis in either RF deck.... OR HV supply. The
RVS connected diodes will never allow the B- to float more than
+/- .7v from chassis potential[grnd]...(grid fuse open). With
the grid fuse intact... the B- ends up at chassis potential
anyway... since the neg of the grid meter is fed via grid fuse...
to chassis.

### Originally, we installed a 100 K 3 watt resistor across the
grid fuse holder... thinking IF the grid fuse opened up... the V
drop across the 100 k resistor would bias the amp off.... it
doesn't ! With 800 w of drive applied on a 3x6... and the grid
fuse OPEN... all of a sudden you get 60 w reflected power on the
input of the amp [normally zero]... and abt 20% of normal power
output... [2500w instead of normal 12 kw]. We removed the 100 K
resistor... leaving a wide open (if fuse opens up).... and now with
drive applied.. and an open grid fuse.... u get ZERO watts
output.... and of course... ZERO DC grid current. [desired effect]

### The BIG question is.... WHERE the hell does this 800 watts of
drive end up ??? It's still being fed to cathode. Does it
just sit there and cook the cathode ??

## In any event the grid fuse concept works superbly..
everytime. Some reason's for the grid fuse blowing are.. excess
drive with a dead cxr... HV fuse blown... underloading, etc. I'm
now thinking that since all bugs are out... and all steady state
grid/plate current/ fil V/ plate V measurements have been done....
.. and now we just pulse tune it... then talk.... OR just dial up
the vac tune load caps... "by the pre-set numbers".. we can
probably REDUCE the size of the fast grid fuse from the current
750 Ma... down to something like 400-500 ma.

### Also.. my scheme of paralleling a PAIR of 50A magnetic-
hydraulic breaker to make one big 100A breaker's works quite
well.... one such assy is installed in EACH leg of the 240V line.
The kicker here is... we removed the tie bar on each assy. With
steady state dead cxr stuff... all 4 x poles are turned on.... with
ssb.... u can safely shut one pole off per assy. [now it's a 50 A
breaker] THEN.. if something goes amuck... with a lower value
grid fuse.. and pri breaker [ HV fuse remained same value.. 3
A] ... while on ssb.... both the pri breaker and lower valued grid
fuse will blow even faster.

Later... Jim VE7RF

R L Measures, AG6K, 805.386.3734
r@..., , rlm@..., www.somis.org