--- In ham_amplifiers@..., Steven Grant <w4iiv@...>
wrote:

What we are not seeing is when this fuse goes, the tube is already

bad!

### Say what ? What do u mean "the tube is already bad" ? My
buddy has blown the grid fuse about 8 times cuz of misc other
problems. The tube is still pumping out 15 kw. Ditto with the
grid fuses that have blown in my 2 x 3-500Z linears.


### simply change out the grid fuse.. and you are back in business.
[prudent to investigate why the grid fuse blew open in the 1st
place.... which could be anything from having a blown HV fuse
1st... in which case the grid current skyrockets. My buddy had
an arc over on one of his ant's.... took out one of the HV
sandfilled fuses... followed by the grid fuse. Another time, the
grid fuse blew from accidental overdrive.

STEVEN SEZ... What the grid fuse does is protect the filament
transformer IMO

Steven W4IIV

### The grid fuse protects the grid. When the grid fuse
opens... their is NO DC path for DC grid current... tube shuts
down... can't be driven... and zero watts power output.

### simply change out the grid fuse.. and you are back in business !

### There is also NO path for dc grid current to flow back
into the CT of the fil xfmr.... which then feeds the fil.
Extremely high grid current couldn't damage a fil xfmr
anyway. The dc grid current flows into the CT... then splits
left and right... into each side of the fil, [via the bifilar]
The entire secondary.. including the CT... is built like a tank...
typ rated for 21-80 A, depending on tube type.

later... Jim VE7RF

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

RICH SEZ... The 3cx3000A7 has 0.6 pF of feedback C. That's 6x more
than the 8877 and 4x more than a 3-500Z. At its max-f rating of
110MHz, the 3cx3000A7 has an output to input feedback path with
2500-ohms of XC.

### agreed... so what ?? IMO... the grid is better grnded on a
3000A7... than a 3-500Z.


### In MOST cases... on a HB

3000A7... u can just toss the suppressor.

RICH SEZ...... especially if you just love to repair amplifiers.

### Build a 3000A7 linear.. and try it yourself. The one turn
chrome suppressor from the 8-K is essentially doing...nothing.


### I'm convinced... 98% of stability is how well the control
grid is grounded. A 3-500Z has only ONE internal grid pin....

RICH SEZ... It's a 360? cone shaped collet.

#### Which in turn splits into 3 x extremly thin grid pins !
They should just fed 1 x WIDE strap from the cone collet.. down
to the 3 base pins.... ditto with tubes like 811-A's, 572B's, etc.



RICH SEZ...If the 3-pins are grounded directly, the resonance at the
grid is in the 80MHz range. If the 3 grid pins are grounded
through 200pF caps, the grid resonance is in the 80MHz range. In
my experiences it is > better to measure resonance with a dipmeter
than to guess at it.

### Who cares ??? All I know is that when you directly strap all
6 x grid pins, with wide strap, to the chassis, the SB-220, SB-
221, TL-922 become rock stable... with the OEM
suppressor's.......and that's good enough for me. My only guess
as to why it works is perhaps the grids are now really grounded...
which also makes for 20-25 w LESS drive power.

### Now the AL-80BX and Ameritron with the 2 x 3-500Z's do have
the grids directly grnded.... and STILL spit, arc, etc. [the
guys on the east coast em.. the "firecracker's " ]. The AL-80BX
is a poorly built amp imo. My buddy had so much trbl with his
brand new one... he tossed it... and bought a used L4B... I
modified the L4B.. with the usual mods... 100% reliable.

### W8JI once modified a small GG metal triode... improved the
grid grnding... and built the worlds only [as far as I know] 160-
6m linear.... with NO parasitic suppressor !!

RICH SEZ.... So why does the AL-1500 - that he apparently designed -
have a reputation for sudden 8877 failures? As I see it, an
amplifier that appears to be stable during an hour or so of testing
is not guaranteed to be stable in the long run.


### dunno. I do know a lot of amateur's with the AL-1500.... and
they run flawlessly... some pound out 2500 w PEP on ssb.... for
literally 5 hrs every night.... and almost 365 days a yr... for
the last 4 yrs. IMO,Perhaps some simple protection would
help... like adding grid fuses, high speed grid + plate
overcurrent protection.. a FAST HV fuse..a cathode fuse.... and
a real 50 ohm, 50-100 w glitch resistor. Toss in some fast
high swr protection, and also dump the stock mech T/R relay
scheme.. and replace it with a high speed vac relay. Use of a
digital delay for cw + ssb will help immensely..... these
modern xcvr's crank out globs of RF instantly... even if the sped
up vac relay does operate in < 2msec. Also, xcvr's like the
ICOM's.. will have peak overshoots. That's easy to fix......
just use fixed dc volatge.. fed to the ALC jack at all times !

### In any event...in yrs gone by.. I always start with a 50 ohm
globar.... and keep adding turns[ 1 1/2... 2...2 1/2....3]

till the parasitic goes bye bye. If using a real small globar...
and u run outa room.... reduce the width of the strap.


RICH SEZ... Smooth move. Reducing the width of the strap increases
RF- resistance, which lowers the L/R suppressor's VHF-Q, which in
turn lowers VHF gain and reduces the chance of VHF oscillation.

#### Whoa nellie ! Believe me... plan A was to use 1" wide
strap.... which would mean using a 6" long - 150 w CCS globar...
which I didn't have on hand. At 15 kw... on the high bands, the
RF current is just unreal through that suppressor strap !!!



Another way of increasing RF-resistance is to choose a conductor
that is more resistive than copper. Example -- The 8169 /
4cx3000A amplifier at:
appears to have no parasitic suppressor whatsoever, however the
anode to blocking-cap connector strap, as well as the connection to
the Bruene-bridge neutralizing cap is made out of a nickle-
chromium alloy.

### Here's my problem with Nichrome. It GLOWS ORANGE on the
higher bands. It runs so hot... this thermal heat in turn cooks
the plate blockers !!! IMO, nichrome belongs.... in a toaster
oven. Use wide copper strap on globars = zero problems. ANY
SP type Globar will handle 350 deg C heat CCS... and when used
with copper strap... run just fine. Even a big metal
triode/tetrode will never get hotter than 225 deg C.. when maxed
to the peg.

### Stainless steel is bad too... it will turn BLACK.

### Rich, on the high bands, the tube C makes up a huge chunk of
the total C1 tune cap... which means extremely high RF currents on
17-10m......... all flowing through the parasitic strap
material ........which is NO place for nichrome. Rich, when u
finish ur 4 x 10... fire it up.... on 10/12m... with a dead
cxr.... for just a few seconds.... then report back to us. I wanna
know whether the bagel came out right.... or charcoal !



According to (W6HW) - a friend who worked for Collins Radio Co. -
the 30S-1 amplifier used the same technique.

### Called "L-101" on my 30S-1 schematic.

Later...... Jim VE7RF

What we are not seeing is when this fuse goes, the tube is already bad!
What the grid fuse does is protect the filament transformer IMO

Steven W4IIV





At 05:29 AM 10/1/2006, pentalab wrote:

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

On Sep 29, 2006, at 4:53 PM, pentalab wrote:

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

wrote:

RICH SEZ...Now the bad news: Without W8JI, the "recognized
amplifier expert", Charles Thomas Rauch, Jr., and his

statements

such as the laws of AC circuit analysis do not apply to VHF
suppressors; and VHF resonant circuits can't ring, but HF ones

can, things will definitely be less entertaining.

### this is one soap opera I don't wanna ever hear again!

RICH SEZ... Why read it more than once?

### One has to be either a complete nutcase or bored.... to read
thousands of postings on.. "parasites"



RICH SEZ ..before I started the grate parasite debate with Tom I
was warned by a Ham in Manhattan that he wins debates in the eyes
of his groupies by never backing down, even on issues that, to a
RF-savvy person, make him look the clown. In my opinion, this is
probably something he picked up from his father, Charles Thomas
Rauch, Sr. - editorial - If I go to my grave with a bunch of
newbies believing Tom's statement that Ni-Cr alloys have reverse
RF skin-effect, VHF resonances can't ring, et cetera, I will not
be resting in peace and that's for damn sure.

### Any RF software program that contains RF skin effect
analyis... for doz's of different alloys... at any freq will
tell one... in seconds flat.... that NI-CR alloys DON'T have
reverse RF skin effect. Rauch is full of it.... the software
just said so. Gee, that took all of 3 seconds to punch it into
the software analyis.... what's next... how no commercial
manufacturer of SSB gear is even allowed to use 2 x tone tests
for IMD testing anymore ? [ 2 x tone testing is flawed, by
juggling the freq of the tones about... you can easily hit a sweet
spot where IMD drops, in the real world, nobody uses it]



### Rich, I think you are a.. " #5 " on the Energram
personality trait book [#5's love to argue]. Did you get burned
in the high school debating team ??

### The best way to solve parasitic problems in a TL-922 SB-
220/221 is to REMOVE all 6 x 200 pf bylass caps + 2 x RF
chokes from sockets... and toss em !! Strap all 6 x grid
pins to chassis ..with wide strap..... end of problem.

The grid resonance in a stock TL-922 is in the high 80MHz range.

The grid resonance with the grid pins strapped to ground is
typically about 1MHz lower. How does this make the amplifier more
stable at the 120MHz resonance in the anode circuit?

### Well, this IS the $64K question for sure. I don't have a
clue. All I know is... when the 6 x grid pins are strapped
directly to chassis.. with wide strap... on a SB-220/SB-221.. TL-
922... some Henry amps....... they become rock stable.... WITH the
stock OEM parasitic suppressor's !!!

### Step 1 is to strap all 6 x grid pins to chassis. Now...
IF a parasitic still occurs.... THEN add either [a] nichrome....
or [b] add a real suppressor... made from a globar wound with
strap... and just enough turns to kill the parasitic.

### Why anyone would wanna leave in the 6 x 200 pf caps + 2 x
chokes is beyond me. By directly grnding the grids you now [a]
drive the amp with 20-25 watts LESS power on ALL bands or [b]
really drive the crap outa the amp with the SAME drive power as
b4.... and... [c] eliminate all parasitic problems.. and leave in
the stock oem suppressor's ..... and [d] do the 160m mod
easily, since the grids are now bonded to the chassis.....
otherwise you gotta ADD another 1000 pf ..PER socket...plane
nuts.


Jim VE7RF

Rich, AG6K

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

### Not quite. The GRID RING is bonded to the chassis !! This

is not a case like Rich using 1/2 watt resistor's as "grid

fuses"

which WILL leave the grid floating]

RICH SEZ... Tony -- Have you ever blown a grid fusing R and observed
what happens?

### WE are talkin bout a metal triode... complete with either a
socketed grid ring... or a YC-156/YC-243... with a built in grid
ring.... NOT a SB-220... with 1/4 or 1/2 watt 30 ohm resistor's
installed between one grid pin and chassis.

## IF the 30 ohm resistors explode open... tube shuts down....
nothing happens.... except it's now a pain in the butt to
change out the 30 ohm resistor's........ hence a rear panel 3agc
fuse holder... with a fast 3agc grid fuse... installed between
grid shunt and chassis..... takes 4 seconds to replace. In that
above Rich modified SB-220... the grid is left floating in a
vac....which isn't gonna harm anything... and no, the anode is
not gonna arc to a now floating grid... then arc to the
cathode.

73 Jim VE7RF

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

RICH SEZ...When a high-R exists in the cathode circuit, as soon as

a little current begins to flow, the tube cuts off. My modified
SB-220 and TL-922 do this, and if a tube ever happens to short,
nothing is damaged.

#### Partially agreed. When a grid fuse [inserted between
grid meter and chassis... (or between grid shunt and chassis
on a multimeter)... AND the grid fuse is shunted with a 100 K
resistor..... AND the grid fuse opens, one would think the grid
current [600-900 ma on a 6000A7] flowing through the 100 K
resistor would create enough bias to cut off the tube ? It
sorta does..... fact is.... with 800-1000 w of drive..... you
still get 1/4 pwr output . We simply REMOVED the 100 k
resistor across the grid fuse.... and now all is well. Now
when grid fuse blows open...... zero DC grid current.. zero
watts outa the amp. [where the 800+ watts of drive goes is
beyond me. It either stays in the cathode.. or cooks the
grid.... or both ??? ]

### On one of my L4B's a few yrs back [this one was unmodified], It
was still using the +130 V scheme for cut off bias on RX. The
contacts on the 3PDT t/r relay were bad... and the +130 v was
still being applied on TX !! You could STILL get power
output... [now in class C] ! Fix was to replace relay.... then
rewire with a 100 K in the CT.... and relay contacts shunt the
100 K on TX.... end of problem. RL Drake's... and later
Heath's "brilliant idea" of using +130vdc for cutoff bias on
RX... was one of the stupidest moves ever...... 2nd only to
using 6 x 200 pf caps + 2 x rf chokes on the 6 x grid pins !!

### BTW, the 100 w + 1 kw contacts of the bad T/R relay were
perfectly intact. It's the center contact [with the +130 V}
that goes bad eventually. When this center contact is in mid
air... you have opened the cathode up for a split second.... and
the cathode will want to assume full plate V !


RICH SEZ... - note - In a stock SB-220 or 922, a shorted tube can
destroy the filament transformer in short order.

### say what ?? IF the fil xfmr draws too much current on
it's sec,...... the fuse/small breaker on the PRI of the fil
xfmr should blow ! Oh, I forgot.... in it's infinite wisdom...
neither the SB-220 or the Drake L4B even had fil xfmr pri
fuses........ they relied on the ..'big momma' 20 A slow blow ckt
breaker in the 240 V pri!!! Fix... install a fil xfmr primary
fuse.

## The L4B has an extra winding on the fil xfmr ... after being
run through the 1/2 wave rectifier [ one diode, one cap.... how
CHEAP could they have gotten ?] u get +27 vdc... to run the
T/R relay. Fix is.... either change to a FWB..[+27 vdc]... OR
change to a doubler. The doubler will put out +63 vdc.... and a
resistor is simply inserted in one leg of the stock T/R relay's
coil..... and presto.... you have a fast sped up mech stock
relay.... not qsk... but faster VOX. The + 63 vdc ocv can
[and is] be used also for a speed up circuit for a RJ1-A.

## Either way... this extra smaller sec... used for the T/R
relay... should be FUSED. Fix... install a 3agc fuse holder...
with the appropriate sized fuse. .... end of problems.... like as
in this small sec ever shorted out..... you don't melt the
fil xfmr [ "fused" with a 20 A breaker in the 240 V pri]




RICH SEZ... With 3-500Zs, 1k-ohm will limit anode current to about
25mA when the fuse opens.

### when WHAT fuse blows? A cathode fuse ? If so, I
agree.... and it should be increased to a 20-100 K unit..and
complete cut off will /shoiuld occur.


RICH SEZ - A 250v-rated fuse in a circuit operated by 3000v is not
good engineering practice.

### the 250 V rated cathode fuse is NEVER gonna see 3000 V
across it... and here's why. The worst case senario will be a
HV to chassis short.. or a anode to grid flashover, etc. With
reverse connected safety diodes [ I use a pair of paralled 6A
diodes pointed one way... and a 2nd PAIR, pointed the other
way] .. connected between CHASSIS and B-.... the fault current
simply flows from chassis through the diodes... and back to B-
... completing the loop... and presto... the sand filled fuse in
the B+ blows.. every time ! Also use reverse connected
6A diodes across BOTH the grid and plate current meter's. You
will NEVER arc across the 250 V rated fast blow 3agc CATHODE
fuse !!





##### Question is... what's an easy way to obtain a visual

indication /led/neon/etc.... to let us know said fuses are
blown ???

TONY SEZ... If the cutoff bias is high enough, a neon bulb with a
series resistor could be used as an indicator.

RICH SEZ. It takes c. 90v to light neon. A LED takes c. 1v. Also,
with 1k=ohm and 3-500s, 25mA means the fuse is open, so one does
not need an idiot light.

####### When the big amp is 30' away... in a garage or a
workshop, etc...."idiot lights" def are needed !


RICH SEZ...Also, when the grid-I meter deflects backward, a tube
has a filament that is shorting to the grounded-grid.

### agreed. And the fix is to install reverse connected diodes
across the grid meter/shunt.... then the diode will conduct....
instead of deflecting ur grid meter backwards.


#### For some added protection... we are thinking of an
adjustable spark gap between load cap ...and chassis..... set
to fire at a V higher than the normal low swr V.... and a point
well below the rating of the 5 kv vac load cap. I think
Rich may have done this ?

RICH SEZ ..Correct


### I don't want the expensive ceramic vac load cap to ever
internally arc.

RICH SEZ.... Spark gaps are good! However, adding a rugged low-ohm
low-L resistor in series with the spark gap helps to limit peak-I
during a glitch.

### Huh ? This is HIGH RF voltage across the spark gap [across
the vac load cap]. What do u suggest.... a 50-500 ohm 90/150
watt globar ??? There's already a heavy duty glitch R in the
B+ of the HV supply. Adding R in series to any spark gap
may well slow down how fast the grid/cathode/ sandfilled HV
fuses blow ???

Later......Jim VERF

--- In ham_amplifiers@..., "Mike Sawyer" <w3slk@...>
wrote:

Hey folks,
I just planted the seed over there when the 'moderators'

weren't looking. A little wind may restart the kindling again.

Will is a good choice, he's a little more subtle than me;>)
Mod-U-Lator,
Mike(y)
W3SLK

######## Nice try Mike.......... it sure as heck didn't make it.
Now, W8JI et all... has pissed off HSU.... somebody should
tell HSU to move over here. HSU seems like a nice fellow....
now he's having to defend his country. The very latest post
is.... "the administrator" has reprimanded all of em ..again !

Later Jim VE7RF

ORIGINAL MESSAGE:

On Sat, 30 Sep 2006 05:21:57 -0700, R L Measures <r@...> wrote:

even on
issues that, to a RF-savvy person, make him look the clown.

------------ REPLY FOLLOWS ------------

Word is he's still out there with his grid dip meter looking for
series resonances. :-)

Bill, W6WRT

On Sep 30, 2006, at 10:53 AM, Tony King - W4ZT wrote:

R L Measures wrote:
<snip>

### Not quite. The GRID RING is bonded to the chassis !! This
is not a case like Rich using 1/2 watt resistor's as "grid fuses" [
which WILL leave the grid floating]

Tony -- Have you ever blown a grid fusing R and observed what happens?

nope,

Nothing happens. ...

R L Measures, AG6K, 805.386.3734
r@...

开云体育

R L Measures wrote:
<snip>

### Not quite. The GRID RING is bonded to the chassis !! This
is not a case like Rich using 1/2 watt resistor's as "grid fuses" [
which WILL leave the grid floating]

Tony -- Have you ever blown a grid fusing R and observed what happens?

nope, no grid fuse if the grid is bonded to the chassis directly ;)
I was referring to B- floating off ground but if it isn't, then there isn't an issue.

73, Tony W4ZT

R L Measures wrote:

I suppose you require the same deal on
just balancing TWO tubes ???? [2 x fil chokes + 2 x
blocker's]............ even the 2 x tube senario sucks.

With multi-tube indirectly-heated cathodes, adding cathode RF-NFB is a piece of cake, but with directly-heated cathodes it's a bucket of snakes.

Amen!! So true so true.

I remember building a 2 x 4-1000 amp... with two of

Smart move. If one needs more suds, go for One tetrode with handles.

Thats why I built a 8171! At one point Rich also gave me some help,
now it runs like a charm!

73 Jim SM2EKM

On the "other" reflector a statement was made about TPTG oscillators
and I posted a follow up question about the time of the Great
Migration to this reflector so I never did get an answer. I'd like to
ask it again here.

The 'Gentleman From Georgia' (you know who) made the comment that a
TPTG oscillator will not oscillate if the grid tank is tuned higher in
frequency than the plate tank. Under that condition, apparently the
phase of the fed-back voltage is wrong and oscillation can not occur.

Since this is essentially what a VHF parasitic oscillator is, it
caught my attention.

Is this statement true? If so, then it would seem that all one has to
do to achieve VHF stability is to make the two resonances meet the
above requirements. Can it be that simple?

TPTG oscillators - the intentional kind - have not been used in ham
circles for decades so I wouldn't be surprised if knowledge of them
has been pretty much lost.

All comments welcome.

73, Bill W6WRT

On Sep 29, 2006, at 4:16 PM, pentalab wrote:

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


RICH SEZ.. The V-drops across the cathode resistors is what helps to
equalize the cathode currents in the 4, 811As. However, 4,
individual bifilar filament chokes and 4. DC blocker/coupling caps
are needed.

### Well... that sucks !!

That's the awful reality of adding cathode RF-NFB with thoriated tungsten tubes in parallel

I suppose you require the same deal on
just balancing TWO tubes ???? [2 x fil chokes + 2 x
blocker's]............ even the 2 x tube senario sucks.

With multi-tube indirectly-heated cathodes, adding cathode RF-NFB is a piece of cake, but with directly-heated cathodes it's a bucket of snakes.

I remember building a 2 x 4-1000 amp... with two of
everything in it.... fil xfmrs... fil chokes... 2 x fil variacs...
separate adjustable bias....... and 3 x plate + 3 x grid current
shunts..... Tube 1.... Tube 2.... Tube 1+2. Then cross ur
fingers... and hope the drive split's into two equal parts...
ditto with airflow.

After that... I said I'd never build / design another 2+ tube
linear again..... I didn't.

Smart move. If one needs more suds, go for One tetrode with handles.

Just trying to trbl shoot a 4 x tube
amp is not fun. Still, I did have a 4x 811A linear.... and
the tubes never gave me any problems........ the rest of that
Dentron amp was pure junk.

Amen, Jim. Dennis Had is reportedly now in the AF amp business -- which is where he pretty obviously should have gone in the first place.

later.... Jim VE7RF








Yahoo! Groups Links

R. L. Measures, AG6K, r@somis,org, 805-386-3734

On Sep 29, 2006, at 4:53 PM, pentalab wrote:

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

RICH SEZ...Now the bad news: Without W8JI, the "recognized
amplifier expert", Charles Thomas Rauch, Jr., and his statements
such as the laws of AC circuit analysis do not apply to VHF
suppressors; and VHF resonant circuits can't ring, but HF ones can,
things will definitely be less entertaining.

### this is one soap opera I don't wanna ever hear again!

Why read it more than once? Before I started the grate parasite debate with Tom I was warned by a Ham in Manhattan that he wins debates in the eyes of his groupies by never backing down, even on issues that, to a RF-savvy person, make him look the clown. In my opinion, this is probably something he picked up from his father, Charles Thomas Rauch, Sr.
- editorial - If I go to my grave with a bunch of newbies believing Tom's statement that Ni-Cr alloys have reverse RF skin-effect, VHF resonances can't ring, et cetera, I will not be resting in peace - and that's for damn sure. .

### The best way to solve parasitic problems in a TL-922 SB-
220/221 is to REMOVE all 6 x 200 pf bylass caps + 2 x RF
chokes from sockets... and toss em !! Strap all 6 x grid
pins to chassis ..with wide strap..... end of problem.

The grid resonance in a stock TL-922 is in the high 80MHz range. The grid resonance with the grid pins strapped to ground is typically about 1MHz lower. How does this make the amplifier more stable at the 120MHz resonance in the anode circuit?

Rich, AG6K

On Sep 29, 2006, at 6:05 PM, pentalab wrote:

--- In ham_amplifiers@..., Tony King - W4ZT <w4zt-
060920@...> wrote:

pentalab wrote:

Fellows

I have several fuses installed in most of these linear's.

Like a fast 750 ma 3agc style grid fuse... located between
chassis.. and negative terminal of 0-1 Amp grid meter.

TONY SEZ... I'd protect this with diodes and leave that fuse out.

It wouldn't be a good idea for the cathode to ground circuit to
open and essentially float the grid.

### Not quite. The GRID RING is bonded to the chassis !! This
is not a case like Rich using 1/2 watt resistor's as "grid fuses" [
which WILL leave the grid floating]

Tony -- Have you ever blown a grid fusing R and observed what happens?

On Sep 30, 2006, at 12:16 AM, pentalab wrote:

--- In ham_amplifiers@..., "badgerscreek" <qrp73@...>
wrote:

So how do you come up with the inductance and resistance value for

the suppressor? Maybe you can give us some insights how you go about

designing a suppressor, certainly one size would not fit all? Can

you place a picture of your 3cx6000 suppressor on here?

### I think u can just see it in the pix. I posted a ton of pix
on "photo's".... just click on my VE7RF photo album..... it's got
the Coaxial dynamics 25 kw slug [for a 7/8" line section no
less.] on the front of the photo album.

### I do em by trial and error. On the 3000A7, I used the one
turn chrome plated suppressor from the 8K ultra. [it has NO
resistor]. Last year, Henry radio tells me .."the chrome did
nothing.. so we went back to silver plate strap". Now they are
telling me.. the LAST bunch of 8-K ultra's that left the factory
[b4 they lost their lease].. had NO suppressor's !! Turns out
the "parasitic problem" was a plate choke problem all along !!

The 3cx3000A7 has 0.6 pF of feedback C. That's 6x more than the 8877 and 4x more than a 3-500Z. At its max-f rating of 110MHz, the
3cx3000A7 has an output to input feedback path with 2500-ohms of XC.

I figured as much... since their 2 x piece plate choke uses 20 uh
+ 180 uh. [the 8-k uses a 3000A7] In MOST cases... on a HB
3000A7... u can just toss the suppressor.

... especially if you just love to repair amplifiers.

### On the 6000A7.... I was clueless. The 11-m boyz are using
250 W globars !!! I looked at JA6TAY's stuff... and he uses
flat strap... wound directly onto globars. You can only get 3
turns of 3/4" wide strap on a 5" long globar anyway.... so I
found that [50 ohms]... worked.. rock stable. Next trick... we
will remove it alltogether.. and replace with 1" wide flat strap..
and see what happens.

### I'm convinced... 98% of stability is how well the control grid
is grounded. A 3-500Z has only ONE internal grid pin....

It's a 360? cone shaped collet.

which
then splits into 3 x external pins... which bought em nothing.

If the 3-pins are grounded directly, the resonance at the grid is in
the 80MHz range. If the 3 grid pins are grounded through 200pF caps,
the grid resonance is in the 80MHz range. In my experiences it is better to measure resonance with a dipmeter than to guess at it.

These big triodes have huge 4.25" diam [almost 13"
circumference] grid rings on a 3000/6000. The grid ring on a YC-
156 is even bigger.... 5.25" diam [almost 16" circumference] !

### W8JI once modified a small GG metal triode... improved the grid
grnding... and built the worlds only [as far as I know] 160-6m
linear.... with NO parasitic suppressor !!

So why does the AL-1500 - that he apparently designed - have a
reputation for sudden 8877 failures? As I see it, an amplifier that
appears to be stable during an hour or so of testing is not
guaranteed to be stable in the long run.

### In any event...in yrs gone by.. I always start with a 50 ohm
globar.... and keep adding turns[ 1 1/2... 2...2 1/2....3] till the
parasitic goes bye bye. If using a real small globar... and u run
outa room.... reduce the width of the strap.

Smooth move. Reducing the width of the strap increases RF-
resistance, which lowers the L/R suppressor's VHF-Q, which in turn
lowers VHF gain and reduces the chance of VHF oscillation. Another
way of increasing RF-resistance is to choose a conductor that is more
resistive than copper. Example -- The 8169 / 4cx3000A amplifier at:

appears to have no parasitic suppressor whatsoever, however the anode
to blocking-cap connector strap, as well as the connection to the
Bruene-bridge neutralizing cap is made out of a nickle-chromium
alloy. According to (W6HW) - a friend who worked for Collins Radio
Co. - the 30S-1 amplifier used the same technique.
- Murphy was right: Things may be more complicated than they look.

What other mods have you made to the L4B? You still running the

stock power supply?

#### Sorta... same plate xfmr. I added external step start
which steps starts the HV + the fil xfmr. [25 ohm-100 w in ONE
leg]. I also disconnected the 2 x 50k- 100 w bleeders [ + the 7 k-5
watt resistor in series with em...used for the +130 V RX cut off
bias]. 99% of the heat from the top of the L4B/L7 HV supply
is from the 70 w CCS from those bleeders !

But it's a great coffee or soup-warmer.

Rich, AG6K

On Sep 30, 2006, at 12:22 AM, pentalab wrote:

--- In ham_amplifiers@..., "craxd" <craxd1@...> wrote:

All,

Hsu posted this at the other group. To be made in China, it looks a
lot like an AL-811 if you ask me. BTW, did anyone ever ask Hsu to

the

group here?



Best,

Will

### Will.... I'm gonna nonminate you as... "project
manager". ...so you can round up all these .."stragglers".... and
bring em over ...to the dark side.

Try posting this on AMPS to see if Tom is staying awake (he censors it).

Jim VE7RF







Yahoo! Groups Links

On Sep 29, 2006, at 4:56 PM, Tony King - W4ZT wrote:

pentalab wrote:

Fellows

I have several fuses installed in most of these linear's.

Like a fast 750 ma 3agc style grid fuse... located between
chassis.. and negative terminal of 0-1 Amp grid meter.

I'd protect this with diodes and leave that fuse out. It wouldn't be a
good idea for the cathode to ground circuit to open and essentially
float the grid.

When a high-R exists in the cathode circuit, as soon as a little current begins to flow, the tube cuts off. My modified SB-220 and TL-922 do this, and if a tube ever happens to short, nothing is damaged.
- note - In a stock SB-220 or 922, a shorted tube can destroy the filament transformer in short order.

Also have a 3 A cathode fuse [also a 3agc] in the center tap of
the fil xfmr circuit [ along with the 60 x 6A10 6-A , rotary
switched bias diodes. ] This 3 A cathode fuse has a 1k-25
watt ressitor across it.

1k is a little low, use something like 15K to 20K across the fuse. When
the fuse blows you will have an increase in bias that will cut the tube
off and will develop a voltage proportional to that needed to cut it off.

With 3-500Zs, 1k-ohm will limit anode current to about 25mA when the fuse opens.
- editorial - A 250v-rated fuse in a circuit operated by 3000v is not good engineering practice.

Question is... what's an easy way to obtain a visual
indication /led/neon/etc.... to let us know said fuses are
blown ???

If the cutoff bias is high enough, a neon bulb with a series resistor
could be used as an indicator.

It takes c. 90v to light neon. A LED takes c. 1v. Also, with 1k=ohm and 3-500s, 25mA means the fuse is open, so one does not need an idiot light. Also, when the grid-I meter deflects backward, a tube has a filament that is shorting to the grounded-grid.

... ... ...

For some added protection... we are thinking of an adjustable
spark gap between load cap ...and chassis..... set to fire at a
V higher than the normal low swr V.... and a point well below the
rating of the 5 kv vac load cap. I think Rich may have done
this ?

Correct

I don't want the expensive ceramic vac load cap to ever
internally arc.

Spark gaps are good!

However, adding a rugged low-ohm low-L resistor in series with the spark gap helps to limit peak-I during a glitch.

Sri for the drivel....... does anybody actually read any of my
posts....... or is this all old news ???

Later... Jim VE7RF

I enjoy reading your posts Jim!

Best thing I have seen is to use one of the triode control boards and
use the protection circuitry they provide. You will find there's hardly
any failure that will can not be detected and reacted to almost
instantly. You might have to make a few adaptations to meet the need for
QRO++ but the principle is the same. This is especially good because it
can trip the amp off line so you don't have high drive going into a
malfunctioning amp.

73, Tony W4ZT



Yahoo! Groups Links

--- In ham_amplifiers@..., "craxd" <craxd1@...> wrote:

All,

Hsu posted this at the other group. To be made in China, it looks a
lot like an AL-811 if you ask me. BTW, did anyone ever ask Hsu to

the

group here?



Best,

Will

### Will.... I'm gonna nonminate you as... "project
manager". ...so you can round up all these .."stragglers".... and
bring em over ...to the dark side.

Jim VE7RF