On Oct 2, 2006, at 12:41 PM, pentalab wrote:

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

On Oct 2, 2006, at 12:15 AM, pentalab wrote:

### partially agreed. IF u have a HV fuse... and it opens...

the grid current will skyrocket..... hence another reason for a
fast grid fuse.

#### STEVEN SEZ... * OK, question - will the fuse blow if the
tube becomes unstable

(parasitic oscillation)

#### Been a long time since I have experienced parasites....

seems to me, both the plate current and grid current went
beserko.

RICH SEZ indeed

#### IF the HV fuse opened off... the grid fuse would blow

instantly...

RICH SEZ ..quite soon is more like it

### No, not quite soon,,, grid fuse blows asap ! instantly !

Instantly is pretty soon.

You remove the HV on any GG amp... AND drive it, with just a
little bit of power.. you will send the grid current through the
roof ! You drive it with full power.... and then lose the HV...
the grid current will wrap around the peg 4 x over..... and
blow the fast grid fuse.

### Fast fuses are called ..."rectifier fuses". The even
faster ones of the bunch are called .."semi conductor fuses".
You can even get fast .. "semi conductor fuses" up to 300 A

## You can get super fast fuses in 3agc.. anywhere.. like
Mouser/digi key/newark, etc.

### Never had a problem with parasitics destroying a tube.. as
long as glitch R installed... grid and cathode fuses... and a
HV fuse.

RICH SEZ... As I see it, a HV fuse is OBVIATED if the HV xfmr
primary is fused.



### DREAM ON RICH Rich ! You gotta be nuts to leave out the
HV fuse.... and soley rely on a typ slow breaker in the 240 V
primary !!! The fastest breakers known.. are
called "controlled Hydraulic magnetic breakers".... and the
fastest of them .... still isn't fast enough.

HV fuses are not fast enough to prevent gold sputtering from the grid of an 8877, 3cx800A7, et cetera.

## Here's why. The last HV supply I designed used 30 x
lytics... EACH is 3700 uf @ 350 V. We ran outa 3700 uf
units for the last 5 caps.. so we used 5200 Uf units @ 350 V.

### The entire mess > 135 uf !! Since joules [watt seconds]
goes to the SQUARE of the voltage..... u can easily see that the
total joules is sky high..... has to be. You want to run 10 x
the dc input as b4.... u require 10 x the energy in joules.

### Even on a SB-220, L4B, AL-1500, etc.... the stored energy
in the bank of lytics is just unreal.

The SB-220's 120J seems pretty real to me.

A Buss HVU series, sand
filled fuse [sized right for the job] OR a HB hv fuse [ one fine
strand between 2 x insulator's] will blow EXTREMELY
FAST......<2- msecs.

Peak current can go through the roof in under 1mSec.

### The ONLY way to speed up the primary 240 V fusing.. is to
supplement the typ "controlled magnetic hydraulic breakers"...
with super fast "semiconductor fuses" ....... or do like you
do.... and use a 40 A breaker..... which BARELY handles the
average load on unprocessed SSB. Of course, with a grossly
undersized breaker.... you only have two options..... pulse
tuning... and then straight to unprocessed SSB. Run a dead
cxr... even for 2 seconds, just to take some steady state
grid/plate/fil V readings.... and ur 40 A breaker will blow
open !! To do 14kw out.... you need a 100 A breaker !!

Been there. The original Plywood Box did 14-out PEP on SSB, it used a double 40A breaker and #4 Cu wire. I tuned it up with a 30pps, 30% duty-cycle tuning pulser, and it never tripped the breaker

### It's actually 106 A [and that's with 67% tank eff]

### Ur 100' of 4 ga wire has way too much loop resistance for
the peak currents on the 240 v line.

The HV dropped to c. 7800v on an ahhhhhh. What's wrong with that?

A bare minimum for just
a 30' run is 2 ga. It should be 3 x 000 CU.... regardless
of lenght.

### leaving out the simple HV fuse.. and relying on primary
breakers is a 100% sure fire way to destroy stuff.. including
tubes.

Perhaps an indirectly cathode could be damaged by over-current, but directly-heated cathodes are naturally current limiting. The 8170 in the Plywood Box amp was not damaged during a number of big-bang parasitic oscillations, but I disintegrated a few glitch resistors before I figured out that a glitch-R is Not supposed to be a fuse. .

...

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

What is your reason for that large capacitor?
Are you using single phase at that power level?
I only use 2?F maximum or none in my large power supplies, so my glitch
resistors and magnetic breakers in the primaries of the transformers is all
I need

73
Peter, DF3KV

________________________________

From: ham_amplifiers@... [mailto:ham_amplifiers@...]
On Behalf Of pentalab

## Here's why. The last HV supply I designed used 30 x
lytics... EACH is 3700 uf @ 350 V. We ran outa 3700 uf
units for the last 5 caps.. so we used 5200 Uf units @ 350 V.

### The entire mess > 135 uf !! Since joules [watt seconds]
goes to the SQUARE of the voltage..... u can easily see that the
total joules is sky high..... has to be. You want to run 10 x
the dc input as b4.... u require 10 x the energy in joules.

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

RICH SEZ...Correct. Jim. My thinking on NOT using a fuse holder is
that if the fusing element blows, the reason is not a defective
fuse, it has to be the whatever that caused the fuse to blow, so a
new fuse is not the total repair. Thus, when the fusing element
blows, the amplifier has to be disassembled anyway to find the
real problem, so a fuse holder would be of no advantage.

### Gimme a break ! The grid fuse could blow for several
reasons.... like SKY high swr... accidental overdrive....
underloading, both..... OR if the HV fuse blew open [and with amp
being driven, the grid current will wrap around the peg].

## once the reason for the grid fuse blowing is known.... it can
be quickly replaced... in mere seconds flat. Ditto with a
cathode fuse. A little longer to replace either of the HV fuses.

### I can stuff a screwdriver into the HV compartment, grnd
anything you want, short out caps, short the grid to the
cathode... run 15 kw into a dead short, wide open,,, drop a wrench
across the 240 v input, have the big Dayton blower crap out, lose
air to the tube , lose commerccial AC power from the street,
have transients, spikes , surges coming in off the street,
overdrive the amp, underload the amp, etc, etc... and you STILL
CAN'T blow anything up. I can even lay a dead short across the
diode FWB rectifier board.... and not take out any diodes.

### I can also short out the fil xfmr, or short out the + 120
vdc supply for the sped up vac relays, or short out the +12
vdc for the plate choke relay.

### My goal was to make it [RF deck + HV supply] 120% BULLET
PROOF!! Next step is to add the spark gap across the Vac load cap.
[heck a spark plug in open air.. set to arc at 1.7 kv will work]
We might add electronic grid + plate overcurrent protection
later on... + a HV sensor [which will inhibit TX... with low, or
NO hv present].

### The beauty of HB designs is.... you can easily add any or
all of this stuff in... at any time.... and it's all dirt cheap....
just like copper tubing.

Later... Jim VE7RF

I check in here every few days to count on my mental fingers how many
times Rich rants on about Tom...
Then I go to the other shrine and count how many times Tom mentions
Rich...
It's umpteen to zero at this point...
One of em needs to give it a rest!

- busily changing out 20K ohm, 100 watt, resistors in a Henry 3K
Ultra PS.... Man a bad PS load resistor can sure contaminate
everything when it decides to go open winding and arcs, sputtering
crap onto other components...
It took a bit of sleuthing to find the correct resistors for
replacing... Turns out Newark has em in Ohmite brand...


denny / k8do

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

On Oct 2, 2006, at 12:15 AM, pentalab wrote:

### partially agreed. IF u have a HV fuse... and it opens...

the grid current will skyrocket..... hence another reason for a
fast grid fuse.

#### STEVEN SEZ... * OK, question - will the fuse blow if the
tube becomes unstable

(parasitic oscillation)

#### Been a long time since I have experienced parasites....

seems to me, both the plate current and grid current went
beserko.

RICH SEZ indeed

#### IF the HV fuse opened off... the grid fuse would blow

instantly...

RICH SEZ ..quite soon is more like it

### No, not quite soon,,, grid fuse blows asap ! instantly !
You remove the HV on any GG amp... AND drive it, with just a
little bit of power.. you will send the grid current through the
roof ! You drive it with full power.... and then lose the HV...
the grid current will wrap around the peg 4 x over..... and
blow the fast grid fuse.

### Fast fuses are called ..."rectifier fuses". The even
faster ones of the bunch are called .."semi conductor fuses".
You can even get fast .. "semi conductor fuses" up to 300 A

## You can get super fast fuses in 3agc.. anywhere.. like
Mouser/digi key/newark, etc.




### Never had a problem with parasitics destroying a tube.. as
long as glitch R installed... grid and cathode fuses... and a
HV fuse.


RICH SEZ... As I see it, a HV fuse is OBVIATED if the HV xfmr
primary is fused.



### DREAM ON RICH Rich ! You gotta be nuts to leave out the
HV fuse.... and soley rely on a typ slow breaker in the 240 V
primary !!! The fastest breakers known.. are
called "controlled Hydraulic magnetic breakers".... and the
fastest of them .... still isn't fast enough.

## Here's why. The last HV supply I designed used 30 x
lytics... EACH is 3700 uf @ 350 V. We ran outa 3700 uf
units for the last 5 caps.. so we used 5200 Uf units @ 350 V.

### The entire mess > 135 uf !! Since joules [watt seconds]
goes to the SQUARE of the voltage..... u can easily see that the
total joules is sky high..... has to be. You want to run 10 x
the dc input as b4.... u require 10 x the energy in joules.

### Even on a SB-220, L4B, AL-1500, etc.... the stored energy
in the bank of lytics is just unreal. A Buss HVU series, sand
filled fuse [sized right for the job] OR a HB hv fuse [ one fine
strand between 2 x insulator's] will blow EXTREMELY
FAST......<2- msecs.

### The ONLY way to speed up the primary 240 V fusing.. is to
supplement the typ "controlled magnetic hydraulic breakers"...
with super fast "semiconductor fuses" ....... or do like you
do.... and use a 40 A breaker..... which BARELY handles the
average load on unprocessed SSB. Of course, with a grossly
undersized breaker.... you only have two options..... pulse
tuning... and then straight to unprocessed SSB. Run a dead
cxr... even for 2 seconds, just to take some steady state
grid/plate/fil V readings.... and ur 40 A breaker will blow
open !! To do 14kw out.... you need a 100 A breaker !!

### It's actually 106 A [and that's with 67% tank eff]

### Ur 100' of 4 ga wire has way too much loop resistance for
the peak currents on the 240 v line. A bare minimum for just
a 30' run is 2 ga. It should be 3 x 000 CU.... regardless
of lenght.

### leaving out the simple HV fuse.. and relying on primary
breakers is a 100% sure fire way to destroy stuff.. including
tubes.

RICH SEZ Also, a fuse is not as good as of a peak-current limiter
as a glitch R.

### A fuse is NOT a peak limiter at all... never was ! A fuse's
job is to INTERUPT CURRENT FLOW... that's it. The job of the
glitch R is to LIMIT CURRENT. You need BOTH... and the
glitch R should be 50 ohms.... even in a small amp.

### To really do it right... I install a 2nd HV fuse.... located
between ONE leg of the plate xfmr sec... and the diode board...
with this arrangement... there is NO way you can ever take out
the diodes.

### also install one reverse connected 6 A diode ACROSS EACH
lytic.

### In a small amp, use a 50 ohm 50 watt wirewound... OR 2 x 25
ohm-25 Watt units in series....[the 2 resistors can be several
inches apart.. easier to mount in some apllications.]

Later... Jim VE7RF

On Oct 2, 2006, at 12:15 AM, pentalab wrote:

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

STEVEN SEZ... * In normal amateur service, i dont see how i could

ever drive the amp hard enough to roast the grid

even if mistuned (2 3-500Zs)
I dont tune with full power till im close to resonance btw
(maybe a 3CX800)

### partially agreed. IF u have a HV fuse... and it opens... the
grid current will skyrocket..... hence another reason for a fast
grid fuse.

#### STEVEN SEZ... * OK, question - will the fuse blow if the
tube becomes unstable

(parasitic oscillation)

#### Been a long time since I have experienced parasites.... seems
to me, both the plate current and grid current went beserko.

indeed

IF
the HV fuse opened off... the grid fuse would blow instantly...

quite soon is more like it

### Never had a problem with parasitics destroying a tube.. as
long as glitch R installed... grid and cathode fuses... and a HV
fuse.

As I see it, a HV fuse is obviated if the HV xfmr primary is fused. Also, a fuse is not as good as of a peak-current limiter as a glitch R.

later... Jim VE7RF








Yahoo! Groups Links

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

On Oct 1, 2006, at 4:05 PM, Bob Green wrote:

Hi all –

I have what used to be a working SB-200 amp. It is not working well
at all now. I really want to get it on the air for the CA QSO Party
next weekend. I come to you as a last resort.

I used to be able to get about 700 watts out on 20M. Now I’m lucky
if I can get 50-80 out, with 40-70 IN. The 572 plates get bright
red-orange, but no (or nearly no) power out. Someone on the OTHER
reflector suggested the 33 ohm grid resistors were open. They are
not. One was about 33.9 ohms and the other was about 45 ohms, but
definitely NOT open.

45 ohms is 36% high. If the outside of the resistor is not burned,
the resistor may have been damaged by an intermittent condition,

In looking at AG6K’s website, it shows the 33 ohm resistors in
parallel with approx 900 pf directly to ground, not through the
Heath bias circuitry. I have no problem connecting the amp like
this, but will it really help?

It does not help stabilize the amp, it's a mod that obviates the
cockamamie Heath T/R biasing scheme and allows one to do the needed
high-speed switching mod.

And how do you read grid current, since none would be flowing
through the meter?

Grid current flows from the grid through the 33Ω resistor to gnd,
from gnd through the grid current meter shunt, to the negative HV,
the same way the SB-220 meters grid current. .
... ...
cheers, Bob

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

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

On Oct 1, 2006, at 4:43 AM, pentalab wrote:

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.

RICH SEZ...Agreed. Henry parasitic suppressors typically have a

Q of >5 at > 100MHz. IMO, it's better to keep suppressor Q under 2.

### The 8 k is rock stable... with a 1 turn strap of 1" wide
chrome plated material... which is doing nothing..... toss it... and
it's still rock stable.

RICH SEZ... How long is the 1" strap used to ground 3=500Z socket
pins?

### about 1.5".... which measures ZERO inductance on my B+K 875B
LCR meter. ... which only reads down to .1 uh. Heck.. a 3' long
piece of 3/4" wide CU strap still reads 0.0 uh.


### 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...

RICH SEZ... Not in my experiences. Increasing the grid's resonant

frequency should theoretically allow the grid to better shield the
output from the input at higher frequencies -- thereby increasing
VHF stability.

### DEEP SIX the "theoretically part". When doz's of
fellows tell me that after grnding the grids to chassis with
strap on the TL-922 and SB-220/221's makes em rock stable,
believe it. And they also re-installed the STOCK OEM
suppressor's to boot.



###... as to why it works is perhaps the grids are now really
grounded...

RICH SEZ Up to what frequency?

### Dunno... probaly good to 6m... since 3-500Z's seem to
work just fine on 6m... in GG... with the grids dirctly grnded.

### Now the AL-80BX and Ameritron with the 2 x 3-500Z's do

have the grids directly grnded.... and STILL spit, arc, etc.

Perhaps it involves something other than the grids -- such as the

Q

of the R/L VHF suppressor @ 100MHz? Please describe the VHF
suppressors.

### TYP Ameritron junk.

L4Bs are inherently more stable than most other 3-500Z amps

because they use less HV to supply the anodes -- and that
decreases gain.

### agreed. They also use real suppressor's.

### I once built asingle 3-400Z in 1974... had 5000 vdc no
load on it. Rock stable.... with grids directly grnded... and a
suppressor made with 12 ga wire and a globar.

### Lemme ask u this. IF u were gonna design and build a 2 x 3-
500Z 80-10m amp from scratch.... would directly grnd the grids
with strap..... OR install 6 x 200 pf caps + 2 x RF
chokes ??????


RICH SEZ... a glitch resistor is needed to physically limit peak
filter-cap current to under 200A during a glitch . Neither a HV
fuse nor a typical over-current trip circuit is fast enough or
rugged enough to do this job.

### a HV fuse does NOT limit current. It INTERUPTS it.

### a FAST HV fuse..a cathode fuse....

RICH SEZ.......250 V rated ?

### 250 V rated cathode 3agc fuse work just fine. As
explained b4... they will NEVER see 3000 vdc in a million yrs.....
not with reverse connected diodes between chassis and B- ...
and more reverse connected diodes across both grid + plate
meter's.


### and a real 50 ohm, 50-100 w glitch resistor.

RICH SEZ... Agreed, but limiting peak current that severely with a
3kV PS may not be needed.

### Do u want to limit the current or not ?? A 50 ohm 50 W wire
wound is good up to 1 A of plate current in normal operation...
limits current to 60 A...... then the HV fuse blows instantly...
followed by the grid fuse. [since grid I will skyrocket, with
drive applied, and NO HV]



### Use of a digital delay for cw + ssb will help
immensely.....

RICH SEZ no delay is needed if the relays are faster than the
transceiver.

### I'm using fast RJ1-A's on the input [+120 vdc speed up]
and slower paralled sped up vac relay's on the output [8 msec]. I
don't want the drive being applied... and still no ant
connected... yet.

### these modern xcvr's crank out globs of RF instantly...

RICH SEZ 5mS is typical

### measure it on SSB. Moot point. The MK-V's have an
adjustable 0-30 msec digital delay on cw [no truncated
anything]. On ssb we use the 10 msec delay scheme.. and play
it safe.

RICH SEZ An RJ-1 or HC-1 makes in c. 1.8mSec with the circuit at:

However such speed requires 100 to 150 volts at the other end

of the current limiting R.

### Even paralled RJ-1A's are flaky on the output of a big amp.
I used a paralled pair of Jenning/Kilovac/ Gigavac next size up
units... rated at 10 A @ 32 mhz.... and tons of voltage. Handles
an easy 20 kw dead cxr on 10m.... and more on the lower bands.

## They are not fast though. Stock, they are 18 msec operate..
and 9 msec release. I speed em up with +120 vdc... chops the op
time way down.... to 6-7 msecs. No qsk.. fast vox cw/ssb.

### Also, xcvr's like the ICOM's.. will have peak overshoots.
That's easy to fix...... just use fixed dc voltage.. fed to the
ALC jack at all times !

RICH SEZ Turning the mic. gain down to barely any ALC greatly
reduces overshoot and usually slightly increases PEP. .

### Waste of time. I use loads of external audio rack gear. My
Aphex 320A levelor /compressor/limiter feeds a constant level of
audio into my Aphex 720A "Dominator" [split band
limiter/distortion cancelled clipper]. I can get an easy 200 w
pep.. or any pwr level I want... and not have the ALC meter even
budge.. scream all I want.


#### 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 !!!

RICH SEZ Agreed. For an 8171 on 10m, expect 25A-rms.

## It's a helluva lot more than that.


### Here's my problem with Nichrome. It GLOWS ORANGE on the

higher bands.

RICH SEZ Use a width that will carry the current. I use 4-mil
stainless-steel shimstock, cut to the width I need for big ones.

### Why not just use the correct component in the 1st place ??
A 90 w globar 3/4" diam x 5" long....... bullet proof... and
nothing gets hot.... rock stable.



RICH SEZ But you would achieve a lower VHF Q if you used stainless-
steel shimstock or Ni-Cr ribbon.


### agreed, but the above globar + a few turns of WIDE Silver
plated strap do the job. Just increase the turns till parasites
go bye bye.

### U can do the exact same thing on a SB-220 if u want. Just
increase the turns in the suppressor till parasites gone.
Resistor getting hot on 10m/burning up ?? Gee... replace with
the correct component... a small 10-25 w globar.

#### IMO use what ever works. I had a ton of globars on hand...
and loads of strap. They carry 3' x 7' sheets of CU... in any
thickness... and I just get em to chop it in 3' lengths... usually
in 3/4" widths.. and also 1" widths. The globar method
involves soldering..nothing.

## all connections to tank coils and bandswitch contacts use
machine screws.

### BTW, the new Gigavac heavy duty relays all have machined
and tapped threads on the connections... for a 6-32 screw....
so takes strap easily. On the jenning's and kilovac units...
they stuff 8 ga wire inside the same tubes.. and solder em.

Later... Jim VE7RF

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

STEVEN SEZ... * In normal amateur service, i dont see how i could

ever drive the amp hard enough to roast the grid

even if mistuned (2 3-500Zs)
I dont tune with full power till im close to resonance btw
(maybe a 3CX800)

### partially agreed. IF u have a HV fuse... and it opens... the
grid current will skyrocket..... hence another reason for a fast
grid fuse.

#### STEVEN SEZ... * OK, question - will the fuse blow if the
tube becomes unstable

(parasitic oscillation)

#### Been a long time since I have experienced parasites.... seems
to me, both the plate current and grid current went beserko. IF
the HV fuse opened off... the grid fuse would blow instantly...

### Never had a problem with parasitics destroying a tube.. as
long as glitch R installed... grid and cathode fuses... and a HV
fuse.

later... Jim VE7RF

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

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

### IF the tube fil shorted to the grid... u may well be
correct. The CT of the fil xfmr would be tied to the
chassis... via the neg terminal of the grid meter [through the grid
fuse... then to chassis] This would short out the CT to BOTH
halves of the fil xfmr sec... frying it........ unless either a grid
fuse installed... or a fuse installed in the pri of the fil xfmr.

later... Jim VE7RF

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

I see that there's one of these on that e-auction place for ~$57.

I
understand that this is a pretty good tube since it doesn't require
any special socket. If I didn't have so many irons in the fire, I'd
snag this. But hell, I don't use my amp enough as it is. So here it
is
with about 2hrs. to spare.

Tube_W0QQitemZ110037289265QQihZ001QQcategoryZ58174QQrdZ1QQcmdZViewIte
m

Mod-U-Lator,
Mike(y)
W3SLK

### The F1 version only has a MU = 5......... so it's useless
for GG !

### It looks IDENTICAL to the 3CX-3000F7 MU= 200 which can be
used in GG. Both versions have flex leads to both the fil
connections AND the grid..... which makes it a pain to mount.

### Here's what fellows do to mount a 3000F7. Disconnect the
flex lead for the grid... and toss it. Replace with a vac var
flange for the same od of the grid ring on the tube.

### Bolt the new vac variable flange to the chassis... so the
tube is pinched/compressed by the new vac var flange. Connect the
fil flex leads to the bifilar [shorten em up 1st]... done.

### some will make /machine a split block of aluminium... both
halves of this block are simply bolted to the chassis... and
transverse machine screws compress the two halves together....and
pinch/compress the grid ring on the tube......again, the original
flex lead to the grid is tossed 1st... and fil leads are
connected as above... done.

### This info is just in case somebody comes across a F7 version
[identical tube to a 3CX-3000A7].

Both the vac flange and machined block idea came from some 11 m
op.... who had 3 x F7's in parallel... mounted exactly as
described... and that was in a mobile !!

later...Jim VE7RF

This wouldnt be the core problem I guess but if a
33 ohm resistor has changed to 45 ohms it needs to
be replaced, I hope you have done it already.

To me it sounds like the problem is on the output
side, since you can drive "input power" , check
from DC blocking cap and all the way to antenna
connector. Dont forget the RFC and the power
meter pickup.

73 Jim SM2EKM
----------------

Bob Green wrote:

开云体育

Check your plate blocking cap and pi - network components. Also TR RELAY contacts. Sounds like you have plenty or drive but output circuit may beon th ewrong frequency. Plate and load settings changes would be a clue. You could be tuning up on 10 meters. Blocking cap open would not couple rf to the tank.?wa1gfz

Bob Green wrote:

开云体育

Hi all –

I have what used to be a working SB-200 amp. It is not working well at all now. I really want to get it on the air for the CA QSO Party next weekend. I come to you as a last resort.

I used to be able to get about 700 watts out on 20M. Now I’m lucky if I can get 50-80 out, with 40-70 IN. The 572 plates get bright red-orange, but no (or nearly no) power out. Someone on the OTHER reflector suggested the 33 ohm grid resistors were open. They are not. One was about 33.9 ohms and the other was about 45 ohms, but definitely NOT open.

In looking at AG6K’s website, it shows the 33 ohm resistors in parallel with approx 900 pf directly to ground, not through the Heath bias circuitry. I have no problem connecting the amp like this, but will it really help? And how do you read grid current, since none would be flowing through the meter?

I’m kind of new at this, so if someone would be willing to call me instead of just jotting down some thoughts, I’d really appreciate it. Like I said earlier, I want to get this beast ready for a contest next weekend. I have two new tubes, but would rather not use them unless it is really necessary.

Thanks in advance for your help!? My phone is 909-866-7742. If you would rather, send me your phone number, and I’ll pay for the call. I have unlimited long-distance service.

73,

Bob Green W6BBL

w6bbl@...

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On Oct 1, 2006, at 2:40 AM, pentalab wrote:

--- 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.

Correct. Jim. My thinking on not using a fuse holder is that if the fusing element blows, the reason is not a defective fuse, it has to be the whatever that caused the fuse to blow, so a new fuse is not the total repair. Thus, when the fusing element blows, the amplifier has to be disassembled anyway to find the real problem, so a fuse holder would be of no advantage.

73 Jim VE7RF

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r@..., , rlm@..., www.somis.org

I just invited Hsu. I've been away for a couple of days and just got
to it.

What did Tom have to say to Hsu about the 811 amp? I don't get any
mail from Tom since I put him in my junk mail filter;)

What I did read from Hsu, is that he said the Chinese one was built
better internally, had been re-designed, and that the Ameritron was
junk compared to it, or was the jest of it. Didn't Tom supposed to
have a hand in the 811?

Best,

Will


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

On Sep 30, 2006, at 10:46 PM, pentalab wrote:

--- 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

!

Is the Administrator clueless or what?

Later Jim VE7RF









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

Bill Turner escribi:

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.

According to Bill Orr's 1959 handbook descritpion for TPTG oscillators:

"The feedback of energy from the plate to the grid circuits is accomplished by the plate-to-grid inter-electrode capacitance within the tube. The necessary phase reversal in feedback voltage is provided by tuning the grid tank capacitor to the low side of the desired frequency and the plate capacitor to the high side."

This means lower than resonance at the grid tank, higher than resonance at the plate tank; so based in those conditions, the above statement by the "you know who" guy is right.

From Terman's Radio Engineering Handbook 1943 Ed.:

"In the tuned-grid tuned-plate circuit, the grid tuned circuit LgCg and the plate tuned circuit LpCp, are both adjusted to offer an inductive reactance at the frequency to be generated. The circuit can accordingly be redrawn as shown in Fig. 1h [E.N.:not posted in this e-mail], and is seen to be the equivalent of a Hartley circuit in which the ratio of exciting voltage to alternating plate-cathode voltage is determined by the relative amounts of detuning of the plate and grid circuits.
The capacity Cgp [E.N.: shown in parallel with the coil that ressembles the lower portion of the Hartley oscillator coil] is usually supplied by the interelectrode capacity of the tube, although at lower frequencies added shunting capacity is helpful".

But, this gets me confused; if both circuits are adjusted to be inductive,
this means XL is lower, so both are adjusted at a frequency lower than
resonance. Not at either side as stated in Orr's text.
I'll look the equivalent Hartley circuit perhaps I'll see this better. Each tuned circuit adds its phase reversal to make the circuit oscillate.


Best regards
Guillermo - LU8EYW.

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 Oct 1, 2006, at 2:29 AM, pentalab wrote:

--- 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 ??

An 80Vrms winding is on the unfused fil xfmr. When rectified it produces c. 110Vdc. During RX, 110Vdc is applied to the fil CT to cut the tubes off. When a fil-grid short takes place, the 110v is shorted to gnd and, if the amp is not switched off, the filament xfmr will eventually melt down.

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......

Bingo


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