--- 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@...

All email scanned by the latest update of Norton Anti-Virus 2006 and is certified to be 100% virus-free.

开云体育

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

Yahoo! Groups Links

R L Measures, AG6K, 805.386.3734
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









Yahoo! Groups Links

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@...

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









Yahoo! Groups Links

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

On Sep 30, 2006, at 10:46 AM, Jan Erik Holm wrote:

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.

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

And in the Winter it keeps you warm.

73 Jim SM2EKM






Yahoo! Groups Links

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

On Sep 30, 2006, at 6:01 PM, Bill Turner wrote:

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. :-)

chortle. Tom abhors dipmeters because they give false dips -- or so he says when they do not confirm his dicta.

Bill, W6WRT



Yahoo! Groups Links

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

On Oct 1, 2006, at 3:09 AM, 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"

I read posts on parasites to check for specious statements.

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.

Agreed, but his groupies know that checking out the leader's dicta ist verboten.

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]

G2DAF amplifiers still use the 2-tone test because it produces about 1/11 the distortion products that a human voice produces in a G2DAFfy amp. .

### Rich, I think you are a.. " #5 " on the Energram
personality trait book [#5's love to argue].

I like to debunk taurine feces before some newbies swallow it.

Did you get burned
in the high school debating team ??

I have never been on a debating team. My bailywick is debating one on one when I am familiar with the subject. When I'm not, I know to shut up and listen to what other folks have to say. ... ...

### Why anyone would wanna leave in the 6 x 200 pf caps + 2 x
chokes is beyond me.

It increases the grid resonance freq slightly.

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.

Grid fusing is somewhat cheaper than tubes.

Jim VE7RF

Rich, AG6K

Yahoo! Groups Links

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

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

--- 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 ??

Jim -- A 2500-ohm feedback-path from the output back to the input of
a tube with an amplification factor of 200 means nothing to you?

IMO... the grid is better grnded on a
3000A7... than a 3-500Z.

It may be but both tubes have more than zero feedback C and more than
zero L in their grids.

### 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.

Agreed. Henry parasitic suppressors typically have a Q of >5 at
100MHz. IMO, it's better to keep suppressor Q under 2.

### 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

(4.8mm / 0.19")

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.

How long is the 1" strap used to ground 3=500Z socket pins? What is
the resonant frequency of a 3-500Z grid when it is so grounded? What
is the resonant frequency of the grid in a stock TL-922 or stock SB-220?

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 ???

those who want to employ good engineering practice.

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...

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. The fly in the pie is that most of the L that results in the grid's
88MHz or so resonance is inside the envelope.

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...

Up to what frequency?

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.

Perhaps it involves something other than the grids -- such as the Q
of the R/L VHF suppressor @ 100MHz? Please describe the VHF
suppressors.

[the
guys on the east coast em.. the "firecracker's " ].

chortle. With 0.3pF of feedback C, it ain't easy to get good stability.

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.

L4Bs are inherently more stable than most other 3-500Z amps because
they use less HV to supply the anodes -- and that decreases gain.

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

*** 250V rated?

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

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

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.

Agreed

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

No delay is needed if the relays are faster than the transceiver.

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

5mS is typical

even if the sped
up vac relay does operate in < 2msec.

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.

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 !

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

### 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 !!!

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

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.

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

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.

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

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.

Not if it's wide enough.

### 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.

I am aware of this. At 50MHz, 2" nichrome ribbon has c. the same RF
resistance as copper ribbon 0.35" wide. However, the DC resistance
ratio of Ni-Cr to Cu is c. 50 to 1.

Rich, when u
finish ur 4 x 10... fire it up.... on 10/12m...

The max frequency will be 22MHz. On 10m, when the band is open 100w
is plenty. When 10m isn't open, 10kW is not enough.

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

cheerz

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

At 08:17 AM 10/1/2006, pentalab wrote:

--- In ham_amplifiers@..., Steven Grant
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.

?* 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)

???? I do agree that with the grid open, the tube is off

????? I have seen roasted filament transformers from filament to grid shorts

### 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

? * OK, question - will the fuse blow if the tube becomes unstable (parasitic oscillation)
?????

### 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

thanks

? Steven W4IIV

--- 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: