Re: Gi46b on 2m - Thermal drift problem
+1 on the blocking cap. I have a 2xGI7B project on the go for 144MHz with a very similar set up, and the looming possibility of thermal drift is a great concern. I thought about employing one of those russian doorknob caps but chose a design that uses 2 slabs of copper with a PTFE sheet between them instead because I had read about thermal issues with those caps elsewhere. Time will tell if that was a good choice or not! Hopefully if the cap is your main issue, you can find a suitable replacement that doesn't send you back to cutting too much metal.
Further, maybe check the rating on your fan as well. You might want to get one with higher CFM. You'd probably do even better if you replace it with a small centrifugal blower that can pressurize the compartment. Muffin fans aren't so good at moving air against static pressure. The tube itself only needs 15 CFM, which isn't much... but if it's only a 15 CFM fan to begin with, it probably can't attain that through the restrictions in the compartment.
Also, I think the thicker the copper sheet, the more stable it will be (ie; more mass). If the copper is quite thin, you might never get it stable... though that might be more relevant to my chosen design than yours.
Good luck, hope to see an update on the outcome! :)
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Re: [Amps] [ham-amplifiers] Fw: [yccc] Followup: KM1H
We are always learning! ?
On Tuesday, December 26, 2023, 5:52 PM, Alek Petkovic via Amps <amps@...> wrote: Thanks for that information Lou and thanks to Doug for the leg work. Carl, along with Rich, Tom, Ian White, Tony King, yourself, Jim and lots of others are the ones that have fed me with knowledge, interest and enthusiasm in all things amplifiers over many, many years. 73, Alek VK6APK. On 27/12/2023 5:13 am, Louis Parascondola via groups.io wrote: > > > > Sent from the all new AOL app for iOS > <> > > Begin forwarded message: > > On Tuesday, December 26, 2023, 3:43 PM, Rudy Bakalov > < r_bakalov@...> wrote: > > > >? ? ----- Forwarded Message ----- >? ? *From:* Doug Grant < dougk1dg@...> >? ? *To:* YCCC < [email protected]> >? ? *Sent:* Tuesday, December 26, 2023 at 03:38:10 PM EST >? ? *Subject:* [yccc] Followup: KM1H > >? ? Since nobody had any direct info on Carl's status, I drove to his >? ? house and knocked on the door today, not quite sure what to expect. > >? ? Carl's ex-wife answered the door and invited me in. She announced >? ? me to Carl, who then made his way down the stairs . We had a nice >? ? visit and yakked for about a half-hour. He knew me, and even asked >? ? how my "twin" (K1AR) was doing. > >? ? He was unaware that his ham license had expired, but at age 83, >? ? sometimes events like that slip by. > >? ? So now you know "...the rest of the story". > >? ? 73, > >? ? Doug K1DG >_______________________________________________ Amps mailing list Amps@...
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Re: Gi46b on 2m - Thermal drift problem
G'day Tim.
Check (physically and electrically) your plate blocking/coupling
capacitor very carefully. John, VK6JX, had the exact same problem
with his GS35B model 2m amp, using what looks to be the same
Russian capacitor.
Likewise, we thought it was some sort of thermal drift problem
and you are right, you can't follow the rapid drop by adjusting
the tuning. It is too quick and you never catch up.
His 2200pF/10kV capacitor failed on the very first key down and
it was not obvious at all, until he removed it and looked at it
with a magnifier lens. There was a hairline crack and a little
blackening in the ceramic from the failure. I suspect that those
caps are not happy at 144MHz.
Good luck and 73, Alek VK6APK
On 26/12/2023 8:43 pm, Tim Fern wrote:
toggle quoted message
Show quoted text
Hi Everyone,
I built this little 2m amp a couple of years ago, it works
perfectly in every way..... except for the thermal drift.
Tuned up with key down, 300W out with 12W drive, within a few
seconds it droops to under 150W.
Keeping the power up requires *constant* re-tuning of the plate.
The drift is so fast I think it must be within the tube or close
to it, there just isn't time for the tank circuit to heat up.
I don't know if I made a mistake in the engineering of the tank
circuit, or if the tube is faulty
Open to all ideas about how to fix it.
Thanks
Tim G4LOH
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Re: Fw: [yccc] Followup: KM1H
Thanks for that information Lou and thanks to Doug for the leg
work.
Carl, along with Rich, Tom, Ian White, Tony King, yourself, Jim
and lots of others are the ones that have fed me with knowledge,
interest and enthusiasm in all things amplifiers over many, many
years.
73, Alek VK6APK.
On 27/12/2023 5:13 am, Louis
Parascondola via groups.io wrote:
toggle quoted message
Show quoted text
Begin forwarded message:
On Tuesday, December 26, 2023, 3:43 PM, Rudy Bakalov
<r_bakalov@...> wrote:
----- Forwarded Message -----
Sent: Tuesday, December 26, 2023 at 03:38:10
PM EST
Subject: [yccc] Followup: KM1H
Since nobody had any direct info on Carl's
status, I drove to his house and knocked on the
door today, not quite sure what to expect.
Carl's ex-wife answered the door and invited
me in. She announced me to Carl, who then made
his way down the stairs . We had a nice visit
and yakked for about a half-hour. He knew me,
and even asked how my "twin" (K1AR) was doing.
He was unaware that his ham license had
expired, but at age 83, sometimes events like
that slip by.
So now you know "...the rest of the story".
73,
Doug K1DG
|
Re: AL80B Smells Hot on 10M and 160M
This amp was made in 2001 indicated by 11-01 all over the inside of the amp.? No Heat on the Plate Choke.? Looks bright red all over.? I see no cracked caps at all neither.? I just had time to take it apart.? Any other areas of interest.? I have it apart and unplugged.
Thanks, Scott
On Mon, Dec 18, 2023 at 2:07?PM Steve < k0xp@...> wrote:
On 12/18/2023 9:35 AM, W7WRX wrote:
Those are Z5U caps.? They are a poor choice for coupling RF with
high current..? No wonder they failed.? Can't believe Alpha
would do that. I have repaired several 8410s and I don't even
remember those blue caps being used.
They done it; here's the BOM listing:
2 CDX-2221-C 3 C1-2 C7 CAP,CERAMIC DISK,0022uF,6KV 20% VISHAY
Here's the actual parts listing:
CDX-?‐2221-?‐C 3 CAP 2200PF 6K VOLTS 20% .375 L.S. RADIAL
I don't know the vintage of my amp, but it's early enough that it
had the VTX-118s in it. I've since bought a pair of 1500s but
haven't installed them yet.
?Really should use a cap that is rated for high RF current.? The
idea of using six caps for coupling is just bizarre.
I agree; I was flabbergasted when I first saw disc ceramics being
used as the plate blocking cap in a high power amplifier in my
ALS-800 (in fact, they, too, are blue, just like the Alpha's caps;
must be something about blue disc ceramic caps that is attractive
like a Siren to amplifier designers? 8-D ); it has a pair of
something, I didn't note what they were. I looked in the parts
list and schematic but I didn't note whether those are changed for
the ALS-800H, which uses a pair of -800A7s for well over
legal-limit output power. I doubt they are, though.
Rember: that guy -JI designed the ALS-800/800H, so it's GOTTA be
"right", right??? 8-D
?
I get that you had them but heck man.? Just order a proper HEC
high energy RF cap and be done with it.? The amp will work
better and be more reliable.
Perhaps. I've had quite a few of those CDE doorknobs that cracked,
though, so I'd probly use one of my few Russian humungously-sized
replacements, instead. However, the layout around that area is
tight, so there's not much room for a larger cap of any type without
lenthening the leads from the plate choke to the input tuning C. I
frankly was not very impressed with the layout of the 8410's output
section at all. I'm really wondering if the 160m coil's toroids are
going to do the same melting-stunt that I've read that K1TTT's
Commander HF-2500s have done during a contest.
By
the way,? Filament voltage on that 8410 should be checked!? They
run very high Fil voltage and if your line voltage hits 250 it
could pop those tubes.? I know this because one guy kept losing
4cx1000s.? We found he had high line voltage due to the entire
neighborhood being on Solar. In the middle of the day it would
hit 260!!? Then Pop the tubes.
I've gotta go do that ASAP; it seems to me that I might be losing
a bit of power every time I turn on this thing, which could be
from the cathodes boiling away and losing emission. I'm totally
off-the-grid here, and presently have to run the Alpha from a 3700
watt Xantrex RS3000M 120VAC inverter, which runs off six
paralleled 105 A/hr LiFePO4 batteries, recharged from 2 kW of
solar panels. I've measured the inverter's output at 124VAC under
800VA load but that drops to about 118 under 2 kVA load at the AC
outlet. Obviously, that is still too high for the Alpha since it
spends the majority of its time just idling. But there's no way to
turn it down unless I get out my 2.4 kVA variac. That Alpha is a
power hog, though... I can't usually run a pileup longer than a
few hours before the batteries drop below 50% State-Of-Charge,
which, on a cloudy day, might get back up into the high 80s by
sundown the next day. I've had it down to 14% (right after the
recent ARRL 160m contest) but that day was bright and sunny, so
the batts got recharged back to about 75% by sundown.
73,
Steve K0XP
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Gi46b on 2m - Thermal drift problem
Hi Everyone, I built this little 2m amp a couple of years ago, it works perfectly in every way..... except for the thermal drift. Tuned up with key down, 300W out with 12W drive, within a few seconds it droops to under 150W. Keeping the power up requires *constant* re-tuning of the plate. The drift is so fast I think it must be within the tube or close to it, there just isn't time for the tank circuit to heat up. I don't know if I made a mistake in the engineering of the tank circuit, or if the tube is faulty Open to all ideas about how to fix it. Thanks Tim G4LOH  
|
Fw: [yccc] Followup: KM1H
toggle quoted message
Show quoted text
On Tuesday, December 26, 2023, 3:43 PM, Rudy Bakalov <r_bakalov@...> wrote:
----- Forwarded Message -----
From: Doug Grant <dougk1dg@...> Sent: Tuesday, December 26, 2023 at 03:38:10 PM EST Subject: [yccc] Followup: KM1H
Since nobody had any direct info on Carl's status, I drove to his house and knocked on the door today, not quite sure what to expect.
Carl's ex-wife answered the door and invited me in. She announced me to Carl, who then made his way down the stairs . We had a nice visit and yakked for about a half-hour. He knew me, and even asked how my "twin" (K1AR) was doing.
He was unaware that his ham license had expired, but at age 83, sometimes events like that slip by.
So now you know "...the rest of the story".
73,
Doug K1DG
|
Re: Building my first amplifier. Where to start?
With 3 phases anode voltage will be completely different as will be the rectifier stack.
?
73
Peter, DJ7WW
?
?
?
-----Original-Nachricht-----
Betreff: Re: [ham-amplifiers] Building my first amplifier. Where to start?
Datum: 2023-12-26T18:56:37+0100
Von: "desmond auld" <desauld@...>
An: "[email protected]" <[email protected]>
?
?
?
Hal,
I might message g(m)0sek if I struggle,thanks for the advice.??
I have a 3 phase transformer with various taps. It's rated 20kva. I have tried single phasing it, and it runs ok. Less capacity obviously but it has plenty to spare. It's circa 150kg or 330lb. Depending on the configuration I have various output voltages. If needed I have 3 phase from a genset available.? Anode supply shouldn't be an issue.?
?
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Re: Building my first amplifier. Where to start?
On 12/26/2023 9:56 AM, desmond auld wrote: I have a 3 phase transformer with various taps. It's rated 20kva. I have tried single phasing it, and it runs ok. Less capacity obviously but it has plenty to spare. It's circa 150kg or 330lb. Depending on the configuration I have various output voltages. If needed I have 3 phase from a genset available.? Anode supply shouldn't be an issue. Ummm... before you settle on that monster, you might want to fire her up and measure the idling current, no-load. Then again, with some temporary load resistors across the secondary. The results just might make you wonder if you aren't mad... 8-) Steve, K0XP
|
Re: Building my first amplifier. Where to start?
First thing I'd do is copy the spreadsheet and revise the dropped
Ep to no more than 2500V, perhaps 2550 at most, then design for
that reduced value. Unless you're in a commercial establishment,
with commercial-quality mains and components, Ep always seems to
drop below our best hopes? 8-/
Steve, K0XP
On 12/26/2023 8:05 AM, desmond auld
wrote:
Hal,
Yes, one of concerns is "committing" to a tube that dries up by
way of availability.? That's why the GS35 and Gu43b are on my
radar,as they seem so plentiful.? If i do get an amplifier up and
running of my own creation i will invest in many spares to keep on
the shelf and circulate every year to keep fresh ish.? The old
811's in my existing amp has are now getting relatively expensive
for a 65w dissipation tube,and the 572B's are out of hand cost
wise considering they are all now Chinese of poor/average quality,
so i understand the concern of going down a dead end.??
I have spent some time today reading, and plugging in numbers into
the wonderful G3SEK spreadsheet to calculate the values of C1, C2
and L1 in the tank circuit of an imaginary amplifier based around
two GU43b's in parallel. I have assumed some things, obviously,
like the HV will drop under load to 2700vdc from circa 2900vdc.? I
have modified the spreadsheet to have a tab for each band, 10-80m,
that i'm interested in, and also a summary sheet with what a
beginner such as myself thinks is important.? i would be VERY
grateful if those that know what they are doing could critique my
assumptions and the outputs.? Spreadsheet attached , with summary
copied in below.
Does anything look way out of wack in my assumptions, or not
practically possible in my outputs?
I went looking in my "capacitors for the big amplifier" box and
have a good section of high voltage door knobs, and two beautiful
vacuum variables, that i could use.? One is very large, 25KV rated
15-350pf, and another is smaller 15-90 pf 40Kv rated.? I had
almost forgot i had these things!? I'm getting quite excited. :)?
Has anyone any good links for winding tank coils with calculations
etc??
Alex from UR4LL has the GU43b tubes in stock and i am talking to
him at the moment about purchasing some along with some other
parts i may need.? He has a beautiful EImac 4cx 10,000 for sale if
anyone is interested.? I'm not man enough :)
Thanks guys
--
See my QRZ.com page at
|
Re: Building my first amplifier. Where to start?
|
Re: Building my first amplifier. Where to start?
Hi Desmond,
?
What is your Ham Radio Call Sign?
?
Thanks,
?
Walter
KR4HV
?
toggle quoted message
Show quoted text
From: [email protected] <[email protected]>
On Behalf Of desmond auld
Sent: 26 December, 2023 12:48 PM
To: [email protected]
Subject: Re: [ham-amplifiers] Building my first amplifier. Where to start?
?
Peter,
Thanks for the advice. Ok, I understand the issue can be stray capacitance and inductance?
I see this project happening in stages, eg build with what I have and some extra pieces to prove the concept and learn. Then refine the build and make tidy, using more suitable components etc.? Never make the prototype the final example is my thinking.
Thanks, des.?
|
Re: Building my first amplifier. Where to start?
Hal,
I might message g(m)0sek if I struggle,thanks for the advice.??
I have a 3 phase transformer with various taps. It's rated 20kva. I have tried single phasing it, and it runs ok. Less capacity obviously but it has plenty to spare. It's circa 150kg or 330lb. Depending on the configuration I have various output voltages. If needed I have 3 phase from a genset available.? Anode supply shouldn't be an issue.?
|
Re: Building my first amplifier. Where to start?
Peter,
Thanks for the advice. Ok, I understand the issue can be stray capacitance and inductance?
I see this project happening in stages, eg build with what I have and some extra pieces to prove the concept and learn. Then refine the build and make tidy, using more suitable components etc.? Never make the prototype the final example is my thinking.
Thanks, des.?
|
Re: Building my first amplifier. Where to start?
Des,
?
GM3SEK relocated to Scotland some years ago.
I believe he will still correspond with amateurs
who face design complications.
?
I still would like to know what your power supply
might consist of.
?
The Anode trannie is so important. The last
thing you want to face is the voltage sag while keying.
?
So have you made your decision? I believe you
mentioned having a retired “Pole pig.”
?
They are so worthwhile.
?
Hal
|
Re: Building my first amplifier. Where to start?
I would use capacitors as small as possible, not those monsters.
You want all connections within the tank circuitry as short as possible.
?
I have good experience winding coils by using the program PIEL:
?
73
Peter, DJ7WW
?
?
?
?
-----Original-Nachricht-----
Betreff: Re: [ham-amplifiers] Building my first amplifier. Where to start?
Datum: 2023-12-26T17:05:56+0100
Von: "desmond auld" <desauld@...>
Does anything look way out of wack in my assumptions, or not practically possible in my outputs?
I went looking in my "capacitors for the big amplifier" box and have a good section of high voltage door knobs, and two beautiful vacuum variables, that i could use.? One is very large, 25KV rated 15-350pf, and another is smaller 15-90 pf 40Kv rated.? I had almost forgot i had these things!? I'm getting quite excited. :)?
Has anyone any good links for winding tank coils with calculations etc??
?
|
Re: Building my first amplifier. Where to start?
Hal, Yes, one of concerns is "committing" to a tube that dries up by way of availability.? That's why the GS35 and Gu43b are on my radar,as they seem so plentiful.? If i do get an amplifier up and running of my own creation i will invest in many spares to keep on the shelf and circulate every year to keep fresh ish.? The old 811's in my existing amp has are now getting relatively expensive for a 65w dissipation tube,and the 572B's are out of hand cost wise considering they are all now Chinese of poor/average quality, so i understand the concern of going down a dead end.?? I have spent some time today reading, and plugging in numbers into the wonderful G3SEK spreadsheet to calculate the values of C1, C2 and L1 in the tank circuit of an imaginary amplifier based around two GU43b's in parallel. I have assumed some things, obviously, like the HV will drop under load to 2700vdc from circa 2900vdc.? I have modified the spreadsheet to have a tab for each band, 10-80m, that i'm interested in, and also a summary sheet with what a beginner such as myself thinks is important.? i would be VERY grateful if those that know what they are doing could critique my assumptions and the outputs.? Spreadsheet attached , with summary copied in below.  Does anything look way out of wack in my assumptions, or not practically possible in my outputs? I went looking in my "capacitors for the big amplifier" box and have a good section of high voltage door knobs, and two beautiful vacuum variables, that i could use.? One is very large, 25KV rated 15-350pf, and another is smaller 15-90 pf 40Kv rated.? I had almost forgot i had these things!? I'm getting quite excited. :)? Has anyone any good links for winding tank coils with calculations etc?? Alex from UR4LL has the GU43b tubes in stock and i am talking to him at the moment about purchasing some along with some other parts i may need.? He has a beautiful EImac 4cx 10,000 for sale if anyone is interested.? I'm not man enough :) Thanks guys
|
Re: Building my first amplifier. Where to start?
Was discussed some years ago on the amps reflector:
?
?
Its a low ? generator tube with poor iMD and high drive requirements.
?
73
Peter, DJ7WW
?
?
?
-----Original-Nachricht-----
Betreff: Re: [ham-amplifiers] Building my first amplifier. Where to start?
Datum: 2023-12-26T11:55:02+0100
Von: "Jim VE7RF" <jim.thom@...>
An: "[email protected]" <[email protected]>
?
?
?
How do u now the GU5B? only has 10 db of gain ???
?
|
Re: Building my first amplifier. Where to start?
Dear Des,
?
Some years ago I invested money into whar was then a seemingly up-and-coming amplifier that used a GU-78b.
?
The first thing I did when setting the amplifier up
was to seek out a spare tube.
?
Some friends of mine in the former Soviet Military
were all too willing to scour the shelves looking for
a spare for me, but alas, there were none apparent.
?
I would say now these ‘78’s are as rare as
Stanley Steamer 3CV1500A7’s, and to steer clear
of building something around one.
?
(In my foolishness my last unfinished QRO project
centered around a pair of GU-84b’s, still in their
Svetlana sealed factory styrofoam cartons.)
?
But even these monsters are getting rarer and rarer.
?
However the ‘35’s are still readily available, and they
make a wonderful combo for easily-driven Cathode
valves.
?
Hal Mandel
W4HBM
|
Re: Building my first amplifier. Where to start?
Jim,
I found a reference on the net to someone who has build an amplifier around the GU5b some time agai and he stated gain was low and required 200w drive to maximise output.?
Here is a link to the datasheet if that helps.
What's your thoughts on gu43b's? Also what is the calculation you referenced to approximate input impedance? Thanks,des
|
HaL Mandel
