Tim and anyone interested :
Here’s looking inside the RF box. You can see the original blocking cap - just like yours ! This is a YU1AW “Lazy Builder” design. Suited my construction capabilities perfectly !
You can see the thick Teflon sheet insulation between the tune (right) and the”load” caps. I was so dumb back then, I thought I could adjust the loading like a HF triode amp. As Lou said, we all still learning about amps.
The lower pic shows the RF box inside the amp cabinet. The large blower feeding cooling air into the bottom of the RF box, Russki REW14 input and output relays, many 6A10 diodes for operating bias, toroidal filament tranny, metering, etc. are visible.
The only other stuff up I made was not using proper terminated cables for the input and output N-Type connectors. I’ll fix that soon.
Good luck with it, and let us know how you go.
Cheers,
John VK6JX
|
Tim - here’s what happened to my 2200pF blocking cap. Cracked and a little burnt. This caused ALL of the “thermal” power output drift in my 2m amp. She’s rock solid now, for complete JT65B overs. Love it !
John
|
Re: Gi46b on 2m - Thermal drift problem
No probs. An even better option, if your tank is well insulated (as mine is) is to remove the blocking cap entirely and connect the anode directly to the tank. I used large Teflon standoff posts and thick Teflon sheet as you have everywhere, so there are no issues with HV on the tank. John
toggle quoted message
Show quoted text
On 27 Dec 2023, at 21:02, Tim Fern <timjfern@...> wrote:
?Thanks!
I'm down with COVID right now, the junkbox has some other Ceramic button caps, I switch it out in a few days and let you know how I got on.
vy73
Tim
|
Re: Building my first amplifier. Where to start?
The G2 volt is 850V， yes， very large G2 current, hundreds milliampre??
? ?Hsu Steve < k0xp@...> 于2023年12月28日周四 04:08写道：
Hsu, what g2 did you use? It seems as though the GU-81M consumes
a LOT of g2 current, too...
73 & HNY,
Steve K0XP
On 12/27/2023 11:54 AM, Hsu wrote:
It seems that the GU-81M is what you want. I just
built an amplifier using a pair of FU-81/FM-8 (GU-81M/GI-8) with
output power: 1.8-14MHz, 2900W, 21-28Mhz, 2500W.grid driven, if
you only want 1KW, you can use one GU-81M on grunded-grid with a
power gain of about The GU-81M has a large
output capacitance, the plate capacitor must be replaced with a
fixed capacitor and requires a roller inductor to tune, and at
21MHz and higher, the plate capacitor C1 is replaced by the
output capacitor, as the EX8A does.?The amplifier is very quiet
and requires little to no heating time, and the tubes are very
inexpensive
? ? ? ?Hsu
desmond auld GI0UTE < desauld@...>
于2023年12月27日周三 16:32写道：
Peter,
You are of course correct. But due to the tappings I have
options to get the voltage to where I want. The rectifier and
the DC produced would be better if I settled on 3 phase, but I
prefer this to be a plan b at this stage.
Thanks des?
--
See my QRZ.com page at
|
Re: Building my first amplifier. Where to start?
Hsu, what g2 did you use? It seems as though the GU-81M consumes
a LOT of g2 current, too...
73 & HNY,
Steve K0XP
On 12/27/2023 11:54 AM, Hsu wrote:
It seems that the GU-81M is what you want. I just
built an amplifier using a pair of FU-81/FM-8 (GU-81M/GI-8) with
output power: 1.8-14MHz, 2900W, 21-28Mhz, 2500W.grid driven, if
you only want 1KW, you can use one GU-81M on grunded-grid with a
power gain of about The GU-81M has a large
output capacitance, the plate capacitor must be replaced with a
fixed capacitor and requires a roller inductor to tune, and at
21MHz and higher, the plate capacitor C1 is replaced by the
output capacitor, as the EX8A does.?The amplifier is very quiet
and requires little to no heating time, and the tubes are very
inexpensive
? ? ? ?Hsu
desmond auld GI0UTE < desauld@...>
于2023年12月27日周三 16:32写道：
Peter,
You are of course correct. But due to the tappings I have
options to get the voltage to where I want. The rectifier and
the DC produced would be better if I settled on 3 phase, but I
prefer this to be a plan b at this stage.
Thanks des?
--
See my QRZ.com page at
|
Re: Building my first amplifier. Where to start?
It seems that the GU-81M is what you want. I just built an amplifier using a pair of FU-81/FM-8 (GU-81M/GI-8) with output power: 1.8-14MHz, 2900W, 21-28Mhz, 2500W.grid driven, if you only want 1KW, you can use one GU-81M on grunded-grid with a power gain of about The GU-81M has a large output capacitance, the plate capacitor must be replaced with a fixed capacitor and requires a roller inductor to tune, and at 21MHz and higher, the plate capacitor C1 is replaced by the output capacitor, as the EX8A does.?The amplifier is very quiet and requires little to no heating time, and the tubes are very inexpensive ? ? ? ?Hsu desmond auld GI0UTE < desauld@...> 于2023年12月27日周三 16:32写道：
Peter,
You are of course correct. But due to the tappings I have options to get the voltage to where I want. The rectifier and the DC produced would be better if I settled on 3 phase, but I prefer this to be a plan b at this stage.
Thanks des?
|
Re: Building my first amplifier. Where to start?
Des,
?
Ian’s callsign is GM3SEK.
?
When I was involved in Underground Coal Mining many of the
Vehicles ran on 3 phase a.c., with stout umbilical cords connecting
To 4160, 3-Ph distribution xfmrs dragged along on skids,
With numerous outlets for 480, 960, etc.
?
Why not see if you can dismember your 3-Ph XFMR and wind the
Primaries, etc, in parallel for a 240 input and extra oomph
On the outputs?
?
Hal
|
Re: Building my first amplifier. Where to start?
I would have to disagree with the 2500V in the case of the GS35
specifically.? To get 1.5KW out, I think the Ig will be too high
at that low of a voltage.??
I ran 4300V on mine and that was very nice from a minimal Ig
standpoint although I think 3500V may be the sweet spot
compromise.? The tube spec is 3KV CCS and 6KV pulse.? Of course
with any proposed tube you want to use, getting a check with a
suitable BDV tester is going to be step one.??
An additional benefit of the higher HV::? The Soviet tubes in
general tend to be a bit less gain than the Eimac and the higher
voltage will help with the gain as well.
73/jeff/ac0c
alpha-charlie-zero-charlie
On 12/26/2023 2:15 PM, Steve wrote:
toggle quoted message
Show quoted text
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: Gi46b on 2m - Thermal drift problem
Thanks!
I'm down with COVID right now, the junkbox has some other Ceramic button caps, I switch it out in a few days and let you know how I got on.
vy73
Tim
|
Re: [Amps] [ham-amplifiers] Fw: [yccc] Followup: KM1H
Hi John, hope you had a Merry Christmas and do have a Happy New Year.
On Wednesday, December 27, 2023, 2:21 AM, John Sparkes via groups.io <vk6jx@...> wrote: Ha ha ! We sure are, Lou ! Some of us, learn a lot from you guys. BTW, my W1QJ converted SB220 6m amp works bloody well. The Japs don’t know what’s hit them !! Happy new year to all. John VK6JX On 27 Dec 2023, at 07:58, Louis Parascondola via groups.io <Gudguyham@...> wrote:
?
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@...
|
Re: Building my first amplifier. Where to start?
Peter,
You are of course correct. But due to the tappings I have options to get the voltage to where I want. The rectifier and the DC produced would be better if I settled on 3 phase, but I prefer this to be a plan b at this stage.
Thanks des?
|
Re: Building my first amplifier. Where to start?
Steve,
I haven't measured idle current of the transformer so I will do that when I dig it out from long term storage. To be fair, even if it idles absorbing a 1kw, which I doubt, I only get maybe 8 hours max per week to "ham" so it's not such a big issue.?
The 3cw 30,000 uses 1kw on the filament alone, so wasted power is all relative:) .
I take your point on rerunning the spreadsheet at reduced voltage level, so I will do that.?
Thanks des?
|
Re: Gi46b on 2m - Thermal drift problem
Hi Tim. Yeah, those big caps are no good on 2m ! She works great now with a smaller value cap. Rock solid power out. John VK6JX
toggle quoted message
Show quoted text
On 27 Dec 2023, at 07:19, Alek Petkovic via groups.io <vk6apk@...> wrote:
?
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:
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
|
Re: [Amps] [ham-amplifiers] Fw: [yccc] Followup: KM1H
Ha ha ! We sure are, Lou ! Some of us, learn a lot from you guys. BTW, my W1QJ converted SB220 6m amp works bloody well. The Japs don’t know what’s hit them !! Happy new year to all. John VK6JX
toggle quoted message
Show quoted text
On 27 Dec 2023, at 07:58, Louis Parascondola via groups.io <Gudguyham@...> wrote:
?
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@...
|
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! :)
|
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@...
|
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
|
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
|
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  
|
HaL Mandel