I just remembered the company, it was Sola and the product is/was the Constant Voltage Transformer. Looked on ebay and there's quite a few listed with a wide range of characteristics.
On Mon, Oct 16, 2023 at 4:10?PM John W Cress via <johnk0gcj= [email protected]> wrote: Years ago there was a company that produced a regulating 1:1 or 2:1 transformer with a ferro-resonant winding. hTeret had a capacitor across to hold the voltage steady. I don't know the specifics of it's performance; and don't? remember the name of the company nor the name of the product, but they were quite prevalent in industry and remember them?being in demand by hams back then. It's probably been 30 or 40 years since hearing the name.
John K0GCJ
On Mon, Oct 16, 2023 at 2:08?PM HaL Mandel < hmandel@...> wrote:
Gents, One of the bug-a-boos about QRO
tubism is the regulation and acceptability
of filament voltages.
?
Okay, tube manufacturers tell us “10%,”
and we have to live with whatever
Con Edison or Kentucky Power ends up
at our QTH to ply our signals out and about.
?
I know, I know Continental and all them
have Buck’n’boosters, automated
variacs on 3-phase mains: Just everything
money can buy.
?
So here’s Dave saying his filament voltage
droops a bit, and I’m sure there are others
out there, running 8877’s or CPX’s and
other thoriated devices, and what can we
as technicians offer them?
?
Would it not be fabulous for QST to publish in
its last edition this December, a sure-fire and
affordable means to conquer filament squirrels?
?
Let’s say Joe Ham has a wonderful $6K to $10K
linear running tubes that are in need of regulation.
Would it not be remiss to afford 10% more for a
regulation gizmo??
?
I know how much a good set of finals cost, and
frankly, I don’t know if I can ante up for a new
set if I pop the ones I got right now.?
?
So like owning a car that’s beginning to use a bit
more oil, I keep the drive down a bit on my inputs,
and just hope the beast can gently grow old like
the old man.
?
Hal
W4HBM
|
Years ago there was a company that produced a regulating 1:1 or 2:1 transformer with a ferro-resonant winding. hTeret had a capacitor across to hold the voltage steady. I don't know the specifics of it's performance; and don't? remember the name of the company nor the name of the product, but they were quite prevalent in industry and remember them?being in demand by hams back then. It's probably been 30 or 40 years since hearing the name.
John K0GCJ
On Mon, Oct 16, 2023 at 2:08?PM HaL Mandel < hmandel@...> wrote:
Gents, One of the bug-a-boos about QRO
tubism is the regulation and acceptability
of filament voltages.
?
Okay, tube manufacturers tell us “10%,”
and we have to live with whatever
Con Edison or Kentucky Power ends up
at our QTH to ply our signals out and about.
?
I know, I know Continental and all them
have Buck’n’boosters, automated
variacs on 3-phase mains: Just everything
money can buy.
?
So here’s Dave saying his filament voltage
droops a bit, and I’m sure there are others
out there, running 8877’s or CPX’s and
other thoriated devices, and what can we
as technicians offer them?
?
Would it not be fabulous for QST to publish in
its last edition this December, a sure-fire and
affordable means to conquer filament squirrels?
?
Let’s say Joe Ham has a wonderful $6K to $10K
linear running tubes that are in need of regulation.
Would it not be remiss to afford 10% more for a
regulation gizmo??
?
I know how much a good set of finals cost, and
frankly, I don’t know if I can ante up for a new
set if I pop the ones I got right now.?
?
So like owning a car that’s beginning to use a bit
more oil, I keep the drive down a bit on my inputs,
and just hope the beast can gently grow old like
the old man.
?
Hal
W4HBM
|
Gents, One of the bug-a-boos about QRO
tubism is the regulation and acceptability
of filament voltages.
?
Okay, tube manufacturers tell us “10%,”
and we have to live with whatever
Con Edison or Kentucky Power ends up
at our QTH to ply our signals out and about.
?
I know, I know Continental and all them
have Buck’n’boosters, automated
variacs on 3-phase mains: Just everything
money can buy.
?
So here’s Dave saying his filament voltage
droops a bit, and I’m sure there are others
out there, running 8877’s or CPX’s and
other thoriated devices, and what can we
as technicians offer them?
?
Would it not be fabulous for QST to publish in
its last edition this December, a sure-fire and
affordable means to conquer filament squirrels?
?
Let’s say Joe Ham has a wonderful $6K to $10K
linear running tubes that are in need of regulation.
Would it not be remiss to afford 10% more for a
regulation gizmo??
?
I know how much a good set of finals cost, and
frankly, I don’t know if I can ante up for a new
set if I pop the ones I got right now.?
?
So like owning a car that’s beginning to use a bit
more oil, I keep the drive down a bit on my inputs,
and just hope the beast can gently grow old like
the old man.
?
Hal
W4HBM
|
Re: Symptom(s) for a fading 8877 tube?
Measured Voltage results of Alpha 9500 key down testing.
AC Mains Voltage at Amplifier switch box.
142 VAC Amp on at Standby.
239.6 VAC Amp at 1.3 KW into Dummy load
?
Filament Voltage
5.3 VAC at initial power on.
5.45 VAC after 180 Second warm up remains at 5.45 during subsequent Standby (not Transmitting).
5.16 VAC on Key Down 1.3 KW.
?
Plate Voltage
3.5 KV during any and all standby conditions.
3.2 KV during key down 1.3KW.
?
Looks like normal Voltages to me.? Strongly points to a weak tube.
?
Thank you, Alan and Alex for urging the Voltage tests.
Alan, the filament voltage check was really simple through the bottom plate.
Having two Fluke VOMs made this testing easy and less dangerous.—no having to move probe tips after set-up.
?
73,
Dave, w6de
?
toggle quoted message
Show quoted text
From: [email protected] < [email protected]>
On Behalf Of Alan - W5ARM via groups.io
Sent: 16 October, 2023 17:02
To: [email protected]
Subject: Re: [ham-amplifiers] Symptom(s) for a fading 8877 tube?
?
Hey Dave,
If your amp has been operating "normally" for a length of time (i.e., with apparently normal/full output) and only recently started showing signs of decreased power, then it's probably a bad tube.
However, it would be prudent to check your filament voltage, to ensure that it is within spec. If anything will kill an 8877 tube, it's LOW filament voltage.? An under-temp/cold cathode will cause striping of the coating off the cathode, dramatically shortening
its life. The filament voltage must be checked at the tube base, at both static (no load) and loaded (max RF) conditions.
Tom Rauch, W8JI, has documented this... it is worth the read. HERE:?? and HERE:
On the 9500, you can access the tube base by setting the amp over on its right side (viewing from the front), and removing the cover on the amp bottom, below the tube. Obviously, for safety: Do this with the amp unplugged, and be certain the B+ is fully discharged
(although no B+ voltage on the bottom). Make the connections to your meter, then plug-in the amp and power up. No harm in running the amp on its side for the short period of testing.
Connect a DVM to the filament pins, and then fire-up the amp. Allow the tube to come up to temperature (3 minutes), then make note the filament voltage. Then apply some drive and get RF output (preferably near legal-limit) and again make note of the filament
voltage.? If the filament voltage is NOT within specs, then there's an issue.
It's better to have slightly high voltage unloaded, and at or near specification (or slightly high) under load, than it is to have low voltage, especially under load.
While replacing your existing tube will likely cure the low RF output problem, continuing to run with low filament voltage will kill the new tube also, although it may take a while.
Just as a point of interest, my 9500 runs at closer to 3450-3500 volts on the plate, and my input line-voltage is always very close to 250v (247-249).
Good luck. Let us know what you find...
73,
~Alan
W5ARM
|
Re: Symptom(s) for a fading 8877 tube?
Hey Dave,
If your amp has been operating "normally" for a length of time (i.e., with apparently normal/full output) and only recently started showing signs of decreased power, then it's probably a bad tube.
However, it would be prudent to check your filament voltage, to ensure that it is within spec. If anything will kill an 8877 tube, it's LOW filament voltage.? An under-temp/cold cathode will cause striping of the coating off the cathode, dramatically shortening its life. The filament voltage must be checked at the tube base, at both static (no load) and loaded (max RF) conditions.
Tom Rauch, W8JI, has documented this... it is worth the read. HERE:?? and HERE:
On the 9500, you can access the tube base by setting the amp over on its right side (viewing from the front), and removing the cover on the amp bottom, below the tube. Obviously, for safety: Do this with the amp unplugged, and be certain the B+ is fully discharged (although no B+ voltage on the bottom). Make the connections to your meter, then plug-in the amp and power up. No harm in running the amp on its side for the short period of testing.
Connect a DVM to the filament pins, and then fire-up the amp. Allow the tube to come up to temperature (3 minutes), then make note the filament voltage. Then apply some drive and get RF output (preferably near legal-limit) and again make note of the filament voltage.? If the filament voltage is NOT within specs, then there's an issue.
It's better to have slightly high voltage unloaded, and at or near specification (or slightly high) under load, than it is to have low voltage, especially under load.
While replacing your existing tube will likely cure the low RF output problem, continuing to run with low filament voltage will kill the new tube also, although it may take a while.
Just as a point of interest, my 9500 runs at closer to 3450-3500 volts on the plate, and my input line-voltage is always very close to 250v (247-249).
Good luck. Let us know what you find...
73,
~Alan
W5ARM
|
Re: High filament current on the 8877 amplifier tube
And a "soft" tube acts as a soft fuse.
W4DNR? ? ? ? ??
toggle quoted message
Show quoted text
On 2023-10-16 10:35 am, Mike Sawyer via groups.io wrote:
I bought one off of Ebay once for about $30. The seller claimed it had low output. It didn't matter to me because at the time I was contemplating building an amp with one of them. My elmer Eric, WB4VVI(SK) always insisted on using a tube with low or no output to test the HV section and grid drive section. That way if you missed something during your construction and an 'event' happens during the testing phase, you will have ruined a tube of little value as opposed to a new or one with full output.
?
Mod-U-Lator,
Mike(y)/W3SLK
?
?
?
?
The duds could be eye candy for one's shack.? Maybe put them on QRZ, etc.
Andy? K9ATX
On 10/16/2023 1:46 AM, Tim Duffy K3LR wrote:
I am still testing 8877s here. Two or three every day. They warm up with filament only for 4 hours before HV.
What I have learned is that 8877's drawing 15 amps of filament current are bad tubes. They draw zero plate current.
So the five tubes that are high filament current ones, are "duds"
?
So what is the proper way to dispose of these bad tubes?
?
73
Tim K3LR
?
?
Most 8877 tubes that I test draw 11 amps of filament current at 5 volts.
I have tested three recently that draw 15 amps of filament current. All of these tubes are used and have little "dings".
?
Is 15 amps an indication of a problem tube? Or should I apply HV to the plate and see what happens?
?
73
Tim K3LR
--
"Where the Old Soo crossed the New Soo"
Duplainville, Wisconsin
?
Web page:?
?
Youtube Channel:?
|
Re: High filament current on the 8877 amplifier tube
I bought one off of Ebay once for about $30. The seller claimed it had low output. It didn’t matter to me because at the time I was contemplating building an amp with one of them. My elmer Eric, WB4VVI(SK) always insisted on using a tube with low or no output to test the HV section and grid drive section. That way if you missed something during your construction and an ‘event’ happens during the testing phase, you will have ruined a tube of little value as opposed to a new or one with full output. ? Mod-U-Lator, Mike(y)/W3SLK ? ? ?
toggle quoted message
Show quoted text
From: [email protected] [mailto:[email protected]] On Behalf Of DupyRail
Sent: Monday, October 16, 2023 10:22 AM
To: [email protected]
Subject: Re: [ham-amplifiers] High filament current on the 8877 amplifier tube? The duds could be eye candy for one's shack.? Maybe put them on QRZ, etc.
Andy? K9ATX
On 10/16/2023 1:46 AM, Tim Duffy K3LR wrote: I am still testing 8877s here. Two or three every day. They warm up with filament only for 4 hours before HV. What I have learned is that 8877’s drawing 15 amps of filament current are bad tubes. They draw zero plate current. So the five tubes that are high filament current ones, are “duds” ? So what is the proper way to dispose of these bad tubes? ? 73 Tim K3LR ? ? Most 8877 tubes that I test draw 11 amps of filament current at 5 volts. I have tested three recently that draw 15 amps of filament current. All of these tubes are used and have little “dings”. ? Is 15 amps an indication of a problem tube? Or should I apply HV to the plate and see what happens? ? 73 Tim K3LR
-- "Where the Old Soo crossed the New Soo" Duplainville, Wisconsin ? Web page:? ? Youtube Channel:?
|
Re: High filament current on the 8877 amplifier tube
The duds could be eye candy for one's shack.? Maybe put them on QRZ,
etc.
Andy? K9ATX
On 10/16/2023 1:46 AM, Tim Duffy K3LR
wrote:
I am still
testing 8877s here. Two or three every day. They warm up
with filament only for 4 hours before HV.
What I have
learned is that 8877’s drawing 15 amps of filament current
are bad tubes. They draw zero plate current.
So the five
tubes that are high filament current ones, are “duds”
?
So what is the
proper way to dispose of these bad tubes?
?
73
Tim K3LR
?
?
Most 8877 tubes that I test draw 11 amps of
filament current at 5 volts.
I have tested three recently that draw 15
amps of filament current. All of these tubes are used and have
little “dings”.
?
Is 15 amps an indication of a problem tube?
Or should I apply HV to the plate and see what happens?
?
73
Tim K3LR
--
"Where the Old Soo crossed the New Soo"
Duplainville, Wisconsin
Web page:
Youtube Channel:
|
Re: High filament current on the 8877 amplifier tube
I am still testing 8877s here. Two or three every day. They warm up with filament only for 4 hours before HV. What I have learned is that 8877’s drawing 15 amps of filament current are bad tubes. They draw zero plate current. So the five tubes that are high filament current ones, are “duds” ? So what is the proper way to dispose of these bad tubes? ? 73 Tim K3LR ?
toggle quoted message
Show quoted text
From: Tim Duffy [mailto:k3lr@...]
Sent: Sunday, October 8, 2023 2:48 PM
To: '[email protected]'; 'amps@...'
Subject: High filament current on the 8877 amplifier tube? Most 8877 tubes that I test draw 11 amps of filament current at 5 volts. I have tested three recently that draw 15 amps of filament current. All of these tubes are used and have little “dings”. ? Is 15 amps an indication of a problem tube? Or should I apply HV to the plate and see what happens? ? 73 Tim K3LR
|
Re: Symptom(s) for a fading 8877 tube?
Yes,? when shop/shack was constructed, I specified the wiring as #10 and multiple 240 outlets each on separate breakers (according to code) and over saw the construction and wiring.? I know if it was constructed properly, I don’t know if
I have a current problem, but I checked the wall socket before connecting the Alpha earlier this year. ??I also have a 240 volt two wire motor switch for each 240 VAC outlet and I checked the voltage there also when I installed 20 amp fused in the switch box.
?
I’ll open the switch box and check later when it is under load.
?
Thanks for asking.
?
Dave, w6de
?
toggle quoted message
Show quoted text
From: [email protected] < [email protected]>
On Behalf Of Alek Petkovic via groups.io
Sent: 15 October, 2023 21:54
To: [email protected]
Cc: aa6yq@...
Subject: Re: [ham-amplifiers] Symptom(s) for a fading 8877 tube?
?
Hi Dave.
My question is about your AC mains supply. Is it up to the task?
Section 3.2 and table 3-1 talk about what you can expect from different mains supplies.
Also, I looked in the manual to see if they mentioned the anode voltage but found no mention of it. Is 3200V the correct voltage and what does it sag to on key down? Excessive sag will also affect your heater voltage.
The Eimac datasheet says 1085W out at 2700V anode voltage.
Look at all the above before you go changing the tube.
73 and good luck, Alek VK6APK.
On 15/10/2023 7:21 am, Dave w6de wrote:
Good point, if the cathode emission is down, there aren’t enough electrons being ejected from the cathode to make the higher power levels.? Time to switch tubes.? Since this amplifier case is already full and I have a spare tube, ?I’m not
going to hack it up to make the filament voltage adjustable.?
But I going to wait until after the bands quiet down. ?Right now, I don’t want to side-line the Alpha 9500 for my first time (with this amplifier) tube replacement and de-gassing cook in.
?
73,
Dave, w6de
?
?
?
If the tube is half in the grave, Increasing Filament voltage and current to increase emission from the remaining cathode carbon may help until the end ?
?
73
?
vk4tux
On 14/10/23 14:21, Dave w6de wrote:
I have an Alpha 9500 and I find it difficult to get 1500 Watts out of the current Thompson 8877--age unknown.
The symptom is: I can easily get 1,000 to 1,100 Watts out of the amplifier but continuing to increase the drive level (to get power above 1.3KW) power output does not continue its somewhat linear increase in power output.?
I reach a level where I am concerned about increasing the drive because I don't see increase in output power.? And the grid current is reaching 90 Milliamps where I stop trying.
There is 3,200 Volts on the Plate and the plate current won't increase above ≈ 0.7 amps without exceeding grid current limits. Running class AB2 a linear is about 60% efficiency I should be getting about 1,344 Watts and I'm seeing 1370 Watts on the built-in
power meter which matches my Bird power meter pretty closely.? But When I try to increase the drive, the amplifier will momentarily indicate 1500 watts but immediately drop back to 1300 watts.
All testing into a large surplus 50 Ohm dummy load.
Side Note: the Alpha 9500 has automatic tuning of the plate/output circuit.? I leave it on as I do several band and mode changes during an operating session.? And I and use a Steppir antenna and the Steppir doesn't always go to the same resonant frequency as
I change bands and modes within those bands. However, that automatic plate circuit tuning goes nuts when I try to push the power to 1500 Watts.? Automatic tuning doesn't like to go above 1100 to 1200 watts (depends on the band) and stay still.
Any thoughts?? I do have a supposed NOS 8877 in the original Eimac box.? I just want to know if this is what to expect from an aging Thompson 8877 or any aging 8877.
73,
Dave, w6de
|
Re: Symptom(s) for a fading 8877 tube?
Hi Dave.
My question is about your AC mains supply. Is it up to the task?
Section 3.2 and table 3-1 talk about what you can expect from
different mains supplies.
Also, I looked in the manual to see if they mentioned the anode
voltage but found no mention of it. Is 3200V the correct voltage
and what does it sag to on key down? Excessive sag will also
affect your heater voltage.
The Eimac datasheet says 1085W out at 2700V anode voltage.
Look at all the above before you go changing the tube.
73 and good luck, Alek VK6APK.
On 15/10/2023 7:21 am, Dave w6de wrote:
toggle quoted message
Show quoted text
Good point, if the cathode emission is
down, there aren’t enough electrons being ejected from the
cathode to make the higher power levels.? Time to switch
tubes.? Since this amplifier case is already full and I have a
spare tube, ?I’m not going to hack it up to make the filament
voltage adjustable.?
But I going to wait until after the bands
quiet down. ?Right now, I don’t want to side-line the Alpha
9500 for my first time (with this amplifier) tube replacement
and de-gassing cook in.
?
73,
Dave, w6de
?
?
?
If the tube is half in the grave, Increasing Filament voltage
and current to increase emission from the remaining cathode
carbon may help until the end ?
?
73
?
vk4tux
On 14/10/23 14:21, Dave w6de wrote:
I have an Alpha 9500 and I find it
difficult to get 1500 Watts out of the current Thompson
8877--age unknown.
The symptom is: I can easily get 1,000 to 1,100 Watts out of
the amplifier but continuing to increase the drive level (to
get power above 1.3KW) power output does not continue its
somewhat linear increase in power output.?
I reach a level where I am concerned about increasing the
drive because I don't see increase in output power.? And the
grid current is reaching 90 Milliamps where I stop trying.
There is 3,200 Volts on the Plate and the plate current
won't increase above ≈ 0.7 amps without exceeding grid
current limits. Running class AB2 a linear is about 60%
efficiency I should be getting about 1,344 Watts and I'm
seeing 1370 Watts on the built-in power meter which matches
my Bird power meter pretty closely.? But When I try to
increase the drive, the amplifier will momentarily indicate
1500 watts but immediately drop back to 1300 watts.
All testing into a large surplus 50 Ohm dummy load.
Side Note: the Alpha 9500 has automatic tuning of the
plate/output circuit.? I leave it on as I do several band
and mode changes during an operating session.? And I and use
a Steppir antenna and the Steppir doesn't always go to the
same resonant frequency as I change bands and modes within
those bands. However, that automatic plate circuit tuning
goes nuts when I try to push the power to 1500 Watts.?
Automatic tuning doesn't like to go above 1100 to 1200 watts
(depends on the band) and stay still.
Any thoughts?? I do have a supposed NOS 8877 in the original
Eimac box.? I just want to know if this is what to expect
from an aging Thompson 8877 or any aging 8877.
73,
Dave, w6de
|
Re: Symptom(s) for a fading 8877 tube?
I’ll do that this afternoon.
?
73,
Dave, w6de
?
toggle quoted message
Show quoted text
From: [email protected] < [email protected]>
On Behalf Of Alan - W5ARM via groups.io
Sent: 15 October, 2023 02:04
To: [email protected]
Subject: Re: [ham-amplifiers] Symptom(s) for a fading 8877 tube?
?
No need to "side-line" your amp... just throw that spare 8877 in and run it!
Also, being that the 8877 (3CX1500A7) is a ceramic tube, there's no need to "cook" it in or do any sort of "degassing", or anything else.? They are not prone to leakage, as a lot of old glass tubes are (like the 3-500Z's).
Tube swap is very easy, only takes about 30 minutes...? Removing (and reinstalling) all of the cover screws takes longer than the actual tube replacement. LOL!? Pull that old one out, plug the new one in, hook up the anode lead, put on the cover... and you're
set.
I swap the tube in my big Henry 3K-Classic fairly often (I go between an 8877 and a 3CPX1500A7, pulse rated tube).? In addition, I just recently swapped-in a spare Eimac YU-157 into my Alpha 9500 (pulled the OEM 8877 out) just to exercise it.? I'll run it for
a while, then pull it out and go back to the 8877.? No problems whatsoever.
As long as your no-drive idling plate current is good (which it should be, if your spare tube is good), you shouldn't need to do anything else.
73,
~Alan
W5ARM
|
Re: Symptom(s) for a fading 8877 tube?
I may just do that after I test my spare tube.
73,
Dave, w6de
toggle quoted message
Show quoted text
-----Original Message----- From: [email protected] < [email protected]> On Behalf Of Scott, KB3JQQ via groups.io Sent: 15 October, 2023 03:04 To: [email protected]Subject: Re: [ham-amplifiers] Symptom(s) for a fading 8877 tube? Plan B: The few extra hundred watts really doesn't make much difference. Just use that tube until it doesn't...... On 2023-10-14 22:04, Alan - W5ARM wrote: No need to "side-line" your amp... just throw that spare 8877 in and
run it!
|
Re: Symptom(s) for a fading 8877 tube?
Plan B: The few extra hundred watts really doesn't make much difference.
Just use that tube until it doesn't......
toggle quoted message
Show quoted text
On 2023-10-14 22:04, Alan - W5ARM wrote: No need to "side-line" your amp... just throw that spare 8877 in and run it!
|
Re: Symptom(s) for a fading 8877 tube?
No need to "side-line" your amp... just throw that spare 8877 in and run it!
Also, being that the 8877 (3CX1500A7) is a ceramic tube, there's no need to "cook" it in or do any sort of "degassing", or anything else.? They are not prone to leakage, as a lot of old glass tubes are (like the 3-500Z's).
Tube swap is very easy, only takes about 30 minutes...? Removing (and reinstalling) all of the cover screws takes longer than the actual tube replacement. LOL!? Pull that old one out, plug the new one in, hook up the anode lead, put on the cover... and you're set.
I swap the tube in my big Henry 3K-Classic fairly often (I go between an 8877 and a 3CPX1500A7, pulse rated tube).? In addition, I just recently swapped-in a spare Eimac YU-158 (a newer version of the 3CPX tube) into my Alpha 9500 (pulled the OEM 8877 out) just to exercise it.? I'll run it for a while, then pull it out and go back to the 8877.? No problems whatsoever.? The Eimac YU-158 tubes, as well as the Eimac 3CPX tubes, come up for sale on eBay fairly often...
As long as your no-drive, idling plate current is good (which it should be, if your spare tube is good), you shouldn't need to do anything else.
73,
~Alan
W5ARM
|
Re: Symptom(s) for a fading 8877 tube?
Good point, if the cathode emission is down, there aren’t enough electrons being ejected from the cathode to make the higher power levels.? Time to switch tubes.? Since this amplifier case is already full and I have a spare tube, ?I’m not
going to hack it up to make the filament voltage adjustable.?
But I going to wait until after the bands quiet down. ?Right now, I don’t want to side-line the Alpha 9500 for my first time (with this amplifier) tube replacement and de-gassing cook in.
?
73,
Dave, w6de
?
?
toggle quoted message
Show quoted text
From: [email protected] < [email protected]>
On Behalf Of Adrian Fewster via groups.io
Sent: 14 October, 2023 04:36
To: [email protected]
Subject: Re: [ham-amplifiers] Symptom(s) for a fading 8877 tube?
?
If the tube is half in the grave, Increasing Filament voltage and current to increase emission from the remaining cathode carbon may help until the end ?
?
73
?
vk4tux
On 14/10/23 14:21, Dave w6de wrote:
I have an Alpha 9500 and I find it difficult to get 1500 Watts out of the current Thompson 8877--age unknown.
The symptom is: I can easily get 1,000 to 1,100 Watts out of the amplifier but continuing to increase the drive level (to get power above 1.3KW) power output does not continue its somewhat linear increase in power output.?
I reach a level where I am concerned about increasing the drive because I don't see increase in output power.? And the grid current is reaching 90 Milliamps where I stop trying.
There is 3,200 Volts on the Plate and the plate current won't increase above ≈ 0.7 amps without exceeding grid current limits. Running class AB2 a linear is about 60% efficiency I should be getting about 1,344 Watts and I'm seeing 1370 Watts on the built-in
power meter which matches my Bird power meter pretty closely.? But When I try to increase the drive, the amplifier will momentarily indicate 1500 watts but immediately drop back to 1300 watts.
All testing into a large surplus 50 Ohm dummy load.
Side Note: the Alpha 9500 has automatic tuning of the plate/output circuit.? I leave it on as I do several band and mode changes during an operating session.? And I and use a Steppir antenna and the Steppir doesn't always go to the same resonant frequency as
I change bands and modes within those bands. However, that automatic plate circuit tuning goes nuts when I try to push the power to 1500 Watts.? Automatic tuning doesn't like to go above 1100 to 1200 watts (depends on the band) and stay still.
Any thoughts?? I do have a supposed NOS 8877 in the original Eimac box.? I just want to know if this is what to expect from an aging Thompson 8877 or any aging 8877.
73,
Dave, w6de
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Symptom(s) for a fading 8877 tube?
I have an Alpha 9500 and I find it difficult to get 1500 Watts out of the current Thompson 8877--age unknown.
The symptom is: I can easily get 1,000 to 1,100 Watts out of the amplifier but continuing to increase the drive level (to get power above 1.3KW) power output does not continue its somewhat linear increase in power output.?
I reach a level where I am concerned about increasing the drive because I don't see increase in output power.? And the grid current is reaching 90 Milliamps where I stop trying.
There is 3,200 Volts on the Plate and the plate current won't increase above ≈ 0.7 amps without exceeding grid current limits. Running class AB2 a linear is about 60% efficiency I should be getting about 1,344 Watts and I'm seeing 1370 Watts on the built-in power meter which matches my Bird power meter pretty closely.? But When I try to increase the drive, the amplifier will momentarily indicate 1500 watts but immediately drop back to 1300 watts.
All testing into a large surplus 50 Ohm dummy load.
Side Note: the Alpha 9500 has automatic tuning of the plate/output circuit.? I leave it on as I do several band and mode changes during an operating session.? And I and use a Steppir antenna and the Steppir doesn't always go to the same resonant frequency as I change bands and modes within those bands. However, that automatic plate circuit tuning goes nuts when I try to push the power to 1500 Watts.? Automatic tuning doesn't like to go above 1100 to 1200 watts (depends on the band) and stay still.
Any thoughts?? I do have a supposed NOS 8877 in the original Eimac box.? I just want to know if this is what to expect from an aging Thompson 8877 or any aging 8877.
73,
Dave, w6de
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These tubes have been sold. I am sorry I could not provide them to all who asked, but the first respondent got all three. Thanks & 73 – Mike ? Mike B. Feher, N4FS 89 Arnold Blvd. Howell NJ 07731 848-245-9115 ?
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From: [email protected] < [email protected]> On Behalf Of Mike Feher Sent: Wednesday, October 4, 2023 7:59 PM To: [email protected]Subject: [ham-amplifiers] 3CPX1500A7 tubes FS ? So, the tubes I have are actually 3CPX1500A7 tubes. These are the pulse rated 8877 tubes. I would like $1800 for all three. They are in their original foam filled boxes. Photos attached. Thanks & 73 – Mike ? Mike B. Feher, N4FS 89 Arnold Blvd. Howell NJ 07731 848-245-9115 ?
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Re: Stiff tuning capacitor
But it seems to work well!
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Re: Stiff tuning capacitor
Where I used to work we referred to Kroil as ‘weasel piss’ and ‘millwright’s aftershave’! ? Mod-U-Lator, Mike(y)/W3SLK ? ? ?
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From: [email protected] [mailto:[email protected]] On Behalf Of Richard P via groups.io
Sent: Thursday, October 12, 2023 4:50 PM
To: [email protected]
Subject: Re: [ham-amplifiers] Stiff tuning capacitor ? Well, I pulled out one of my blunt-needle syringes that I use for applying really small amounts of stuff, and hit both bearings of the air variable with a drop of Kroil, “The oil that creeps.” Love that stuff, but not cheap. Anyway, the cap is turning freely now. But I’m pretty sure this is a temporary fix. Time will tell. Prob need real lubricant in there.?
Richard
WB5NEN
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HaL Mandel
Alan - W5ARM
Scott, KB3JQQ