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
?
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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:
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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
?
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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
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Re: Symptom(s) for a fading 8877 tube?
I may just do that after I test my spare tube.
73,
Dave, w6de
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-----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!
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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......
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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!
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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
?
?
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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
|
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
|
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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Re: 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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Re: Stiff tuning capacitor
Hi Don,
?
That’s exactly what Lt.Cmdr (Ret.) MSRN Atilla the Hun
advises me from time-to-time.
?
Hal
?
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Re: High filament current on the 8877 amplifier tube
Hi Tim,
?
What a great idea for proofing performance on 8877’s.
?
These things are carbonized in production with
burning acetylene gas. I’m sure there is a
controlled process combined with high vacuum
that sets the amount of carbon deposition, but what if
different amounts or densities of carbon settled in
the envelopes, making for a variance in filament
amperage?
?
Hal
W4HBM
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Re: Stiff tuning capacitor
3-in-One oil ... one drop.
W4DNR
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On 2023-10-12 7:42 am, Richard P via groups.io wrote:
Mine used to turn freely throughout its range, but now, it’s gotten kind of stuff. Annoying. Maybe a shot of penetrating oil on the “bearings,” or what??
Richard
WB5NEN
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Re: Stiff tuning capacitor
Be careful with WD40. It's flammable. I've had good luck with 0w-20 FULL SYNTHETIC engine oil. It also works well for clocks, guns, etc. Bob W4JFA?
On Thu, Oct 12, 2023, 10:44 AM HaL Mandel < hmandel@...> wrote:
Zoro.com sells tiny tubes of it….
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Re: High filament current on the 8877 amplifier tube
When I built my 8877 tube tester – I metered everything (four meters). It is amazing to see what happens with a cold 8877 and bringing up the filament voltage via a variac slowly to 5 VAC. A cold filament wants to draw lots of current. Bringing them up slowly is the key. That is why I have step starts on ?the filament voltage on my homebrew 8877 single band amps… ? So we (DL1QQ is helping) are testing the spare “fleet” of 8877s here (yearly event) at K3LR and so far twelve 8877 spares all draw 11 amps of filament current (after warm up). That is o Eimac spec. Four other 8877s draw 15 amps (HV has not been applied to these yet). I have 18 contest amplifiers here – they all use the 8877. So spares are very important. ? The 8877 tube HV tests vary from 300 mA to 410 mA at 2900 volts (also on a variac). The more current – the healthier (more output) the tube has. ? 73 Tim K3LR ?
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From: [email protected] [mailto:[email protected]] On Behalf Of Jim VE7RF
Sent: Thursday, October 12, 2023 10:27 AM
To: [email protected]
Subject: Re: [ham-amplifiers] High filament current on the 8877 amplifier tube ? I would also measure the C? between? anode to grid....and also grid to cathode, and also anode to cathode..... and also cathode to heater.? Still baffles me why a tube would draw 36% more current.? ? Then again, how many owners of 8877? amplifiers? measure fil current, probably none.? I? measure? fil current on all my hb triode amps, with directly heated cathodes....with a front panel, panel meter.? Just a 0-75 amp meter, with the mating 75:5 xfmr...that loops around one of the fil leads... on? my 3x3 amp.? The 3x6 amp gets a 0-100 amp meter, with the mating 100:5 xfmr.? ?'Step start' in both cases consist of bringing up the small variac real slowly till desired voltage is obtained...(on a separate fil V meter).??
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Re: Stiff tuning capacitor
Zoro.com sells tiny tubes of it….
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Re: High filament current on the 8877 amplifier tube
I would also measure the C? between? anode to grid....and also grid to cathode, and also anode to cathode..... and also cathode to heater.?
Still baffles me why a tube would draw 36% more current.? ? Then again, how many owners of 8877? amplifiers? measure fil current, probably none.?
I? measure? fil current on all my hb triode amps, with directly heated cathodes....with a front panel, panel meter.? Just a 0-75 amp meter, with the mating 75:5 xfmr...that loops around one of the fil leads... on? my 3x3 amp.?
The 3x6 amp gets a 0-100 amp meter, with the mating 100:5 xfmr.? ?'Step start' in both cases consist of bringing up the small variac real slowly till desired voltage is obtained...(on a separate fil V meter).??
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Re: Stiff tuning capacitor
Thank you. Yes, air variable. I do not have the moly di grease, but my neighbor has everything. I’ll check with him to see if I can get a dollop.?
R
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Scott, KB3JQQ
Alan - W5ARM
HaL Mandel
Bob