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 ¡Ö 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
