Somebody might want to get "CURRENT THOUGHTS FROM EIMAC" as just like the
rest of us, attitudes over time.
Like today I hate ham radio, yesterday I didn't, tomorrow I might not again.
When I first got a 3CPX1500A7 in about 1980, I picked up the phone.
Here's what I found out, The higher filament V was a PULSE SERVICE spec.
LIKE 60 AMPS of plate current kinda spec..
The filament current followed suit. BLABBLE BLABBLE, I think I killed all
those brain cells off. That the tube could get plugged right in. I ran one
in a 4K-U at the time.
Anode taller, can handle more voltage, but that was mostly for IMMERSED
SERVICE voltage improvement. RUN it like a regular 8877. Eimac had
actually tested the 8877 to 8KV... Little known secret. 1 or 2 exploded
out of the socket (killing several techs)... so they made the ceramic a
little taller. That's why I don't worry about running up to 5KV on an 8877.
(DO NOT EVER EXCEED 1 AMP or 1500 watts plate dissipation)
Remember transistors have specifications - tubes have guidelines...
Yes an 8938 (3CX1500C7) will do thermal runaway on 432 if you don't lower
the filament to 4.75 under key down. There's nothing scarier. Oh that's
another post.
If you get a good 3CPX it should work good - last long time.
BOB DD
-----Original Message-----
From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com] On
Behalf Of Tom W8JI
Sent: Thursday, January 18, 2007 5:13 AM
To: amps@contesting.com
Subject: Re: [Amps] YC-257 VS 8877
> There is o significant difference worth mentioning. The
> filament voltage of the 3CPX1500A7 is
> specified by Eimac to br 5.5 volts at 11.2 A while the
> 8877 is specified at 5.0 volts at 10.5 A.
> If the amplifier filament transformer only produces 5
> volts, it may reduce the life span of the YC-257 since the
> filament will be 10% lower than specified.
I think you will find the internal structure other than
better insulation is the same as an 8877 and that Eimac only
runs the regular filament/cathode hotter by jacking up the
filament voltage. Other than some very small physical
changes to the envelope the internals are the same. That is
recollection when I was considering running a YC-257. That
being the case emission life should be longer at 5.0 volts
provided peak cathode current is kept within 8877 limits.
Maybe someone can actually contact Eimac instead of
guessing.
73 Tom
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