John,
Same output capacitance in grounded grid configuration. My BIBLE only shows
the feedthrough capacitance as varying from .1pF to .2pF for the 3CPX.
PLUG THEM IN.
Its been already mentioned from the experienced faces here that we've been
using them for 20 plus years interchangeably.
Where there is a nice voltage improvement in the 3CPX800 version for ham
use, there isn't a big benefit in the 1500 watt version as the two major
limiters to power as I stated before are ANODE DISSIPATION and the 1 AMP
Cathode Current.
The 8877 already had been tested by Eimac to 8KV before they built the 3CPX.
However I don't recommend running them over 5KV standby plate voltage.
This isn't a tested limit in practical use, it is a practical limit as
applied to tested use. They behave well at 5KV and under in HF use. They
put out power nicely at 5KV and under, you always stand an increased chance
of tube arc destroying your tubes at a voltage above the point they arc,
HAHAHAHA.
I have not tested an 8877 at VHF or higher with more than 4200V resting.
(However I have run a 3CPX at nearly 5kV in a Henry 4K-Ultra 50 MHz.) I
usually am more conservative with voltages above 30 MHz.
BOB DD
-----Original Message-----
From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com] On
Behalf Of John T. M. Lyles
Sent: Monday, January 22, 2007 10:58 AM
To: amps@contesting.com
Subject: [Amps] 3CX1500A7 versus 3CPX1500 TSPA
With all the hoopala here questioning honesty of selling various
8877-style triodes as interchangable, I didn't see mention of whether
the pulsed tube (having a longer anode ceramic) would have the same
Cpg, output capacitance. This may make a big difference in a
particular amplifier, esp at the higher frequencies. Beside the
obvious of it sticking up higher in the socket, the tuning may get
offset by the fixed tube capacitance, something to be aware of. Moot
point, since it was sold already, but be careful of interchangeable
sockets without heeding noninterchangeable tube characteristics.
73
John
K5PRO
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