[Amps] 3CX1500A7 versus 3CPX1500 TSPA

[John T. M. Lyles]

Hi Bob
thanks for the explanation on the interelectrode capacity. Sounds close.
I have a 3CX1500A7 running around 5 MHz here at work, in a rebuild 
plasma amplifier, to test components. It runs out of plate current 
usually when I push it as the Ep is lower.

Of course, tested at Eimac at 8kV is relative to what atmosphere they 
used. If done in ambient conditions in their factory in San Carlos 
(now Palo Alto), that is near sea level. Mine runs at 7000 feet above 
sea so I have to derate things accordingly or they arc.

Yes, running at VHF with tubes is a bit more problematic as the 
charging current in the leads can be higher and cause losses and 
heating at the seals of the tube. Dielectric heating may also come 
into play for glass tubes, not so much with Alumina ceramic though.

It is usually better to load them heavy with lower Ep when pushing 
the frequency extreme.

73
John
K5PRO


>
>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.