The pair of 4CX250s can't draw more than about 600mA peak plate current,
with a much lower average than that. 25uF should be sufficient. My
homebrew 2 x 4CX250 amps for 2m and 135cm have 28uF/2500V filter in their
common power supply and I can't see or hear any ripple on the CW signal when
running 800W key-down output power. The dynamic regulation is a function of
many factors, and mine is pretty good: About 2500V key-up and 2200V key-down
at 600mAdc (closed key for several seconds).
Note the 2500V is a bit more than the tube's actually rated for, but I've
used this voltage for almost 25 years and my 2m amp's still got the same
pair of tubes in it, working the same as they did when new in 1980.
WB2WIK/6
"There is no reason anyone would want a computer in their home." - Ken
Olson, Chairman & Founder, Digital Equipment Corporation (1977)
> -----Original Message-----
> From: Angel Vilaseca [SMTP:avilaseca@bluewin.ch]
> Sent: Monday, August 16, 2004 9:13 AM
> To: amps@contesting.com
> Subject: [BULK] - [Amps] Filtering capacitor in a HV PS: How low can
> you get away with?
>
> Hi,
>
> I am building a 2500 V power supply for a one-KW transmitter. It will
> use 2 4CX20Bs.
>
> I have two oil-filled capacitors: 2.5 KV 40 uF and a 4 KV 25 uF.
>
> I feel quite uncomfortable using the 40 uF 2.5 Kv one, because it would
> work very close to its voltage limit.
>
> On the other hand, the 4 KV 25 uF would be OK as far as voltage is
> concerned, but would not 25 uF be too low?
>
> Is there a rule of thumb ? How low can you get away with capacitance in
> a HV power supply feeding two tetrodes?
>
> Vy 73
>
> Angel Vilaseca HB9SLV
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