Hi Jim san
The 0.080" gap is equal to 2.0 mm. I think it is not
enough for such a HP amp as your opinion.
It is said that, using a safety factor of 200 % an air
variable capacitor with a gap of 1mm stand 1 kV peak
and 2 mm for 2 kV peak.
Generally the plate potential can be estimated as
DC plate voltage (HV+) plus 1.414 x rt(P x Rp)
Where P is output power [W] and
Rp is plate load impedance [cf. 740 ohms]
the 1.414 represents peak RF voltage.
The DC plate voltage is stopped by a blocking capacitor
so your plate variable capacitor should stand the peak
RF voltage: if P=1500 and Rp=1000 then E=1732V;
if P=3000 and Rp=740 then E = 2107V
So your 3200V DC variable is enough provided the
nominal plate output impedance is low.
But, when a failure of connected load or de-tune of
the pi circuit can put high voltage on the plate VC and
an arc over the gap may happen.
I recommend to use a VC with a gap of 0.14" or 3.6 mm
or, a vacuum variable of 7.5 kV or higher.
de Han JE1BMJ
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|