Drake L-7 Linear parts
 

I have a Drake L-7 linear that has blown the "printed circuit board"
capacitor C-41 that is across part of the RF choke RFC 4. This choke
sees the total amps drawn by the linear as it is in series with the HV
input from the P/S and feeds the two 3-500 tubes. However, I don't
know what voltage rating a commercial part would be for a replacement,
and if it could be obtained. Someone has recommended at least a 5KV
rating.

Anyone have any ideas on a replacement??? Also maybe I could make one
from some double sided glass PC board I have here. The cap in the
linear is 1 inch by 3 inches in size. There is also another one of the
same type, but much larger hanging off the "load" variable capacitor.
It seems to be in good condition.

I have found nothing else in the linear that looks bad or measures bad.

So it looks like the C41 cap failed and took out the 0.82 ohm resistor
in the P/S HV lead. At least I hope that is all that is wrong.
Appreciate any thoughts anyone might have on this subject.

Harold, N3HP

Harold,

You have a problem somewhere else. The capacitor failing cannot take out the
0.82 ohm resistor. Whether that capacitor is in the circuit, shorted, or open,
it has no effect on the current drawn from the linear, thus that resistor is
unaffected. It is possible, however, that you had a parasitic oscillation, or
perhaps something shorted the capacitor to ground (dust, spider webs, or who
knows what). There is not a lot of dc voltage across that capacitor. If there
were, the section of the RF choke in parallel with it would fuse open. RF
voltage is another issue. At any rate, I would guess a 5 kv unit would work.
Drake made a retrofit kit that replaces that printed circuit capacitor with a
fixed value doorknob. Bill Frost at Drake can give you the specifics. The L-7
is basically a good amp.

73s,

Evan

Harold,

You have a problem somewhere else. The capacitor failing cannot take out the
0.82 ohm resistor. Whether that capacitor is in the circuit, shorted, or open,
it has no effect on the current drawn from the linear, thus that resistor is
unaffected. It is possible, however, that you had a parasitic oscillation, or
perhaps something shorted the capacitor to ground (dust, spider webs, or who
knows what). There is not a lot of dc voltage across that capacitor. If there
were, the section of the RF choke in parallel with it would fuse open. RF
voltage is another issue. At any rate, I would guess a 5 kv unit would work.
Drake made a retrofit kit that replaces that printed circuit capacitor with a
fixed value doorknob. Bill Frost at Drake can give you the specifics. The L-7
is basically a good amp.

73s,

Evan