[Amps] Cathode Choke

[Roger Parsons]

Many thanks for the comments. My understanding is/was that the PT3000 was a Palstar product, and that the unit I am working on is prototype #5. (And quite possibly I misunderstood/misheard and it was actually Viewstar.) But all the information I have is second hand.

Interesting about the tank circuit arcing on the PT2500 (which I have to assume is from the same product family). The unit I have uses a PI-L tank circuit, with vacuum capacitors at both tune and load positions. There is a large fixed 2n, 10kV paralleled RF rated capacitor used on 160m, and this had destroyed itself. This was definitely in place when the amplfier left the factory, but there clearly had been two parallel 1n doorknob capacitors fitted earlier. No sign of switch arcing, but the 10m position had solder splashes on the contact - also definitely ex factory. The amp has apparently only ever been used on 160m and 20m by the current owner who bought from the factory.

I can't see how that capacitor should fail - it is way over-rated for its position  - except either (1) instability or (2) the output load being absent or removed. I had considered the latter to be much more likely, but can't find anything wrong with either the vacuum relay or the timing/PTT circuitry, so perhaps it is the former.

I have taken a firm decision to remove the choke on the heater - many, many amplifiers work well without it, and it adds what seems to me to be an unecessary layer of complication.

73 Roger
VE3ZI