[Amps] Question for the tetrode experts

[Carl]

> Thanks to everyone for your responses. Here are the answers to all of the 
> questions, plus latest results.
>
> The band is 40 meters. There are no padder capacitors in the circuit on 
> this band. There was a ferrite 'safety' choke across the output. It was 
> getting warm, so I replaced it will the usual 3 mH (300 mA?) pie-wound 
> type. I will revisit this because I want a choke that will blow the PS 
> breaker if the blocking cap shorts and I don't know if this one will.
>
> I think this choke was part of the problem.
>
> To answer G3RZP, the plate choke is an Ameritron 225 uh choke. The bypass 
> is an 0.01 disc in parallel with an 0.001 at the bottom of the choke. Then 
> there is a 25 ohm 50w glitch resistor, which is bypassed at the cold end 
> by a second 0.01. The HV coax is also bypassed by a third 0.01 where it 
> exits the RF deck.
>
> The plate, screen and bias voltages are solid. What I am seeing now is 
> that the screen current drops while I hold the key down for 10 seconds, 
> from around 25 to 13 mA. But it more or less stays there and the amp 
> doesn't fault.
>
> Tuning is VERY touchy. You really have to have the loading right or the 
> screen current is excessive in either direction.


Consider using less variable Load C on the higher bands plus a vernier as 
most commercial amps use.

Carl
KM1H