Drake L7 Linear Amplifier is a little weird part 1 output circuit

[@mikesradiorepair]

The capacitor is used to prevent self resonance of the plate choke. Why did they use that type capacitor? If I had to guess, cost. Without the capacitor the choke will self resonate around the 15 Meter and 10 Meter bands.

[@tramdr]

That was my theory, except my guess would be that its the 160 meter band that is self resonant.

[@bblod4896]

Cool. Special made capacitor, plate on each side with an insulator in the middle. If you measure the thickness of the insulator and measure the plates, you could have them made by PCB Way or another PC board manufacturer.

[@tramdr]

I'll just go with doorknobs. Henry Radio also used plates like this in some of their amps. One was a variable and they moved the whole plate in and out to adjust the capacitance.

[@dieseldes6578]

At a guess, the choke must resonate at certain frequencies, and so that odd looking capacitor is to try and tune it out of resonance? A VNA and a frequency sweep might help and answer the question, eg where does it resonate with and without the cap in circuit. Does the amp run on 12, 17 and 30 meters? If not someone maybe forced it on there and the choke resonated and cooked the cap? GI0UTE, 73

[@tramdr]

The amp does not have 12-17 and 30, only has 10-20-40-80 and 160. The weird cap is factory. I'm thinking its there for 160.

[@MM0IMC]

I'm guessing that's it's to remove unwanted resonance on the plate choke, which could overheat and destroy the choke, at certain frequencies. 🤔 The coil before the tune cap might be part of a PI L tank circuit? 🤔 Another guess, unfortunately.

[@tramdr]

I am pretty familiar with Pi L's but I have never seen that on the Tune side of the tank. It's always after the Load cap.

[@thesquirrelchroniclesakare7808]

Are these for sale Doc ?

[@tramdr]

I will probably sell one of the 2 L7's I have but it won't be cheap.

[@Rooster_Radio]

burning the midnight oil

[@tramdr]

lol.

[@N3WERHamRadioElmer]

Rabbit 102 & The "Fat Man on The Hill" in the Keystone Watched your Video & We Got Down.. 73's

[@tramdr]

Thanks for the support.

[@1112223333111]

thats gotta be some 11m filter bs. I'd take the l4b over these for sure.

[@tramdr]

but these are prettier