New home-brew 40 meter RF deck

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W8ACR:
I'm back. It's been a few years since I have posted anything in the technical forum, but I'm still loving AM, and I just finished a new home-brew 40 meter RF deck that I wanted to show off. This is a classic push pull triode design, 1940's technology. I'd appreciate any feedback/critique on my design or workmanship. The tubes are HK-54's (thank you Dennis Gilliam) and will be operated at about 1600V@250mA. I just finished it tonight, so I haven't tuned it up yet or had it on the air. That will be tomorrow, and I will let you know how it goes.

The grid circuit is conventional. The grid capacitor rotor is grounded for DC. There are home-brew parasitic suppressors in the grid leads. Both the grid and the plate leads are connected to the tube pins by Fahnstock clips.

The plate circuit is also conventional. The plate coil is home-brew with a fixed link. I didn't have a TVL 40 coil, so I had to roll my own. The primary winding is #12 THHN wire on a PVC coupling. The fixed secondary winding is vintage cloth covered #12 stranded hookup wire, and has 4 turns. I designed the plate circuit for a Q of somewhere between 6 and 10. The plate leads are silver plated copper strap. The plate capacitor rotor is grounded for RF, and is connected to the B+ line through a 27K, 1 watt carbon resistor.

Both plate and grid tuning knobs are on verniers and tune very smoothly. There is metering for plate voltage, plate current, grid voltage, grid current, and filament voltage. Meters are located on a separate deck.

I have some critique of my own work.

1. The neutralization caps do not match. This detracts from the cosmetic appearance, but should not affect the function.

2. The grid tuning capacitor is a bit small. Since I should only need about 30 watts of driving power, I think I will be OK.

3.The grid circuit is not physically symmetric. Since it is underneath the chassis, again, I think I will be OK

Pics are below. I'll get back with more info after I tune it up.

W8ACR:
More photos

N1BCG:
Nice craftsmanship! It's good to see projects like this in 2018, particularly those that employ classic or unique components. Hope to hear it on the air!

W8ACR:
LOL, I was just looking at the pictures again. I think I'd better connect the grid capacitor to the grid coil. :-[

Ron W8ACR

WD5JKO:

  Ron,

   Wow Ron, that could have been in a late 30'd radio handbook! Nice construction. Yes hook up that grid tuning cap! :-)

   You might find the fixed link on the output tank overly restrictive. A swinging link with a jack bar setup allows for loading to the same plate current for varying load impedances. Years ago I made a P-P AM kilowatt setup, and I had the swinging link along with a series adjustable C (large capacitance) to tune out the link reactance. The flexibility was really useful.

Jim
Wd5JKO

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