Re: Tube radios as RF amplifier

Bill Cromwell

Hi Robert,

In the 80s I had an Argonaut 509 rated to produce 2 watts of RF (CW/SSB). Sometimes QRP (less than 5 watts) is inadequate. I acquired the remains of a Heathkit DX 35 and turned the final amp into boots for my 509. I had to build a power supply since the original was not present. You could also modify the original if you have it. I biased the 6146 tube I used for class AB1 so that no grid current ever flows. I added a solid state electronic T-R switch as presented in QST or the ARRL Handbook. The 509 has a separate antenna input available for the RX section and I used that. You may have to use a T-R switch and relay to accomplish the T-R function. If your qrp rig is separates that problem is eased quite a bit.

I estimate the drive power delivered by the 509 was in the low milliwatts. Some publications of tube parameters suggest a 6146 with AB1 bias would be 100 to 200 mW. I forced the input to ~50 ohms with a swamping resistor. Watch out that you don't overdrive the tube.

My boots took me from sometimes being able to checkin to NTS traffic nets on 80 meters to reliable NCS operation and full QSK. It's worthwhile. Good luck with your project.


Bill KU8H

On 05/15/2017 05:04 AM, Robert Rode [4sqrp] wrote:
Morning all, I wonder what wud be required to drive grid of old Heathkit as amplifier with qrp rig... DE W9ESX Chicago...
bark less - wag more

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