Re: Using Vacuum Tube heathkit as Linear Amplifier for QRP

Gordon Gibby

Thanks very much for sharing that schematic!   Even with the resistive loading it looked like the grid given PA of heathkit transceiver was doing about 16 dB gain.  I wasn’t brave enough to try it higher than 20 m 

Do you have any advice on whether we should try resistive loading higher impedance than 2500 ohms???

By using the tuned plate circuit of the 6cl6 driver, I guess we are already dealing with any grid capacitance in the process

I never did anything like this before (since I home brewed a 3x 811 a amplifier in high school ) it’s pretty cool for me to get back to this

On Nov 10, 2019, at 11:59, ajparent1/KB1GMX <kb1gmx@...> wrote:

The attached image was the solution of the 60 and 70s for hams (and CBers)
for 100W amp. it was cheap 10-13DB of gain.  Alas sweep tubes got expensive 
as people burnt them all up pushing those.  There were generations of them with
up to 6 (SIX!) for a KW input peak.  Not all were clean.

Some did grid driven and they worked save for over drive the grids and the
tubes protest by going away.  At 25$ each that is a bad thing.

For laughs a decade ago I took a 4CX250  and ran it grounded grid like that
and it was good for about 80W (on 6M) out in a simple circuit without forced
air cooling. The tube with screen bias (its a ceramic metal power tetrode)
added did an easy 300w out at 2000V (a very lethal power supply).  The
amp was terminally simple save for a typical tube amp tapped load coil
Pi network for multi-bands.  There are a long list of tubes that can can
be used for that that..


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