Homebrew 2 Meter GI46B
Amplifier using the YU1AW design

 

I decided to build a ssb amplifier for 144.200 ssb usage and because I had a transformer that was rated for 330ma I decided to use the GI46B.

My main reasons were 1) lower drive required (20-40 watts) and 2) lower current draw (300-400ma)

As it turned out, the transformer produced 3100VDC using a bridge rectifier, and most schematics said that only 2000VDC was required for 500 watts out.

I did some research and the tube would be able to handle 5kv or more in pulse mode, so I figured I'd give it a whirl.

I had to burn in the tube for several days with only filament voltage,

then I used a variac to set up the plate voltage over several hours to make sure that the tube wouldn't complain.

I was pleasantly surprised when I connected the wattmeter  and saw just under 800 watts out with 40 or so watts drive!!!!

I converted the left meter to an RF output meter, who cares what the voltage is :)

This amp can be yours for $950 picked up at my location. We can discuss shipping.

Cabinets are $150 shipped
NEW old stock GI46B tubes $100 shipped
Plate transformer $250 shipped

I don't always have these in stock, there may be some delay in sending them to you, depending on where they come from..

Here is the plate circuit (Lazy builders design)

 

120vac 105CFM fan

In the photo below you can see the PTFE chimney.

Power supply with the original transformer
(replaced with a MUCH larger one shown below)
Note the 12.6VAC filament transformer, 12VDC supply for the relays and the timer for 2 minute delay on the HV transformer relay.
This allows the filament to heat the tube before the HV comes on. I also prevents keying of the amplifier as well.

tuned input, filament choke, bias board etc.

antenna switching.

 

The new transformer. rated at 800ma giving me 2800 VDC!

HV Rectifiers and 8ea 450V caps. 2800VDC 800ma

I used a modified version of this schematic.
1) I used a W4ZT bias board.
2) I used a different tuned input
( 2ea 4 turn 5/8" ID coils with a 50pf variable cap),
3) I used a 1000pf cap for Ca instead of the PCB, and
4) I have 2800VDC on the plate.

 

With 7 watts drive, I get 300 watts output.

With 25 watts drive, I see 650W out.

40 in gives me about 800.
(my current rig (TR-751a) is a 25w rig)

Contact me about this amp.

W4VAS
2/22/2016

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