Gidday all..I have been keeping busy these past few weeks...I delivered a new GS-31B 2 meter amplifier to a friend a month ago and he asked me if I would build a 6 meter twin..I got to work a couple of weeks ago and put this one together...Pretty straight forward with no bells and whistles, just the old homebrew Heathkit style..
The amplifier has soft start for HT, adjustable tube bias from the front panel and other normal controls..The HT transformer delivers 1300vac @ 1.5 amps CCS...It is voltage doubled and gives around 3500vdc...Minor supply's are 24vdc for relays and 20vdc for the cooling fan...I used a Papst 5 inch 12-28 volt fan for cooling...This fan produces around 225cfm in free air and is more than adequate to cool the GS-31B tube...The RF deck is pressurised and the air goes through the tube cooler and exits through a Teflon chimney on the top cover..
The amplifier uses a simple Tuned T input network on the cathode and a Pi-L network on the Business End..I built the case so that there is plenty of room under the hood for maintenance and easy servicing...The front panel hinges down to expose the main control wiring etc...All wiring is color coded for the various amplifier circuits and functions...
I set this amplifier up on the test bench last Monday morning and gave it a run...The amplifier tuned up perfectly first try and I only had to tweak the T input network variable capacitor..Bypass vswr is 1-1...Drive vswr is 1.2-1...I ran the amplifier up to 1kw output with around 45 watts drive, didn't bother driving it any harder....The owner only wants a reliable 500 watts in all modes....This amplifier does the deal..
Delivered the amp this morning and one really happy owner...I like it when things go well..
A few pics....Enjoy..Bob..VK3ZL..
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Originally Posted by KG4CGC
