G4DCV GS31B 144MHz Amplifier

If you do not understand high-voltage safety procedures do not attempt to build a tube amplifier.

The HT voltage will kill.



















I am afraid that a schematic diagram does not exist for this amplifier, I built it out of my head in a kind of modular fashion, borrowing parts of circuits that I know work well. Thanks to everyone who publishes their amplifier designs on the web, but particularly to GM3SEK and to YU1AW .

I would suggest anyone building an amplifier use a GM3SEK Triode or Tetrode board. They very much simply amplifier construction. You just need provide a RF deck and power supply. The Triode and Tetrode Boards look after grid bias (and screen supply) and provide comprehensive protection circuits.

I haven't used one in this amplifier although I may retro-fit a Triode Board to this amplifier. I have lifted ideas and circuits from the Triode Board manual which Ian GM3SEK makes available on his web site. In particular I have used Ian's bias and metering circuits and safety principles.

So my amplifier does not have the comprehensive control circuits used in the Triode Board. For example, it does not have an on timer, I use two switches and wait a couple of minutes before enabling the HT and relays. I do use an anti-glitch resistor to protect the tube from flashover. The difference is one of philosophy and what is likely to happen under a fault condition.

I have added a simple grid over-drive protection circuit to this amplifier. See my GI7B amplifier for details.

For example in the case of a flashover the Triode Board will usually shut down the amplifier safely. You push a reset button to be QRV again. In my amplifier the probability is that in the case of a flashover no damage will occur to the amplifier but I would need to power down, unscrew the case and replace the fuses. My method is less convienient, I will be off the air much longer which is not good news particularly in a contest or if there is rare DX about. Importantly opening an amplifier, especially if tired or in a rush to get back on the air (just like happens in a contest), is potentially dangerous. On the other hand the Triode Board costs more than the cheap Russian tube I am protecting. If I was using an expensive Eimac 3CX1500 I'd certainly use a Triode Board. It's a question of design decisions balanced against cost and risks.

If you do not understand high-voltage safety procedures do not attempt to build a tube amplifier. The HT voltage will kill.

I have put comments with some of the pictures. If you have a specific question please email me.

73 Paul G4DCV


Old pictures during construction here