G4DCV GS31b 144MHz Amplifier/gs31-7.jpg

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

The HT voltage will kill

Mounted on the back panel are two Amphenol coax relays to allow the amplifier to be bypassed. The top of the new, bigger, heat-sink for the TIP47 bias transistor is just visible below them.

The bias circuit and metering is as used by GM3SEK in his Triode Board, page 30, but using the higher bias modification in Appendix 1 page 39. I built it on a home-made PCB. Since re-reading the Triode Board manual I have realised that when using a GS31b this circuit needs a much bigger heatsink than the one in the picture so I have replaced it. GM3SEK says, "4in x 3in x 1in, or equivalent (2°C/W or less). For low bias voltages and lower-power tubes, you can mount Q1 on a cool area of the chassis". My italics.