[mike s]

The Vortexion guitar amplifier is now working pretty well. I replaced the four CL33 with EL33 and the metal rectifier and dropper with a transformer and silicon diodes. All that's need now is a safe mains switch and power connector and it's done. I'll lend it out to a friend with guitar to see what he thinks of it.

So now I need to pick my next project. I have another AC/DC amp. One of these -
http://www.vintagehofner.co.uk/selmer/early/pa.html though I don't have the speakers. I'm thinking that this time I'll keep the series heater arrangement but use an isolating transformer. It looks like I can take the heaters from a 120V tap on a 240V transformer to avoid having a dropper resistor. Which seems like a tidy solution.

But before I do that I'm tempted to fix an RCA 82 C4 Monitor Amplifier. It's like a BA-4C has the same transformers, but uses two 6J7 triode strapped rather than 6SN7. I guess it must have been made just before production of BA-4C started. I see hardly any RCA amps in the UK, but I guess they're pretty common in the US. Unfortunately half the primary of the output transformer is open circuit so I'll either have to fix it - unlikely to be possible, certainly not easy as it's potted - or replace it. I have an old Partridge transformer from a GEC KT66 push pull amp, also with a tertiary winding, that might be suitable.

I'm certainly more interested in hearing what the RCA sounds like. Which project would others choose?