Well, I ended up changing out the mains transformer. It ended up being the most pragmatic and practical solution to the overvoltage situation.
I also did a load of other work, which included setting myself up with a centre tapped 6V winding on the outside of the toroid, so that the EF80s could get their heater power from somewhere. There is only a 115V + 115V secondary on the toroid. I also found a small 6V/5A transformer, which I fitted inside the black box, alongside the heater transformer feeding the 45s.
This transformer provides the heating for what are now my rectifiers of choice in this amp: a pair of 6CJ3 TV damper diodes. Using them meant fitting a pair of novar sockets in the holes formerly occupied by the octal bases. It also meant that the interior near the blue can cap was clear of the transformer gubbins that had previously been next to it.
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Once everything was powered up, I got some nice readings for the HT and the bias for the 45s. Red meter shows the bias, Blue meter shows the anode voltage:
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These conditions have the 45s operating at 89% anode dissipation.
And here it is playing some nice tunes:
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Thomas Mayer often uses 4 TV diodes in a bridge rectifier setup on most of his amps. My two dampers are configured as a hybrid bridge. I’ve got plenty of them, mostly 6D22S and EY500A, but in this instance I think the top cap less 6CJ3s look a bit more streamlined on this particular chassis, and keep the visual attention on the 45s themselves.
So no more resistors apart from those that are part of the RC filters. It’ll do nicely. The sound is clean, lively, even across the frequency range. The tone is gorgeous and the famous 45 midrange magic is present and correct. I now know and appreciate what the fuss is about concerning these little triodes. Wow!
And even with my 100dB Fane single drivers, the background is silent. Couldn’t ask for much more.
I’m a convert.
Sgt. Baker started talkin’ with a Bullhorn in his hand.