[Diabolical Artificer]

Still fettling this amp, am now working on the chassis, PSU and protection circuits.

I'm going to use a NOS ceramic dropper R of 67 ohms on the HT to soft start the amp. This will be shunted by a relay after about 8 seconds. It means I can use a smaller fuse on primary too. Smaller fuse, quicker to blow. All mains tfmr secondaries will have fuses as well as a fuse on the HT after the reservoir caps.

I want to knock up protection in case an OP valve starts conducting too much too. Havn't worked out how to do that yet. But as each cathode has a 10r "sense" resistor, maybe I can do somethiing with the voltage across these but to turn on an SCR or something to trip a relay that will cut power to the mains tfmr primary.

For no load on the OPT secs I was going to use a 1k R across the speaker out terminals as well as diodes on each half of the primary of the OPT.

Am sure there was something else, but if anyone has any suggestions....

I've painted myself into a corner regarding the PSU. I've not left much room to fit a 625VA toroid, two bridge rectifiers, 6 big caps, fuse board, two big relays, protection etc PCB etc.

Regarding the fuses I've had an interesting morning trying to find a lot of capacitance in as small a size as possible, at high voltage for as little as poss £'s. I did have 8 220u 385v and two 150u caps in series parallel, but miscalculated capacitance. I've calculated I'll need around 1000u with HT around 500v at times that means a 1000u 550v cap. Not cheap, your talking around £50 each!

The cheapest way I found was to use four 820u 315v and two 470u 315v caps. so thats two 820u and a 470u in parallel across one 230v secondary, with the same again. I'm pretty sure this comes to 1235u at 630v. Series parallel circuits always fox me a little.

I'll have some pics soon.

Andy.