First of all, Im glad to see some activity here on old Usenet. Most people seem to be in web based forums these days.
In my description of the DC supply, I meant that instead of using the existing 16+16uF cap, I placed two separate caps in the circuit - one 33uF before the choke, and a 47uF after. I did not add another choke or anything.
Phil, thanks for sharing your experiences while I was working on the amps. Since I do not own a dozen of them I could not check what would be the normal behaviour of the circuit.
Patrick, I have read your interesting site about tube electronics. I understand your angle, and I think it is how one should think about new production amps. But in these Quads I was more concerned with safety and longevity than altering the circuit.
I saw a Quad system in a museum recently, together with an early EMT turntable, SPU cartridge, a Revox G36 and so on. Special, quirky but high quality stuff that must to most people seem like steam engines these days. Call me sentimental but I personally dont want to alter such machines too far from how they were made in their time.
I understand the problem with the common cathode resistor, and I wonder if maybe this is one of the reasons many Quads have failed with melted tar all over. In my amps I swapped tubes around and measured voltage differences for a little bit better DC balance. But separated cathodes sounds like a good idea.(I built a Williamson inspired amp once, using huge wirewound pots between the two output tube cathodes and ground. Was easy to balance but maybe not the last word in highend audio
It would be interesting to hear more ideas about how to make Quads safe for future use and longevity. I understand it is not a good idea to put a fuse between the HT center tap to ground?
Martin