[Amps] What to do about 'Neutral' in HB amp?

[Roger Parsons]

I am most grateful for the replies received both on the reflector and individually. It seems I have to go into a bit more detail - sorry.

Firstly, I am indeed sure that the amplifier had neutral and ground cross-connected as originally manufactured. I have sent a copy of the original schematic to 'Goodguyham' who wanted 'proof', and would be happy to send it to anybody else if necessary.

This particular amp is very obviously a prototype, and there are a number of unusual features including a nightmarish mechanical design around the vacuum variables. I have no idea whether it is similar or otherwise to the PT-2500 or to other examples of the PT-3000.

The blower is 120V and has one side grounded and there is/was also an 'Agastat' which appears to be a time delay relay intended to keep the blower on for 3 mins after the amp is switched off. The tube filament is powered from an external DC power supply. I don't like either of these features. I have replaced the blower which is now properly mounted, the Agastat had disappeared before I got the amp, and I have found space for a filament transformer. It would have been best to have obtained 240V versions on these items, but I didn't.

I had firmly decided to use a four wire power connection, but must admit I have been rather swayed by suggestions received, and I think I will now wire the blower and filament transformer to the main power transformer centre tap. This means that I have purchased and spent some effort wiring the 4 way receptacle for nothing but hey! 

(SOOW wire is just too thick for me to use. Making my own using heat shrink could have been attractive, but I can't see how that could meet code or more importantly actually be safe against abrasion.)

I have tried to summarise. There are a number of other factors which have influenced my thinking but I'm sure many have had quite enough by this point.

73 Roger
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