On Sun, 4 Oct 2009 01:23:01 -0700 (PDT), Andy Evans
wrote:

Hello again,

Thanks for the contributions. I'll answer the questions first! David
Looser - nothing is either arbitrary or illogical here. The connectors
are chosen for the following criteria:
1) They are cheap and widely available. So Don and Dave - yes, plenty
of Lemo and Amphenol to drool over! You have my sympathies here! But I
arrived at Amphenol AP because it was a much cheaper option for the
voltage required, while being available from most suppliers.
2) They carry voltages within their voltage rating. Here, David, note
that XLRs are now rated as 50v. They were rated at 300v or so but have
been re-rated in conformity with newer regulations, so XLRs are now
not an option for high voltages. So they are used for filament
voltages. Speakons are rated 300v. They could no doubt carry more but
I'm using an Amphenol AP connector because it's rated 660v.
3) They are not confused with other connectors. So 3 pin XLRs are out
for power supplies, 4 and 5 pin are possible. Speakons could
theoretically be an issue but they are only used on the power supply
where they are fixed to the chassis. There's no power on the signal
chassis end so you couldn't connect a speaker to it unless the amp had
no power to it.
4) They are safe in use - fingers can't touch live parts. Speakons are
nice here because shrouded, but they don't have the voltage rating for
490v. Yes the backs unscrew, though when you screw them up tight they
are pretty hard to unscrew. A theoretical hazard maybe, but well
noted. Thanks for pointing that out, Phil.

So having arrived at the current solution by careful logic, it's a
good question "why change it"! I don't have to - it works perfectly
well. The amphenol connectors are nice and easy to use, though a
little large.

The advantages of a coax connector is that I could buy already made up
leads, which would save time. Now this is where Phil is very
informative - thanks Phil!
None of the readily available types are even vaguely safe as they
allow finger contact with the core terminal. This was indeed my
question. I haven't handled these connectors so I'm only going by
photos - you can't handle a photo so I don't know what can and can't
be touched.

So you reckon - as above - that all these coax connectors could be
touched? That would rule them out really if that's the case.

So again Phil says stick with the Amphenol. Earth and HT connect
simultaneously, earth is a nice big size. Cable is rated for 1,000v.
Of the 4 connections two are for HT and earth, and one is for fixed
bias if used, so typically -30v or something. So I do have one
connection available. So what is the suggestion of carrying the ground
connection back to the PSU? How is this implemented and what's the
advantage?

andy

You can use that one spare connection for ground, but is that
something different from the one you already nominate as Earth? Not
too clear about that.

d