Andy Evans wrote

I'm trying to decide on that age old question of what connection to
make from seperate PSU chassis to main valve amplifier chassis. I'm
thinking in terms of a shared PSU and two monobloks, so connectors
would only have to take the power to one amp. Criteria I decided
were
essential we
a) low cost (so no Amphenol connectors)
b) potentially large number of pins (at least 15)
c) locking (so can't get pulled out by accident)
d) at least one connector must safely take 360Vdc (equals 250v AC
rating). Possibly the option of two.
e) common part, not likely to become obsolete

first I agonised over one cable or two, and decided one cable would
require too high density, be hard to wire, would be expensive, and
would be an uncommon part. Amphenol out the window.

next I did the calculations for number of connectors. Since I'm
planning for three stages of DHTs and my system is balanced, this is
what I found:
* 12 connections for the filaments of 6DHTs.
* earth
* -15vDC for CCS
* one B+ or maybe two.

that's a minimum of 15 connections. So my eye fell on D connectors.
Relatively easy to wire up and available in 15 way which is nicely
compact. Some are rated at 500v even, so a single 15 way D connector
is
not impossible.
but while I was happy with the filaments and the -15v supply on D
connectors, I would really like better contacts for B+ and earth. My
two choices for an added connector we
a) speakon plugs in 2,4,8 way
b) XLRs
Speakons are cheap in four way but expensive in 8 way, so 4 way
remains
a possibility. I'm not quite eliminating them but I'm a bit put off
by
the following:
1) they're bigger and stick out more than XLRs
2) some idiot might plug a speaker into the PSU box

So XLRs. they offer the possibility of using 4,5,6 or 7 way. Now, I
spoke to Neutrik about the voltage rating for these, and it's a bit
more complex than you think. Some of their paperwork specifies 50v
for
the whole range, some specify 150v, some specify different voltages
for
different connectors. The sales guy in the UK quoted me 250vAC for
3-6
way and 125VAC for the 7 way. Not much agreement here, and the
unbranded Chinese ones have no voltage rating. In terms of
availability
the 5 ways are common, 7 quite rare and gets eliminated because
won't
handle the voltage. Four and six way are more unusual, and six way
is
much more expensive. Four way can be had in cheap unbranded. So I'm
thinking 4 way right now, with the 15 way D connector, because this
gives the biggest pins and widest spacing so with unbranded the
chances
are they're OK for 250vDC, or at least more likely to be than the 5
way.

I hope you've followed all this. So any suggestions? Anything I've
left
out like BNC for just the B+ (high voltage)? Never used BNC but it's
locking at least. Is my above reasoning reasonable? Bright ideas?
Andy
I have a similar concern about pin-headers.

The cover of Morgan Jones' "Valve Amplifiers" had a picture of what I
assume is his electrostatic earphone amp with what looks like an
ordinary 11-way D plug on the front marked "high voltage". HT is
around 1000V. I can't see why 11-way was necessary in his
case...perhaps he left vacant pins around the HT connections. Latest
edition has a different picture.

I used 9-way screw-lock connectors with leading centre ground for each
of my monoblocs, after searching for weeks through catalogues
detailing a zillion military/industrial style jobbies. The big problem
was finding ones that don't need expensive dedicated crimping tools. I
probably have the part numbers somewhere, but nine pins isn't what you
want anyway, and they are expensive. But very nice solid plated brass.

I was worried more about current than voltage, so I connected power
valve filaments in series and drive them with a current source.

I spent some time wondering about high unregulated current passing
through the same conduit as the carefully-filtered HT and bias
supplies. Regulating all the filament supplies relieved the worry, but
I don't know if it was actually worthwhile.

What remains a problem for me is the cabling to the connectors. I
wanted something slinky and svelte but don't know how with so many
wires, so what I have is rather stiff and unwieldy. What will you use?

Using two umbilicals to each monobloc would have been easier in
several ways but I wanted to avoid adding to the rat's nest.

BNC for HT? Is it possible to arrange that so that the live connection
can't be touched when unplugged?

cheers, Ian