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

In article . com,
Andy Evans wrote:
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.

IIRC, the voltage ratings have more to do with the safety angle due to the
design of the connector rather than what it can handle insulation wise.

Is this for production or a one off? If a one off I'd be searching Ebay
for a suitable Amphenol.

--
*Few women admit their age; fewer men act it.

Dave Plowman London SW
To e-mail, change noise into sound.

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

Big oops!

Just looked at the picture again and it's not a standard D plug, but a
Sennheiser socket, and it is an output rather than an input.

Looking at the circuit, I see in that case it is cap-coupled and only
carries 200V AC.

Alarm bells rang when I realised the significance of the PS caps being
on the amp. That would mean that both plug and socket would need to be
shrouded so you can't touch either when unplugged, because both could
be live.

Sorry for my original misinformation...my only defence is that it is a
very unusual amp and it really does look like a D connector in the
photo.

cheers, Ian

"Andy Evans" wrote in message
ups.com...
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).

Morning Andy.
That's odd. Most connectors and relays have a much *lower*
rating at DC than AC.


Possibly the option of two.
e) common part, not likely to become obsolete

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.

Firstly you have to find a connector that is rated for the
DC voltage you need, *in a domestic environment* Some broadcast
and studio connectors, are rated at 1500V industrial but only 70V domestic.
For your private use, you have a greater freedom of choice, and are
only dependent upon what an insurance company will accept. But if
you plan to sell to the general public then the situation is different.

Secondly, unless you can buy them from scrap equipment, good connectors
never come cheap. For the purpose you are considering, I picked a nickel
plated NATO style connector as show in the pic below:

http://www.kolumbus.fi/iain.churches...earPanel01.jpg

http://www.kolumbus.fi/iain.churches...earPanel02.jpg

These are available in 9,12,16,21,26 way. The working voltage
decreases as the density of pins increases. RS part number for the
9 pin male plug is 234-685. They cost about Euro 17. The matching
female connector for the PSU end, and also the cable connectors are
about the same price. So a complete set, of chassis and cable connectors
comes out at about Euro 70.

Both the Hirschman and the Amphenol NATO connectors are much
cheaper at about Euro 8 for the 8 pin. They are either grey or olive drab.
That is not a lot of money for such a good connector. (Euro 32 for a
set)


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

I have an uneasy feeling that the D connector female is not sufficiently
touch-proof for safe use above 70VDC.

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

The 8 way is never used for speakers, so that would be the obvious choice.
Also take a look at the Bulgin Buccaneer range.



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.

There used to be an XLR with three insulated pins designed for DC and also
mains use. I am told it is no longer approved above 70V

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

Both safety and reliability are involved here. As Dave points out,
connectors are rated at what is considered safe, not maximum
voltage or current. It seems to me this is not the place to economise.

I would go for two (different) multipin locking NATO connectors.
I am not sure about the UK, but in this part of the world you must
also make provision for the DC to shut off if either end of the
umbilical cable is removed. I used a ground link and a safety
relay for this - so two more pins required. You do not need to shut
the psu down, just switch the B+ into a dummy load or OC
(if the 'lytics will stand the extra voltage)

Also, care must be taken with the choice of cable for the umbilical.
For use here in Scandinavia, I was told that it must be as short as possible
to connect the two pieces of equipment, and must under no circumstances
be long enouigh to touch the ground and therefore get caught under table
legs etc. Also the cable must be armoured with an outer braded screen
connected to ground in addition to the 0VDC (black) on the inner.

You can see the cable which I used, and subsequently shortened to
30cms, at:

http://www.kolumbus.fi/iain.churches...02+PSUrear.jpg



Regards
Iain

"Ian Iveson" wrote in message
. ..

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.

That's probaly the round plated connector I mentioned to Andy elsewhere in
this thread. the terminal pins have solder buckets, it needs no crimping
tool. The fixing holes are 2.5mm. I usually drill them out to 3mm.
For such a high quality connector, I don't think Euro 17 is expensive.

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

My amp needed 10A DC for heaters, elevated 100V above ground.
I split this over two pairs of pins.

I spent some time wondering about high unregulated current passing through
the same conduit as the carefully-filtered HT and bias supplies.

Same here. Once I had the interconnect cable I was planning to use,
I wired the B+ and Bias to inner wires, and kept the heater wires on the
outside. The flexible armoured cable had both an inner ground wire
and also an outer braided shield. With DC heaters in a 50W PP amp,
I managed a noise floor of 150µV ( SNR about 105dB)

Iain

In article ,
Iain Churches wrote:
Most connectors and relays have a much *lower* rating at DC than AC.

Relays and switches - yes, due to the arc which can happen when they break.
But I've not seen a connector that gives different ratings for each.

--
*Husband and cat lost -- reward for cat

Dave Plowman London SW
To e-mail, change noise into sound.

"Dave Plowman (News)" wrote in message
...
In article ,
Iain Churches wrote:
Most connectors and relays have a much *lower* rating at DC than AC.

Relays and switches - yes, due to the arc which can happen when they
break.
But I've not seen a connector that gives different ratings for each.

Look at RS 234-685 the standard plated NATO connector.
380VAC but 200VDC according to the German maker's catalogue
spec.

Iain

For a start - thanks for the helpful suggestions, much appreciated. In
response to Dave P, not just a one-off so I need something I can
re-order from usual suppliers. Amphenol is nice, of course, but
expensive and nothing on ebay in the UK.

Your point about capacitors in the amp chassis is extremely perceptive.
I hadn't decided how to do this - one B+ supply to the chassis and
further smoothing there or several B+ supplies from the PSU. As you
say, this makes a big difference. Any capacitors in the amp chassis
would rule out XLRs. It would, however be possible to use Speakons. The
8 pin speakon was used by Beard audio as an umbilical, so he obviously
did a bit of research and had that idea. I have to say it's tempting.
Plug is big though. It's again a bit expensive - would be £19.45 for
two sockets and two plugs. Still, could be worse.

4 pin speakons cost £6.63 for two sockets and two plugs. That's very
tempting. Would have to be clearly labelled PSU though.

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

Yes, that's exactly what I do.


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.

All the suplies will be DC, as you say. No choice with DHTs.

I think I'm going for twin supplies rather than one connector. Most of
the filaments are very low voltage low current - something like 4 volts
at 120mA max. The output valves if 2a3 would be 2.5v at 2.5A. Would
need four connections for those.