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
Yo, Andy, the trickiest consideration is actually where your caps are
and how they're discharged and how fast, so you don't have big joule
lurking on exposed pins. Traditional practice is to put the last
decoupling cap for each section split-up amps right next to the signal
tube rather than on the power chassis...
I've been there, building amps at heavier than me 100Kg to avoid the
problem of connectors, then splitting them when my back complained,
buying expensive milspec connectors and their tooling and finding them
not always as sturdy as "military" would imply.
Couple of possibilities:
1. Bulgin used to make connectors up to eight pole that were shielded
on both plug and socket. They were black and reasonably small (like
their round 3 point chassis socket and plug sets, not as small as the
modern micro Buccaneer connectors which I haven't tried) and usually
carried in the electrical power connection sections of catalogues. They
were cheap. I can't find them now in the catalogues I looked to get the
parts numbers for my best tip, below, but I had some that an old ham
gave me and they were brilliant. Maybe some surplus catalogues still
have them.
2. One Speakon that is shielded and locking and not too expensive, and
even looks like audio gear, all the good reasons why I used it to slave
the 300B booster/control amp to my Millennium End 80W SE amp's SV572-xx
power amp section, is in the RS catalogue (p104 of the 2004/5 Irish
catalogue). It's the one with the red ring. There's a 4 pole version
that is gold plated (which I have used as plug-in switch on other
occasions) for about EUR 7 per set, and a tin plated 8 pole version for
about EUR 11 per set, in both cases plus taxes. The RS catalogue
numbers for the 4 pole are 171-102 and 171-118, and for the 8 pole
215-6414 and 215-6420. Maplin also carried them the last time I bought
some and compared prices.
HTH.
Andre Jute
Visit Jute on Amps at
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