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Springtime for ubilicals and tubeheads



 
 
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  #1 (permalink)  
Old October 6th 06, 10:58 AM posted to uk.rec.audio
Andy Evans
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Posts: 673
Default Springtime for ubilicals and tubeheads

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.


I was just doing a standard calculation as for capacitors - usually
about 1.4 to 1. Why is it different with connectors?

I picked a nickel plated NATO style connector 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)

I'll look again at Amphenol and the above - they looked expensive in
the Farnell catalogue. 70 euros is quite a lot, 32 is better. The
Speakon 8 way comes in cheaper and is more available, plus Dave made
the excellent point it's shrouded and so no danger on the amplifier end
from B+ caps. Doesn't matter with a preamp, but worth considering with
a three stage amp where to put the smoothing.

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

It wouldn't have to be - it would only need to supply low voltage low
current filaments. The bigger plug would do the B+. Both connections
would have to be earthed. And, as Iain says the one with the B+ would
have to be screened.

  #2 (permalink)  
Old October 6th 06, 11:20 AM posted to uk.rec.audio
Iain Churches
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Posts: 617
Default Springtime for ubilicals and tubeheads


"Andy Evans" wrote in message
oups.com...
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.


I was just doing a standard calculation as for capacitors - usually
about 1.4 to 1. Why is it different with connectors?


Odd isn't it. perpelexing too is that the same connector has different
ratings for different uses (military, broadcast or domestic)

I'll look again at Amphenol and the above - they looked expensive in
the Farnell catalogue. 70 euros is quite a lot, 32 is better. The
Speakon 8 way comes in cheaper and is more available, plus Dave made
the excellent point it's shrouded and so no danger on the amplifier end
from B+ caps.


That still may not be enough. You may well find that you are required
to have no DC at all on the chassis connector pins when the cable
connector is removed.

Power amps with separate psu are quite unusual these days. I have a
feeling that the safety regs might well be the reason. Solutions that were
common place in the 60s and 70s, like for instance the octal connector
between psu, amp and preamp, are now strictly forbidden, as are fixed
mains cables, and any other mains connector except the IEC type (with
the possible exception of the Speakon, I am not sure)

You have to be very wary. If your neighbour's world champion, best of
breed Rottweiler bites through your DC cable, it could cost you a pile
of the elusive spondoolicks.

Iain


  #3 (permalink)  
Old October 6th 06, 11:46 AM posted to uk.rec.audio
Andy Evans
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Posts: 673
Default Springtime for ubilicals and tubeheads

That still may not be enough. You may well find that you are required

to have no DC at all on the chassis connector pins when the cable
connector is removed.

that would indicate all smoothing in the PSU box. Can be done.

Power amps with separate psu are quite unusual these days. I have a
feeling that the safety regs might well be the reason. Solutions that
were
common place in the 60s and 70s, like for instance the octal connector
between psu, amp and preamp, are now strictly forbidden, as are fixed
mains cables, and any other mains connector except the IEC type (with
the possible exception of the Speakon, I am not sure) You have to be
very wary. If your neighbour's world champion, best of breed
Rottweiler bites through your DC cable, it could cost you a pile of the
elusive spondoolicks.

Two monobloks is looking like the easy solution. I have all the
amplification and PSU stages on seperate top plates, so can plug them
into any chassis - stereo, mono. whatever. I was thinking of a seperate
PSU for development purposes, to try out different valve circuits, but
I can do that in-house and then just construct the final units as
monobloks. Not sure what to do about the preamp - that's an easier
situation as you found.

  #4 (permalink)  
Old October 6th 06, 12:08 PM posted to uk.rec.audio
Iain Churches
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Posts: 617
Default Springtime for ubilicals and tubeheads


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

That still may not be enough. You may well find that you are required
to have no DC at all on the chassis connector pins when the cable
connector is removed.


that would indicate all smoothing in the PSU box. Can be done.


Well, I thought it better to decouple at the amp end of the
umbilical with a pair of 220µF electolytics, and so used a relay there also.

Power amps with separate psu are quite unusual these days. I have a
feeling that the safety regs might well be the reason. Solutions that
were
common place in the 60s and 70s, like for instance the octal connector
between psu, amp and preamp, are now strictly forbidden, as are fixed
mains cables, and any other mains connector except the IEC type (with
the possible exception of the Speakon, I am not sure) You have to be
very wary. If your neighbour's world champion, best of breed
Rottweiler bites through your DC cable, it could cost you a pile of the
elusive spondoolicks.

Two monobloks is looking like the easy solution. I have all the
amplification and PSU stages on seperate top plates, so can plug them
into any chassis - stereo, mono. whatever.


Now that sounds like an excellent "modular" idea, Andy.

I was thinking of a seperate
PSU for development purposes, to try out different valve circuits,


That's what I do. I have a Solartron regulated bench PSU 600V at
0.5A plus heaters and a bias tap. I also have a separate Farnell reg
supply 10A at 10V for heaters, plus another 100V at 100mA which I invert
as a bias supply. With clean DC you know that your development modules
are as good as they can be.

but
I can do that in-house and then just construct the final units as
monobloks. Not sure what to do about the preamp - that's an easier
situation as you found.


Yes indeed. When you get down to 265VDC things are not quite so
problematic. But you will still need the safety relay.

regards
Iain


  #5 (permalink)  
Old October 7th 06, 08:50 AM posted to uk.rec.audio
Jim Lesurf
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Posts: 3,051
Default Springtime for ubilicals and tubeheads

In article , Iain Churches
wrote:

"Andy Evans" wrote in message
oups.com...
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.


I was just doing a standard calculation as for capacitors - usually
about 1.4 to 1. Why is it different with connectors?


Odd isn't it. perpelexing too is that the same connector has different
ratings for different uses (military, broadcast or domestic)


The complications are due to variations in the anticipated range of
conditions of use, and in what effects/factors are regarded as setting the
limits.

e.g. For some items the main concern is a flashover or breakdown of the
insulation. The insulation may survive a 'brief' high voltage, but break
down after a given time if the voltage is maintained. Thus you may find
that an ac signal can have a higher peak level before breakdown than a
maintained dc.

Whereas for LF on some other items it may simply be that you need the
*peak* level of the waveform to be limited to the same level as the dc
maximum. Hence a factor of root 2 for sinusoids.

Some capacitors may suffer from internal dielectric loss dissipation
problems or plate conduction losses, so the max permitted ac might be
somewhat lower than the max dc. etc. Reason being to avoid overheating the
device. The expected environmental temperature will matter here as well.

Some connectors/cables may be rated for working under a pile of mud whilst
squaddies are jumping up and down on top of them. Others may not be
expected to cope with this. :-)


You have to be very wary. If your neighbour's world champion, best of
breed Rottweiler bites through your DC cable, it could cost you a pile
of the elusive spondoolicks.


Dunno if there us a mil spec for that yet... :-)

Slainte,

Jim

--
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Audio Misc http://www.st-and.demon.co.uk/AudioMisc/index.html
Armstrong Audio http://www.st-and.demon.co.uk/Audio/armstrong.html
Barbirolli Soc. http://www.st-and.demon.co.uk/JBSoc/JBSoc.html
  #6 (permalink)  
Old October 8th 06, 12:09 AM posted to uk.rec.audio
Andy Evans
external usenet poster
 
Posts: 673
Default Springtime for ubilicals and tubeheads

Since I've been looking at goodness knows how many connectors over the
last week, I have started to notice different ratings for AC and DC.
With capacitors one actual factory - in this instance LCR - informed me
that the ratio is about 1.4 to I so 250v becomes about 350vDC.
Presumably they've tested their products. But connectors seem to be a
different story - less than 1.4. I've seen things like 200vAC, 250DC.

It occurs to me that many of the connectors seem to quote 250vAC
because that's mains voltage. Must be some standardised coding. I
suspect many are capable of much more - e.g. Speakons - but just don't
bother to quote a higher voltage which they don't expect their product
to be used at.

Amphenol does seem to quote a voltage which is more in keeping with the
product, and I guess that "power" rather than mains connectors need to
be more specific, since all kinds of industrial and military voltages
may be required.

I did also come across some cheap and very useful connectors in the D
range - quoted for 750vDC. these have bugger pins than usual, and can
be bought either big pins only (three, eight) or mixtures of big and
regular pins. Made by Harting and can be found in the Farnell
catalogue. This looks particularly useful - cheap too.
http://uk.farnell.com/jsp/endecaSear...sp?SKU=1207587

  #7 (permalink)  
Old October 8th 06, 09:32 AM posted to uk.rec.audio
Dave Plowman (News)
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Posts: 5,872
Default Springtime for ubilicals and tubeheads

In article .com,
Andy Evans wrote:
Since I've been looking at goodness knows how many connectors over the
last week, I have started to notice different ratings for AC and DC.
With capacitors one actual factory - in this instance LCR - informed me
that the ratio is about 1.4 to I so 250v becomes about 350vDC.
Presumably they've tested their products. But connectors seem to be a
different story - less than 1.4. I've seen things like 200vAC, 250DC.


And many connectors have the same ratings for both. I'd guess it purely
depends on the actual testing and intended application.

If you look again at those BS 4343 Commando connectors, they're 'rated' at
110, 240 and 415v AC, but are similar in design and made from the same
materials. Indeed, the 415v three phase type has the pins rather closer
together than the 110v ones.

So most connectors tend to be specified to meet the safety requirements of
a particular application (other than extra low voltage) rather than their
physical peak voltage and current handling capabilities.

A good example is the Jones plug as used for pretty well your app on a
Quad II valve amp. It was obviously a satisfactory connector from the
electrical point of view since they don't fail - but the spec these days
wouldn't 'allow' them.

--
*Hard work pays off in the future. Laziness pays off now *

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




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