Separate power supply - Umbilical Cord

[marcutan]

Separate power supply - Umblical Cord

Hi,

I am building a separate power supply for my 2a3 SET amplifier.
What is the best connectors and wire (gauge, stranded/solid?) to build the umbilical power cords?

I am thinking of:

a) XLR 4 pin for the bias voltages (300v, 280v). 23 Gauge solid silver cable
c) XLR 7 pin for the heater supply (2 pin each for the 2x 2a3 Heaters and 2 pins for the driver heater). 18 Gauge stranded copper.

Should I add a copper shield then a PVC insulation over the power cord?

Thanks,
Marcus

 

[astouffer]

Don't use solid wire for cables that need to flex and silver wire in this application sounds like a waste. The connectors sound like they will work fine but I'm sure someone will get upset about the voltage being too high.

 

[xiphmont]

Agreed, go for the superior mechanical capabilities. Make sure the connectors are rated for voltage/amperage. Stranded wire with more/finer strands is more durable when flexed, but the biggest practical difference will probably be the quality of the insulation (where good insulation is flexible, durable and long-lived).

Silver offers you nothing over copper here. Unless you think it's pretty for some reason and have the money to waste^H^H^H^H^Hspend ;-)

Copper shield on the umbilical gets you absolutely nothing.

 

[Evenharmonics]

These plugs may do the job.

 

[mach1]

Do a search - the topic has already been covered extensively on this forum.

 

[ak_47_boy]

Ya, use stranded copper with proper plugs. Silver power cables are pointless, silver signal cables are IMO also pointless but thats debatable.

 

[TheMG]

I don't really see many applications where silver cable would be any benefit at all especially when you consider the added cost. I mean, we're talking about tiny differences in resistivity.

FWIW:

Silver: 1.59×10−8 Ω-m
Copper: 1.72×10−8 Ω-m

 

[marcutan]

Thanks

Thanks for all the help. The Cinch plug and socket sounds like the way to go. I will also stick to stranded copper with flexible insulation. It is interesting to learn that the copper shield is not helpful here.

Do we need to twist the copper wires? The heater voltages and biases are all D.C.

 

[astouffer]

Twisting the wires can't hurt. It may help with crosstalk being that the filaments are part of the signal chain. I'm surprised that cinch connectors are still being made, they have been around forever.

 

[pftrvlr]

I ended up with 8 pole speakon NL8MP/NL8FC connectors. They are sturdy and reasonably priced in EBay. This cable is heavy gaugue and good fit for the connector:

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&rd=1&item=150209409947&ssPageName=STRK:MEWN:IT&ih=005

 

[xiphmont]

I ended up with 8 pole speakon NL8MP/NL8FC connectors. They are sturdy and reasonably priced in EBay. This cable is heavy gaugue and good fit for the connector:

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&rd=1&item=150209409947&ssPageName=STRK:MEWN:IT&ih=005

Ergh, well, just be careful those connectors are never mistaken for use with actual speakers! You can probably key them somehow to prevent an accident (I've *never* seen speakon used for anything else, I'd never think twice about "oh, that's a speaker port").

Otherwise, good choice! That cable is the kind of actually useful overkill we like to see. 13AWG... lordy. 13AWG is thick enough to power many arc welders...

 

[pchw]

I have some 10 gauge Belden speaker cable that has printed words saying for audio only, not for power connection. I think it is due to the insulator used. Do these 8 conductors speaker cable have the same limitation in high voltage use?

Thanks!!

 

[protos]

Funnily enough without looking for exotic plugs and sockets if you look at the ratings of good computer multipin connectors you will see they are perfectly suitable for high v ie 750v and quite a few A.

 

[andyjevans]

8 way Speakons were used by Beard Audio for umbilicals. Good sturdy connectors, and also touchproof. Remember that if you have any HT capacitors in the chassis you'll get a shock off the plug if it's a male one. Touchproof protects against that.

I wouldn't use cinch because it's rectangular and why make life difficult? Plenty of round plugs around you can make cutouts for with hole saws.

As for XLRs, I don't see why not - they're cheap and good. The ones that are easiest to get are 4 and 5 way. Obviously not 3 way. So 5 way for HT and earth plus any minus voltages etc., and 4 way for filaments, remembering that filaments tend to come in pairs and have higher current, hence the larger 4 pins.

6 way XLRs are possible but expensive unless you buy a pile cheaply. 7 way XLRs are all but extinct so I'd forget those.

Don't forget D connectors - very handy for multiway connections!! Not round holes though.

Many will recommend the excellent Amphenol range - if you have deep pockets!!!

 

[billr]

Hi

I worry about using the same style plugs and sockets for umbilicals as used for speaker sockets/plugs etc. Personally I wouldn't.

I am designing a stereo PP amp at the moment, and plan to house the power supply in a separate chassis. I will use separate umbilical cords for the HT/Bias and the heater supply.

I also use male plugs on the cord at the PSU end, and a female inline socket at the amp end. No exposed pins with nastiness if the psu is turned on without plugging in the amp.

I am using relays to power the HT and heater supplies, so, i include a low voltage loop up the HT PSU line so that if some bozo uplugs the HT the PSU turns itself off.

I like to be safe when doing all this stuff.

I built a dual HP PSU for running things up, it's got 250 ~ 450 volts, regulated and variable, up to about 60ma each, the regulator and control stuff is in a sep chassis from the Transformer which is massive, i put in loops in the cords there too.

you may think other wise.

Kind rgards

Bill

 

[kevinkr]

I use AMP CPC and I buy them here for very reasonable prices. I've used them for over 10yrs at voltages of up to 500Vdc..

http://www.action-electronics.com/ampcpc.htm

 

[andyjevans]

Those AMP connectors certainly look the business and are surprisingly good value!

Another solution not mentioned is the DC Power 2 way connectors, 2.1 and 2.5mm. For those using DHTs these can be quite handy, since they are used by ready-made 12v DC power supplies which can be bought very cheap, especially surplus. You can standardise your small signal DHTs to run off 12v and put the appropriate voltage and current regs for each DHT in the chassis. That way you have kind of a universal option for running filaments.

To be really cute you can use a 2.1mm connector for 12vDC and a 2.5mm connector for 6vDC, as would be better for a 26 for instance. That way you can't connect 12vDC up to a 6vDC socket. That's what I'm doing!

Upsides of these are ready made leads, adapters etc

Downside of DC Power connectors is they are not a very secure fit, though no doubt fine for stationary units. Also I don't think I'd run an 845 or 813 off them.

 

[Gordy]

Difficult to comment exactly as I don't know your system and circuits, so this is just a guide to a good starting point for a professional job:

Preferably one umbilical, not two. (Less chance of ground loop problems).

Female terminals on anything with a voltage on it (i.e. female at fixed connector at outlet of power supply box, and at the other end of the umbilical).

Circular metal shell twist-lock connector, see ITT-Cannon / Amphenol, etc.

Use a relatively heavy gauge earth wire to audio ground point / star in amplifier box, typically 10 Gauge.

Copper stranded conductors. Individual wire gauges chosen according to:
a) calculated peak current x 1.5,
b) expected temperature in centre of bundle at max expected ambient temperature,
c) desired impedance.

Wire insulation chosen according to maximum voltage rating and expected temperature.

Twist conductors carrying equal and opposite signals, and screen them as pairs. Ideally use a microphone cable for this if you can find one with the desired gauge / impedance / voltage ratings, etc.

Keep the overall wire bundle together by using two turns of tape every 80-100mm.

Use overall screen braid over the bundle, and ground it to the metal case at the amplifier end.

Use a flexible overall heatshrink tube over the completed screened wire bundle. (I like Raychem DR-25, but may be hard to get in small quantities).

Add additional overall mesh abraison protection, if you want to look flash.


Good luck,
G.

 

[tms0425]

I use AMP CPC and I buy them here for very reasonable prices. I've used them for over 10yrs at voltages of up to 500Vdc..

http://www.action-electronics.com/ampcpc.htm

I've used these long ago and they're nice connectors. Just curious, since there is a wide variety, which flavor of contacts do you use typically (one for all seasons)?

My current Aikido project has dual mono 300v B+ low current, and 2A heaters. I looked at the 9-pin for general usage, with 20-24 gold that could be parallel'd if necessary. The 16-18g ones appear to be tin/lead plated but would be more robust for bigger power.

Tom

 

[xiphmont]

I've used these long ago and they're nice connectors. Just curious, since there is a wide variety, which flavor of contacts do you use typically (one for all seasons)?

My current Aikido project has dual mono 300v B+ low current, and 2A heaters. I looked at the 9-pin for general usage, with 20-24 gold that could be parallel'd if necessary. The 16-18g ones appear to be tin/lead plated but would be more robust for bigger power.

Tom

Gold plating gives you only one thing: corrosion protection. And that stops when the thin gold layer wears through

Tin/Lead is not to be scoffed at. Unfortunately, lead is being phased out of nearly aspect of electronic production, so I don't think you'll be able to find it for long if at all anymore. Take the lead out and tin is nothing but trouble ;-)

Yeah, OK, this wasn't actually useful to you, but I like talking and I'm bored. Just waiting for the afternoon coffee to hit...