Remote Power Supply: A Stupid Idea?

[SRMcGee]

Folks:

Please advise the newbie: I am considering building a tube preamp with an outboard power supply, but am questionning the wisdom of the idea. I have a nice 2-box chassis to work with, but am concerned about the demands placed on the umbilical running between the two enclosures. At very least, the umbilical will need to carry the high voltage lines for each channel and the 6.3v filament lines (there will be one for each channel) will each need to carry about 2 amps.

I'm imaging an awfully heavy gauge wire will be needed, and the umbilical will end up pretty bulky.

How dumb an idea is this?

Thanks,
Scott

[SY]

It's actually done pretty regularly and is good practice. The umbilicals really aren't that bulky. The thing to be careful of is that no high voltages appear on exposed pins when the preamp is unplugged from the PS- you want only females coming from the PS box.

[SRMcGee]

SY:

Hmmm.... I had been thinking about using those 9-pin computer "D" connectors and making my own umbilical. What gauge wires do you recommend?

Thanks,
Scott

[SY]

Check the voltage ratings on those connectors first! I like to use the Amphenol circular ones.

[rdf]

Consider instead a multi-pin Amphenol style or equiv as shown on Mouser's site:

http://www.mouser.com/amphenolind/

I personally wouldn't use a sub mini-D for the high voltages and currents (heaters) of tube equipment.

Edit: Seconds too late!

[tubelab.com]

You should make sure that the connectors that you are thinking about using can take the voltage and the current that you are going to apply to it. I am not sure that the computer connectors were ever intended to handle this much electricity, although I did see some rated for 5 amps and 1000 volts in the DigiKey catalog. If I were doing this I would use a larger connector. In my 845SE amp I used "Cinch Jones" connectors. They have lived for two years with 1100 volts on the HV pins, and 3.25 amps flowing through the filament pins. These connectors were in the DigiKey catalog, but now the catalog says that they are only available online.

I use "test probe wire" for the HV leads, and 18 guage hookup wire for the low current filaments. I use 16 guage for the 3.25 amp filaments. You can't solder this to D connectors.

[SRMcGee]

RDF:

The Amphenol connectors do look nice, but it looks like a set of four (2 box mounted units and 2 for the umbilical) will run between $65 and $70, depending on the number of pins (probably 10). Is there a cheaper option, or is this "penny wise / pound foolish" thinking?

Regards,
Scott

[EC8010]

Yes, there's an option that only costs half as much and is more reliable. Don't have a connector at the pre-amplifier end. Make the cable captive. You know where you're going to put the two boxes, and you know how much cable you need. Use a female connector on the power supply chassis and a male connector on the lead from the pre-amplifier.

[Sherman]

Originally posted by SRMcGee
RDF:

The Amphenol connectors do look nice, but it looks like a set of four (2 box mounted units and 2 for the umbilical) will run between $65 and $70, depending on the number of pins (probably 10). Is there a cheaper option, or is this "penny wise / pound foolish" thinking?

Regards,
Scott

You could look at Molex connectors. Not as nice or as nice looking as the Amphenols but you could do it for about $10US.

You might also consider not putting a connector on the PS. Just run the wires directly out of the chassis (through a bushing or grommet) and have a female connector on the end of the umbilical and a male chassis mount on the amp chassis.

[Dr. Photon]

Cinch-Jones connectors would work fine. Be sure to have the female end on the power supply. If it were my design, I'd have a male connector and umbilical comming out of the preamp, and the power supply would have the female socket on it.

I would also have one last filter stage in the preamp itslef, or at least the fiter capacitor for the first node of the power supply in the preamp (which would power the output stage).

Be sure that there is a diode in series with the +B input on the preamp chassis, since otherwise there would still be some voltage on the connector if the preamp and power supply were disconnected while running. Also be sure to add bleader resistors in Both chassis.

I would isolate the filament leads from ground in the preamp chassis, you can connect teh CT of the filament winding to ground or do whatever you like doing with your filaments in the power supply chassis. I recommend regulated filaments.