test plug extension cable... voltage question

[Garydean]

Hi,

I'm making up a 7 wire extension cable which will connect an octal socket to a box with an octal socket for biasing output tubes. The stranded wire I'm looking to use is rated for 300VAC. Will that work if I have up to 700VDC present at the socked?

thanks,
Gary

[Enzo]

Probably, but don't sell it because you can't count on it. 300v insulation doesn't puncture at 301 volts, but the wire maker will not characterize the insulation as safe at higher levels than that.

REmember that 300VAC has peaks to 424v, so you could call it 424v wire I suppose.

And since any arc has to puncture two insulations to get from one wire to another, your 700v doesn't quite make it to that 848v.

Can't find 600v wire?

[Steve Conner]

With 700V B+, the plate voltage will peak out at nearly 1400V if you crank the amp with the thing connected. 300V rated wire could be getting a little sketchy

[Enzo]

Ouch, I would hope he wasn't playing the amp, just adjusting bias.

[Steve Conner]

Me too, but Murphy's law says if there's a way to screw something up, someone will find it

I'd probably add another grid stopper resistor at the "tube end" of the harness, too, to guard against parasitic oscillations. Those would probably generate pretty much the same high peak plate voltages if they got going.

[Garydean]

Thanks gents!!

The 600V wire is a bit more...cha ching. I'll keep searching.

G

[Garydean]

I'm now thinking of making my own cable out of hookup wire, then shrink tubing it. Would wrapping foil around the grid wire, guard against parasitic oscillations? Or what other wires should I wrap?

thanks,
Gary