Short piece of wire attached to pin 9 of a 12Ax7. What is your role?

[Pedro Vecino]

Does anyone know the function of this? This is a piece of wire connected to pin 9 of a socket. It is seen in Dual Rectifier, Roadking, Roadster...
Regards

[R.G.]

Google "dord".

[Mark Black]

I always like to refer to those as "Mojo wires". See them a lot in Boogies...

Seriously though it MIGHT actually have something to do with hum reduction or even oscillation prevention. You could try just picking up the loose end to see if it makes any difference at all, and all it will cost you is a dab of adhesive to put it back.

[R.G.]

Boogies are sensitive to the phase of the moon as regards oscillating or not. 8-)

[Old Tele man]

...pin 9 on the 12AX7 is the 'center tap' between the two filament heater ends, so it looks like a 'proviso' for possibly using some other tube with 6.3V filament instead of 12.6V filament.

...looks sorta like a "filament voltage 'lift' circuit" that's no longer implemented.

[anson]

Someone gave me some advice a while back about using a shortish trace connected to the heater and moving it around in the right place to use as a hum reduction method. Can't say weather it works or not.

[Robert M. Martinelli]

Boogies are sensitive to the phase of the moon as regards oscillating or not. 8-)

Ahh....thanks R.G.! So it's all about the phase of the moon.....For a moment I mistakenly thought those wires were short antennas to tune the amp to some alien entity brain's frequencies and use them to generate some odd (strange) harmonics in the amp by additive synthesis.....

Cheers

Bob

[Pedro Vecino]

Dual Rectifiers are very sensitive to the oscillation in pushed mode (first channel). These pieces of wire are on V2 and could have relation with it. Yesterday I had none but right today I have received another. When I open it I will try to orient it differently...

[J M Fahey]

Remember to wrap your skull in tinfoil before doing that, or Aliens could find you're messing with their cleverly disguised brain disrupters.
Ah !! y me olvidaba !!!! Aguante España !!!! Feliz Mundial !!
Y cuídennos la Copa, que la próxima es nuestra !!!

[defaced]

What happens when you lift the wire?

[R.G.]

Don't cross the beams!

[R.G.]

Seriously, though, from the picture it looks like the wire lays right across two coupling caps. I think the "induce some hum cancellation" is probably most accurate. Glued into that position, it radiates 3V of 60Hz AC. As close as it is to the caps, it has a good chance of coupling some of that into the signal path.

The best test is to remove it and see if hum comes up.

Radio amateurs were all familiar with the "gimmick" cap, two wires twisted together and clipped to length to tune the interwire capacitance. You get about 2pF per inch, depending on wire size, insulation thickness, air humidity, phase of the moon, etc. This looks like another old amateur radio trick, maybe.

And it's cheaper than making the circuit hum-immune, or inducing the right hum cancellation somewhere else. I suspect that the wire is put in and trimmed to length to get just the right amount of cancellation in a listening test.

Just a theory. Could happent that way. Your mileage may vary. I'll respect you in the morning.

[Old Tele man]

...I was (jokingly) gonna call it a "one-wire" gimmick, but chickened out.

[loudthud]

Does this amp have a DC Heater supply on the preamp? Many amps built on Printed Circuit Boards use DC heater supplies and series connections to eliminate hum pickup by all the circuitry on the board.

[oc disorder]

Most Boogies only have V1 running with a DC heater.
Some have V1 + V2 on DC.
Having all that gain no wonder they're temperamental.
It's amazing they dont implode in a burst of feedback !