1N4007 power tube socket + 1 Ohm bias resistor question?

[JamesHealey]

When using a 1R resistor on the cathode of the power tubes in an express,
can you place the 1N4007 on the 1R or do you have to connect the 1N4007 diodes straight to ground.

Just thinking from a cosmetic point of view, at the moment i'm not running any 1N4007 on the power tubes but I want to.

Cheers,
James H.

[Bob Simpson]

Hi James.

I remember on the first real mod I did, building GP's McIntyre Bluesmaker out of a Bassman, McIntyre had both, but
for different reasons.

I think the chain of 3 1N4007s from pin 3 to ground is to protect the tubes from flyback voltages, and the single 1N4007 across the 1R was to protect the 1R if a tube shorted out.

I've used them both or individually with no bad effect.

I've heard different diodes color the sound differently, but have not
experienced that myself.

Good luck.

Bob Simpson

[paulster]

I do them to ground because you never know how much current they might be called on to dump, for the instant that they are conducting.

I use an M3 tag on the power tube mounting screw, since it's pretty well moot whether it connects to a star ground or the chassis ground for this particular purpose.

[jaysg]

You might be better off with a 1 ohm resistor going open with a shorted tube.

[paulster]

If you get a shorted tube you'd like to think that the HT fuse would fail before relying on a resistor to open up, since unless it is a fusible resistor, the failure method is undefined and could result in a fire.

The 1N4007 diodes are to protect against flyback voltages in the OT, so it would make sense if these begin to conduct current that they'll take it around the cathode bias sense resistor rather than through it since it's imperative that these do dump current to save the OT rather than risk the resistor failing and not saving the OT.

[JamesHealey]

cheers paulster makes sense..