Express 6v6. One power tube is getting very hot

[ampmike]

Hey fellas,my express was sounded good but It sits a lot and does not get played regurley.Im getting a thumping sound when I turn on standby to play. I got that to stop for awhile but one power tube is heading for red plate I'm afraid.It just gets much hotter to the touch than the second one ,I tried replacing the .022 coupling caps and it's still doing it. I've got a good set of tubes and really don't want to ruin them. Any other suggestions,thanks,Mikey

[Phil_S]

Are you sure it's the amp and not the tube? If you swap positions, does the red plate follow the tube or the socket? Maybe you'll get lucky and it follows the tube, in which case the solution is obvious.

If the problem stays with the socket, you've got to find the source of the excess current. I'd start by pulling the power tubes and taking unloaded voltage readings, measuring components to the extent you are able without desoldering, and seeing if you can measure OT DCR, which won't be perfectly symmetrical, but shouldn't be too far off.

[ampmike]

One thing I just checked is the screens are 409 on one tube and 215 on the other.

[ampmike]

Just tried it with another set of tubes. Full power same thing. I'm thinking maybe the 1k 5 watt is bad. The one resister maybe

[ampmike]

Just tried it with another set of tubes. Full power same thing. I'm thinking maybe the 1k 5 watt is bad. The one resister mayby. I can't get a reading on the cold tube resister. But the hot side I'm getting a number .

[Phil_S]

If you think you have an open 1.5K resistor, unsolder the end away from the socket, pull the tube, and check it for DCR. If it is open, you know what to do.
If not, I think it would be helpful to see a schematic of the PI and power tubes with voltages indicated or a voltage chart.

[ampmike]

Hi Phil,I found that the one screen resister 1k 5 watt was shot,I had a white cement one and now we're good.Do you have a source for the green ones.Rj was always my go too but he is very busy. The voltages were all reasonable or at least the same now on each tube but I'm wandering if there is a voltage chart for 6v6 tubes,hey thank you for your time ,I think it's sounding really good now.I may have stressed one of each power tube so I'm going to test them.Thanks again

[joeboo88]

Tubedepot has those green 1k 5 wat resistors.
Joe

[Phil_S]

I don't think your amp knows the difference if you have a sandblock 1K on the screens. It sounds good? It ain't broke, don't fix it.

[ampmike]

Yea your right,I build a nice marshall 4 12 with mojo watch tower celestions.It was a slant cab and really came out sounding ok but a old mesa recto cab 2 12 with V 30 is amazing with the Wecks.Mayby the with and depth i dont know but that setup is the best.I just goof around at home with it but its a lot of fun especialy when no one is home.