OK..I changed tubes and the same problem occurs. lightning

[Adambomb]

I had tube red-plate last week. I just got 4 new power tubes for my DR and STILL the same thing. I turn the amp on..tubes warm up...then hit the standby switch and ONE TUBE JUST GOES CRAZY. Blue lightning type stuff inside the tube and the amp hums.

WHAT THE HECK IS THIS? It's gotta be within the amp. I have a 2002 Dual Recto. Please help.

 

[212Mavguy]

Hi Adam,

By now you probably have had some advice to take your amp to the tech, that would be the best thing to do. Another, dubious choice would be to run the amp on only one pair of power tubes. If the amp were mine and I was happy with it in all other ways I'd get it fixed and keep it. Stuff happens. Perhaps this is a leftover from a previous accident, wasn't it you that had your amp fall to the ground?

 

[Adambomb]

Hi Adam,

By now you probably have had some advice to take your amp to the tech, that would be the best thing to do. Another, dubious choice would be to run the amp on only one pair of power tubes. If the amp were mine and I was happy with it in all other ways I'd get it fixed and keep it. Stuff happens. Perhaps this is a leftover from a previous accident, wasn't it you that had your amp fall to the ground?

Thanks for your info. Yea, it runs good with the 2 matched middle tubes. But the other tube that redplated still has sparks in it. I guess I messed up that tube. I gotta practice tonight so I am gonna run only the 2 inner power tubes and remove 1 rectifier tube.

 

[stokes]

Sounds like you lost bias voltage at the socket that caused the redplating/sparks.Without bias voltage the tube will go into a runaway condition when high voltage is applied,killing the tube almost instantly.I'd have it checked by a qualified tech.

 

[Adambomb]

Sounds like you lost bias voltage at the socket that caused the redplating/sparks.Without bias voltage the tube will go into a runaway condition when high voltage is applied,killing the tube almost instantly.I'd have it checked by a qualified tech.

Yea, I took it to Tour Supply today in Nashville. They came recommended by Mesa. The tech said that it sounded like the bias was off too. Good looking out man. Thanks

 

[twinky5959]

A friend of mine has this problem with his ac-30 and we think what might be happing is that there is a cap in line between the phase inverter and the plate for the tube. What this cap does is keep the dc voltage off the plate if these caps **** the bed, then boom, fireworks. Definately a bias issue. Hopefully this might help you or others with the same lightning show.

 

[dmt]

must be tesla tubes...

 

[stokes]

A friend of mine has this problem with his ac-30 and we think what might be happing is that there is a cap in line between the phase inverter and the plate for the tube. What this cap does is keep the dc voltage off the plate if these caps sh!t the bed, then boom, fireworks. Definately a bias issue. Hopefully this might help you or others with the same lightning show.

Thats a coupling cap,it feeds the ac signal to the power tube grid,and blocks dc voltage from the plate of the PI from reching the grid of the power tube.Not the other way around.If this cap leaks dc it will throw the bias of the power tube off.

 

[twinky5959]

Thank you for the correction. I'm rather new to the whole electronics side of amps. That could still be the cause right?