Blackface Vibrolux

Grubey Doo · 12-04-2006, 03:08 AM

I got one of these on the bench. I tried everything. It kills the output tube closest to the rectifier. I disconnected the .1 caps that feed the grids, injected a signal into the lifted ends of each cap and the side that has the problem the signal is louder than the ok side.
The grid resistors are right on also so I dunno, any ideas?

stokes · 12-04-2006, 03:15 AM

Is the bias voltage okay?Did you check to see if the caps are leaking excessive dc voltage to the grids?

Amp Kat · 12-04-2006, 07:31 PM

I've seen one of the 100k plate resistors of the PI on either side open up causing the signal on that side to drop way down.

stokes · 12-05-2006, 03:43 AM

Dont think losing the signal at the input would cause the tube to fry.Also dont think putting a signal into one side of a push pull out put is a very definitive test for a power tube failure.More likely you are losing bias voltage to that tube.Also if the input cap is leaking a lot of dc it would change the bias of that tube.

12-04-2006, 03:08 AM	#1
Grubey Doo Junior Member Join Date: Dec 2006 Posts: 9	Blackface Vibrolux I got one of these on the bench. I tried everything. It kills the output tube closest to the rectifier. I disconnected the .1 caps that feed the grids, injected a signal into the lifted ends of each cap and the side that has the problem the signal is louder than the ok side. The grid resistors are right on also so I dunno, any ideas?

12-04-2006, 07:31 PM	#3
Amp Kat Senior Member Join Date: Jul 2006 Location: Baton Rouge,LA Posts: 1,062	I've seen one of the 100k plate resistors of the PI on either side open up causing the signal on that side to drop way down. __________________ KB

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12-04-2006, 03:15 AM	#2
stokes Old Timer Join Date: May 2006 Location: NYC Posts: 1,305	Is the bias voltage okay?Did you check to see if the caps are leaking excessive dc voltage to the grids?

12-05-2006, 03:43 AM	#4
stokes Old Timer Join Date: May 2006 Location: NYC Posts: 1,305	Dont think losing the signal at the input would cause the tube to fry.Also dont think putting a signal into one side of a push pull out put is a very definitive test for a power tube failure.More likely you are losing bias voltage to that tube.Also if the input cap is leaking a lot of dc it would change the bias of that tube.

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