power supply failure?

EETStudent · 01-14-2008, 09:24 PM

Wasnt getting any sound out of the amp. Checked the B+ and measured 15VDC. Obviously way too low. The incoming AC source was 120V however. Does this mean my PT is toast? I did push the voltage pretty high. Suppose that was a mistake.

Twist · 01-15-2008, 12:18 AM

What amp are you working on?

EETStudent · 01-15-2008, 01:12 AM

It's an old Rauland tube PA head. No schematic though. Two EL34s, unknown power and output transformers. Been experimenting with different preamps.

Don Moose · 01-15-2008, 01:53 AM

How's the voltage with no rectifiers or filters? (It'd be AC, obviously)

It could be too much load to actually support, but somehow doesn't kill the PT.
(not likely, but worth a try)

Enzo · 01-15-2008, 01:56 AM

OK, you can do this.

What is between the power transformer and the B+? There is a secondary winding, so what level AC is across it? There are rectifiers, so is that AC getting to them? Is there any DC coming out of them? SOmewhere in there is a standby switch, so does it work? I mean when ON is there very low resistance across it? Is the filter cap charging up? WHERE did you measure that 15v B+? At a tube? At a filter? Where?

If there is no HV AC at the secondary, an disconnecting the secondary from the circuit makes no change, then I would suspect the PT. But not until I checked the whole deal.

EETStudent · 01-15-2008, 07:16 PM

Enzo and Don, thanks for you guys input. Went through some checks like you both mentioned, turns out the fuse had blown. Replaced it and its up and going again. This is can live with. I now know more about troubleshooting this sort of problem thanks to your advice.

01-14-2008, 09:24 PM	#1
EETStudent Senior Member Join Date: Nov 2007 Location: Columbia, SC Posts: 342	power supply failure? Wasnt getting any sound out of the amp. Checked the B+ and measured 15VDC. Obviously way too low. The incoming AC source was 120V however. Does this mean my PT is toast? I did push the voltage pretty high. Suppose that was a mistake.

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01-15-2008, 12:18 AM	#2
Twist Senior Member Join Date: Nov 2007 Location: Springdale, Arkansas Posts: 273	What amp are you working on?

01-15-2008, 01:12 AM	#3
EETStudent Senior Member Join Date: Nov 2007 Location: Columbia, SC Posts: 342	It's an old Rauland tube PA head. No schematic though. Two EL34s, unknown power and output transformers. Been experimenting with different preamps.

01-15-2008, 01:53 AM	#4
Don Moose Senior Member Join Date: Jul 2007 Location: Indianapolis Posts: 676	How's the voltage with no rectifiers or filters? (It'd be AC, obviously) It could be too much load to actually support, but somehow doesn't kill the PT. (not likely, but worth a try)

01-15-2008, 01:56 AM	#5
Enzo Senior Member Join Date: May 2006 Location: Lansing, Michigan, USA Posts: 10,366	OK, you can do this. What is between the power transformer and the B+? There is a secondary winding, so what level AC is across it? There are rectifiers, so is that AC getting to them? Is there any DC coming out of them? SOmewhere in there is a standby switch, so does it work? I mean when ON is there very low resistance across it? Is the filter cap charging up? WHERE did you measure that 15v B+? At a tube? At a filter? Where? If there is no HV AC at the secondary, an disconnecting the secondary from the circuit makes no change, then I would suspect the PT. But not until I checked the whole deal.

01-15-2008, 07:16 PM	#6
EETStudent Senior Member Join Date: Nov 2007 Location: Columbia, SC Posts: 342	Enzo and Don, thanks for you guys input. Went through some checks like you both mentioned, turns out the fuse had blown. Replaced it and its up and going again. This is can live with. I now know more about troubleshooting this sort of problem thanks to your advice.

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