P-Zero Problems: help needed

[RochaCullen]

Hey All,

The other day one of my AN P-Zero monos developed a loud buzz. First thing I did was open it up and check the valves, one of them looked a bit cloudier than the other, but when I swapped both the power valves into the other functioning mono block they worked fine. So my first thought was that its not the valves, which I was hoping for as that would be a quick fix.

So next I opened up the case fully:

http://i830.photobucket.com/albums/zz230/rochaCullen/P-Zero%20internals/2_1_2014412.jpg

http://i830.photobucket.com/albums/zz230/rochaCullen/P-Zero%20internals/2_1_2014409.jpg

Everything looked in good order, and there were no obvious signs of problems. Hhhhmmmmmm

Then I looked at the back of the PCB:

http://i830.photobucket.com/albums/zz230/rochaCullen/P-Zero%20internals/2_1_2014414.jpg

And a close up:

http://i830.photobucket.com/albums/zz230/rochaCullen/P-Zero%20internals/2_1_2014416.jpg

Now I'm not an expert on valve amps, but that looks to me like it might be a bit of a problem.

So I suppose the valid questions are:

1 - was that caused by a malfunctioning valve?
2 - is it repairable?
3 - and if so how?

I would imagine the valve seat needs to be resoldered and then the offending valve replaced?

Any help would be appreciated. I love my P-Zeros as they work fantastically well with my Celestion Ditton 44s, and I really want to get these back up and running. :(

Thanks in advance,

Nathan

[RochaCullen]

Well I've resoldered that dirty mess and the problem remains. Seems I'll have to enlist some professional help.

[JimC]

Is there Audio audible below the Buzz?

It could be many things.......
It could be an 'earthing' problem causing a buzz to be added to the signal. However looking at the picture of the Valve Socket I suspect this is not the case.
It could be a Smoothing Capacitor failed but this would have affected both Valves so again, not likely.
It could be a fault with the Output Transformer. It could be some incorrect D.C. at the input (grid) of the Valve. It could be a failure of the Cathode Resistor and Capacitor (if fitted).

Do you have a Meter and a Circuit and are happy to have a go yourself? I don't mean to sound disrespectfull but you are aware that there is lethal amounts of Voltages in a Valve Amp? If you are and have access to some test equipment and a circuit you could post some measurements and we may be able to deduce what's gone wrong.

James.

[RochaCullen]

Is there Audio audible below the Buzz?

It could be many things.......
It could be an 'earthing' problem causing a buzz to be added to the signal. However looking at the picture of the Valve Socket I suspect this is not the case.
It could be a Smoothing Capacitor failed but this would have affected both Valves so again, not likely.
It could be a fault with the Output Transformer. It could be some incorrect D.C. at the input (grid) of the Valve. It could be a failure of the Cathode Resistor and Capacitor (if fitted).

Do you have a Meter and a Circuit and are happy to have a go yourself? I don't mean to sound disrespectfull but you are aware that there is lethal amounts of Voltages in a Valve Amp? If you are and have access to some test equipment and a circuit you could post some measurements and we may be able to deduce what's gone wrong.

James.

Hey James,

There is audio audible beneath the buzz. And like you've pointed out it could be a number of things causing this issue, and while I have a meter and am careful enough not to get fried, I am more than happy to admit when I've hit the limit of my tinkering ability :), so I think I'll have to defer to someone who is in the trade who might be able to help me.