Williamson tube amp. Noise at turn off.

[Gold70]

Quote from gadget73:
"Square wave testing can also indicate potential stability issues. Sharp overshoot on the rising edge with ripples (ringing) along the top often indicate a high frequency resonance. This is mostly something you deal with on tube amps with global feedback, but it indicates the possibility of the amp oscillating and maybe nuking a tweeter or other undesirable behavior."

I just read the above comment and wondering if it relates my problem. "nuking a tweeter" scares me as the "noise" comes from a beryllium mid-range driver.
I will get the adjustable cap back in order first before doing anything else to the amp. Thanks everyone for being so helpful!

 

[zackthedog]

It's unlikely that the amp will go into the sort of violent or prolonged oscillation that used to kill tweeters, especially an amp as well-built as that. But it's best not to use it until you identify the problem.

 

[gadget73]

The adjustable cap would mostly only affect high frequency stuff. Wouldn't cause motorboating at power off. Thats low frequency stability stuff. Might produce some extra sizzle or harshness in the tweeter though if its on the ragged edge of hf instability.

Really would be awesome if a schematic for this thing existed or could be created. Would answer a lot of questions.

 

[Gold70]

I found someone who has an oscilloscope. Hope he can get the adjustable cap back and will see what else he could do about it...Thank you, everyone! I will report back.

 

[Gold70]

This is what I got: He checked all the capacitors and said all seem in very good order except one of 5 "tall" canned capacitor that reads not as good on Oscilloscope. He is going to add another capacitor to that "not perfect" cap as a "parallel" ?
The noise at the power down. He does not seem to be so concerned. He said most of modern amp has a relay built in place that cut off the power from the amp to speaker at power down and he is going add one onto the amp by the speaker terminals on the amp.

Are all of this making sense?
He is an older gentle man who worked as an electronic engineer designing circuit board for LG electronic company.
By the way, he is in awe what he saw about the amp.

 

[zackthedog]

This is what I got: He checked all the capacitors and said all seem in very good order except one of 5 "tall" canned capacitor that reads not as good on Oscilloscope. He is going to add another capacitor to that "not perfect" cap as a "parallel" ?
The noise at the power down. He does not seem to be so concerned. He said most of modern amp has a relay built in place that cut off the power from the amp to speaker at power down and he is going add one onto the amp by the speaker terminals on the amp.

Are all of this making sense?
He is an older gentle man who worked as an electronic engineer designing circuit board for LG electronic company.
By the way, he is in awe what he saw about the amp.

Sounds reasonable. My only suggestion is that he bypass or remove the weak cap entirely and substitute something suitable in its place. Might be better for the long-term health of the amp. While he's at it he might also make sure those adjustable capacitors are set properly. His scope should tell him that. ;-)

 

[Gold70]

Sounds reasonable. My only suggestion is that he bypass or remove the weak cap entirely and substitute something suitable in its place. Might be better for the long-term health of the amp. While he's at it he might also make sure those adjustable capacitors are set properly. His scope should tell him that. ;-)

I got the amp home tonight and saw new parts in it. Gee! he is so rough on the amp. The relay was hot-glued to the chassis and the makeshift wires? and guess what the same noise is still there, the same loudness, same problem. He barely speaks English and I could not understand the things he said he did to the amp. I am sitting here feeling lost. And there is an obvious "humming" on the bad channel that was not there before.

 

[Selmerdave]

Oh wow, that's not what you want to happen. Obviously the amp should not have new problems when you get it back. I would have thought there's a member here in the Toronto area that could help you out. The tech should certainly correct the issues, but maybe you're not confident in him making matters worse. I'm not able to look at the pictures at the moment but perhaps someone can spot something, but sorry to hear you're going through this. At some point in the end, you will have a beautiful sounding amp.

 

[zackthedog]

I got the amp home tonight and saw new parts in it. Gee! he is so rough on the amp. The relay was hot-glued to the chassis and the makeshift wires? and guess what the same noise is still there, the same loudness, same problem. He barely speaks English and I could not understand the things he said he did to the amp. I am sitting here feeling lost. And there is an obvious "humming" on the bad channel that was not there before.

Oh hell, that's not right. I'm so sorry. But it CAN be corrected. This is not a terribly complicated amp, it's a Williamson with tone controls added. I wish I were closer, I might be able to help, but it's a long drive from Southern Oregon. ;-( I would echo Selmerdave's comment. Perhaps post a new thread asking if any experienced AKers in the Toronto/Upstate NY area could help, or suggest a better tech. The upside is that you have lots of documentation of the original configuration.

 

[Gold70]

Oh wow, that's not what you want to happen. Obviously the amp should not have new problems when you get it back. I would have thought there's a member here in the Toronto area that could help you out. The tech should certainly correct the issues, but maybe you're not confident in him making matters worse. I'm not able to look at the pictures at the moment but perhaps someone can spot something, but sorry to hear you're going through this. At some point in the end, you will have a beautiful sounding amp

 

[Gold70]

Oh hell, that's not right. I'm so sorry. But it CAN be corrected. This is not a terribly complicated amp, it's a Williamson with tone controls added. I wish I were closer, I might be able to help, but it's a long drive from Southern Oregon. ;-( I would echo Selmerdave's comment. Perhaps post a new thread asking if any experienced AKers in the Toronto/Upstate NY area could help, or suggest a better tech. The upside is that you have lots of documentation of the original configuration.

Thank you Zackthedog and Selmerdave for your kind words. I need to slow down about this