Herbert Channel 3 oscillation problem?

  • Thread starter Thread starter LPJCHAMP
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LPJCHAMP

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Hello everyone! I am new to the forum, but I have had my Herbert for 4 or 5 years now. I can't even remember, it is my main amp of course. It has always been very solid for me and I have no complaints, but this year it developed a strange issue in Channel 3. When I switch to this channel, a strange sound comes through the speakers, and as I adjust the gain knob on the amplifier, the frequency of the sound changes. I thought it might have something to do with tubes, so I had taken it into my tech and put winged C el34's and TAD 7025s' in it, and asked him to check out the issue in channel 3. He is a pretty good tech, but the tubes did not solve the problem and he could not get to the bottom of what was causing the issue. He called the problem an "oscillation in the channel 3 tone circuit with no apparent cause." The rest of the amp runs smoothly, the strange frequency oscillation sound only occurs on channel 3 when there is no guitar being played though it. Does anyone know what needs to be done to solve this? Any help is much appreciated :) - Justin :doh: :)
 
Hello Justin,

is it a high pitch squealing noise? Does this noise stop when you lower the gain of ch3 to a certain point?

It sounds to me like 1 or 1 broken capacitor that need to be replaced.

Important: please let me know what knobs you can turn to make the noise go away and reappear.

Kind regards,

Jens Kruse
 
Thank you Jens for the quick response! I am away from my place for the next week so I will check the specifics of what the knobs are doing when I get home next week and post what I find. From what I have already experimented with and remember, I can say it is a hard type of sound to explain. It is like a solid pitch hum squeal sort of thing. I turned all the channel controls down to 0 and adjusted the gain knob and it just seems to change the pitch of the sound. I can only describe it like something I hear out of a synth in techno when they adjust the filter things that make the pitch go up and down . That is what my ch. 3 gain knob is doing.
 
As soon as you are able, please take a photo of your amp's circuit board (jacked up upside down) and email it to me. I will mark 2 capacitors and 1 resistor to replace and that might be all for your tech to do.

Jens
 
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