I did a full Ecap replacement on a '68-'69 dripedge Bassman. It is an AC568 circuit although the tube chart is stamped AB165. I added a bias adjustment trimpot to the balance pot. I left the circuit stock.
My voltages seem to be running correctly. All new tubes installed. The issue I am having is extreme microphonics in V3. A loud ping when tapping the tube and chassis. Much more than normal. Changing the tube does not help. I do not get any crackling noise on the board such as a bad solder joint would cause.
I am running out of ideas on the cause.
Can anyone give me some help?
Fender Bassman microphonic issue!
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WhopperPlate
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Re: Fender Bassman microphonic issue!
How many tubes did you swap in? Brand new ? Helps to get them ordered tested for microphonics and noise. Wouldn’t be the first time a new tube was pinging out the gate.
What brand tubes? Fwiw I have found tungsols to be very prone to microphonics, also sensitive to parasitic oscillations . Always have much better luck with JJ
Sometimes a wire resring against the chassis can be very microphonic, especially pvc solid core , but I usually find thats the case in long leads in higher gain circuits. Trainwreck comes to mind.
Once I discovered a faulty potentiometer that was microphonic believe it or not
What brand of caps did you use? I have found similarly microphonic and parasitic oscillation sensitivity with F&T caps.
Might not be any one thing , and a perfect storm of components, but who knows until you sort it out.
Hope this gives you some food for thought
What brand tubes? Fwiw I have found tungsols to be very prone to microphonics, also sensitive to parasitic oscillations . Always have much better luck with JJ
Sometimes a wire resring against the chassis can be very microphonic, especially pvc solid core , but I usually find thats the case in long leads in higher gain circuits. Trainwreck comes to mind.
Once I discovered a faulty potentiometer that was microphonic believe it or not
What brand of caps did you use? I have found similarly microphonic and parasitic oscillation sensitivity with F&T caps.
Might not be any one thing , and a perfect storm of components, but who knows until you sort it out.
Hope this gives you some food for thought
Charlie
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Stevem
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Re: Fender Bassman microphonic issue!
I have had my share of new tubes that were microphonic, so as posted above you should review that possibility.
Also if you pass enough gain thru even a new Disc type cap you can talk into them as if they where a microphone.
Any original caps like these should be suspect of creating the issue you have.
In any Fender the first thing I do just for the sake of tone no less microphonics is to replace that cheap PI input cap with a orange drop type.
Also if you pass enough gain thru even a new Disc type cap you can talk into them as if they where a microphone.
Any original caps like these should be suspect of creating the issue you have.
In any Fender the first thing I do just for the sake of tone no less microphonics is to replace that cheap PI input cap with a orange drop type.
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Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Re: Fender Bassman microphonic issue!
Well, I did put a new JJ in V3 and it is significantly quieter than any of the new Mullard tubes. Go figure.
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WhopperPlate
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