Hello everyone... I need some help from more experienced amp techs on this forum. A friend of mine asked me to help him with his Twin Amp that developed not so loud but annoying ghost sounds that are more pronounced on the lower notes and sounds like a hum but an octave or two lower. I recorded the video demoing it and posted it on Youtube:
https://youtu.be/a6P1FvWVvng?si=WM0Ds7j1VAj89Wgg
I tested all the tubes on my vintage tube tester - they seem to be ok. I also replaced all my preamp tubes (one at a time) with a one good tube - did not help. All the filtering caps were replaced with the decent ones a year ago (I will try to attach photos). Does anyone know what else can be causing these ghost notes?
Thank you for your time, help and knowledge,
Alex.
Ghost sound problem on 70's Tween Reverb
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Ghost sound problem on 70's Tween Reverb
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Stevem
- Posts: 5144
- Joined: Fri Jan 24, 2014 3:01 pm
- Location: 1/3rd the way out one of the arms of the Milkyway.
Re: Ghost sound problem on 70's Tween Reverb
I would start by ohm checking all the ground paths by looking for a high resistance.
Just because the amp might’ve been recapped even just 3 months ago does not mean that one can not be going bad, so if all the ground paths check out then I would jump out the filters one at a time.
If this issue is due to an oscillation condition then you might be able to narrow it down to a section of the amp.
Pull the audio signal off of the reverb send jack and pump that into another amp, or even a 8 ohm speaker to listen to it.
Yes, that reverb send is actually a 1 watt amp that was made to drive a 8 ohm load.
You did not say what year twin this is, but I recall models with a master volume also had a line out jack I think .
If so run that into another amp to see if the issue is also heard there.
Just because the amp might’ve been recapped even just 3 months ago does not mean that one can not be going bad, so if all the ground paths check out then I would jump out the filters one at a time.
If this issue is due to an oscillation condition then you might be able to narrow it down to a section of the amp.
Pull the audio signal off of the reverb send jack and pump that into another amp, or even a 8 ohm speaker to listen to it.
Yes, that reverb send is actually a 1 watt amp that was made to drive a 8 ohm load.
You did not say what year twin this is, but I recall models with a master volume also had a line out jack I think .
If so run that into another amp to see if the issue is also heard there.
When I die, I want to go like my Grandfather did, peacefully in his sleep.
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!
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!
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Stevem
- Posts: 5144
- Joined: Fri Jan 24, 2014 3:01 pm
- Location: 1/3rd the way out one of the arms of the Milkyway.
Re: Ghost sound problem on 70's Tween Reverb
I would start by ohm checking all the ground paths by looking for a high resistance.
Just because the amp might’ve been recapped even just 3 months ago does not mean that one can not be going bad, so if all the ground paths check out then I would jump out the filters one at a time.
If this issue is due to an oscillation condition then you might be able to narrow it down to a section of the amp.
Pull the audio signal off of the reverb send jack and pump that into another amp, or even a 8 ohm speaker to listen to it.
Yes, that reverb send is actually a 1 watt amp that was made to drive a 8 ohm load.
You did not say what year twin this is, but I recall models with a master volume also had a line out jack I think .
If so run that into another amp to see if the issue is also heard there.
Also try unplugging the reverb pan totally to see if that changes anything.
Just because the amp might’ve been recapped even just 3 months ago does not mean that one can not be going bad, so if all the ground paths check out then I would jump out the filters one at a time.
If this issue is due to an oscillation condition then you might be able to narrow it down to a section of the amp.
Pull the audio signal off of the reverb send jack and pump that into another amp, or even a 8 ohm speaker to listen to it.
Yes, that reverb send is actually a 1 watt amp that was made to drive a 8 ohm load.
You did not say what year twin this is, but I recall models with a master volume also had a line out jack I think .
If so run that into another amp to see if the issue is also heard there.
Also try unplugging the reverb pan totally to see if that changes anything.
When I die, I want to go like my Grandfather did, peacefully in his sleep.
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!
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: Ghost sound problem on 70's Tween Reverb
Thank you for very detailed response. I will be back to work tomorrow and will check all these suggestions.. I have been building and preparing amps since 2008, on and off , and, maybe, I have had this type of problem, but I forgot all about it and forgot what causes it, so the help of all those people whose memory is still fresh, very much appreciated 
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BrownIsound
- Posts: 69
- Joined: Sat Apr 23, 2022 9:39 pm
Re: Ghost sound problem on 70's Tween Reverb
Yes, I would also suggest checking the filter caps, sounds like ghosting.