Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: HelpMeRepair on June 30, 2025, 03:19:52 pm
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Hi guys !
I have a friend amp , 1st guitar amp recap , recap gone easy even wit that sandwiched board , but there something that I messed up along the way or I didn't pay attention (or it was like this before but he wont tell me ahha ! ) , well everything works except the reverb fonction !
When i turn the dial , its like a DC signal get into amplification :BangHead: , I'll put a link so you can hear it.
If someone can help , its some kind of a mess to probe around wit that kind of amp , I can't trace the signal when its all together and I dont have the proper bench , amp board older etc to do it so if any one have gone through the same kind of problem or have any idea from what part of the board / component that signal would go through, it would be a lot appreciated ! :worthy1:
(it may be the last time that I accept a friend ask me a recap job :laugh: on those kind of sandwich amp I can tell you ! he was kind of short on cash and wanted a favor and now I want to make it right! )
what I have tested so far and changed if was bad = big caps , 22uf caps , they are all good and on the right position , transistor , diodes, the IC , those little jumper that fail over manipulation and there joint .. everything circled in red in the picture.
here a video of what it sound like from my drives and what I have done so far : https://photos.app.goo.gl/Piw9gwaZTNY56kno7 , https://photos.app.goo.gl/CDE9jwwY3MQkvSCA8
Hope someone can help , thanks in advance !
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in the picture you show the 4558 reverb op amp holder but seemingly no IC(near the fourth pot)
Did you have it installed during your test?
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in the picture you show the 4558 reverb op amp holder but seemingly no IC(near the fourth pot)
Did you have it installed during your test?
I took a screenshot from a youtube video the board for the post ,yes the IC is installed dot on pin1
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you should post your amps pictures and schematics not someone else's....
How do you expect help otherwise???
Could that sound be the 12v relay that feeds the reverb be buzzing?
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you should post your amps pictures and schematics not someone else's....
How do you expect help otherwise???
Could that sound be the 12v relay that feeds the reverb be buzzing?
are you talking about the Omron G6A-274P-ST-US ? please explain why the relay would send a DC signal into amplification?
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here a schematic if you want to draw on it and repost etc
link : https://photos.app.goo.gl/1KFpRkWM8TDxTeXB8
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That's not a schematic but a Layout. Have you got the schematic?
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hehe you are totally right , just found one !
link : https://photos.app.goo.gl/4SpfUE87YaJvhAmF7
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You need to go through the schematic and check DC voltages at the test points, especially in the low voltage supply and reverb circuit.
If you replaced all the diodes, and all the electrolytics, maybe something was installed backwards. Or, maybe there was a part that was faulty which wasn't replaced.
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You need to go through the schematic and check DC voltages at the test points, especially in the low voltage supply and reverb circuit.
If you replaced all the diodes, and all the electrolytics, maybe something was installed backwards. Or, maybe there was a part that was faulty which wasn't replaced.
yes I'll continue tomorow , I'll take it apart again and look for some faulty resistor or caps even broken trace on the reverb circuit
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so you tried subbing in another 4558 (or TLO72 )?
Also those C30 boards are crap to maintain. Too thin, traces and pads crack all the time, If you've been careless with component unsoldering and removal, you might have created all sorts of issues. And those little solid wire interboard jumpers are prone to cracking when you yank the boards in an out. And the ribbon cable...
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yes I'll continue tomorow , I'll take it apart again and look for some faulty resistor or caps even broken trace on the reverb circuit
Right. Test the components. Also, in the schematic you shared, there's test points. If the voltages at those test points don't align with the schematic, then it could help isolate your problem...even if it is a bad trace, etc...
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so you tried subbing in another 4558 (or TLO72 )?
Also those C30 boards are crap to maintain. Too thin, traces and pads crack all the time, If you've been careless with component unsoldering and removal, you might have created all sorts of issues. And those little solid wire interboard jumpers are prone to cracking when you yank the boards in an out. And the ribbon cable...
yes I did ! even tried 2 different 4558 , always looking for bad joint / trace / jumpers when I manipulate the board.. , yup many flaws on that board , must have been cheap to produce !