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Mesa Dual Rectifier/Trem O Verb

4/22/2005 10:35 AM
Mesa Dual Rectifier/Trem O Verb
My Trem O Verb has an issue where the sound comes and goes.It is on the red channel only.It has no crackling or popping sound like a bad joint .When playing the sound just comes and goes at short intervals.I can see nothing physically wrong with any of the parts and have tested most of the reistors and diodes in the red channel and things look OK.  
I do fine working on my Fenders and Marshalls but the Mesa is a bit over my head so any help is appreciated.  
What are the rectangular,black components that are stacked?Could this be one of the relays?
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4/22/2005 12:33 PM
Tom Phillips

"What are the rectangular,black components that are stacked?Could this be one of the relays?"
Those are analog optoisolators used in the extensive Dual Rectifier/Trem O Verb switching matrix. The trade name is "Vactrol". There are about 25 of them in the circuit and the stacked mounting makes them a real pain to work on. There are also 2 or 3 electro-mechanical relays on the board. They are larger rectangle packages.  
4/22/2005 7:23 PM

Thanks for your reply Tom.I am familiar with the relays but did not know what the opto's were for other than being in the switching matrix.  
Any idea what may be causing my problem?How would you test these opto's or where can I find more info on them?  
4/23/2005 12:30 PM
Tom Phillips

I believe that the type of Vactrol used in the MesaBoogie Dual Rectifier Trem-O-Verb is the VTL5C9. You can find a data sheet at  
However, I don’t know if a Vactrol will be the cause of your “…the sound just comes and goes at short intervals” problem. Intermittent problems are a pain. If you can catch the amp doing the problem on the bench then you can signal trace and start to isolate the problem. If the signal stops at a Vactrol it could be internal to the Vactrol or a problem with the supply voltage / switching matrix that turns the Vactrol on and off. Sounds like you already know that the problem is in the red channel pre-amp but I’d still check that the power amp is working when you loose signal by injecting a signal into the FX return jack. Also make sure the power supply voltages are OK during the fault condition. Start with the easy stuff like swapping out tubes. I have found tubes that turned off when they lost heater power due to a bad solder joint or bad tube socket. That caused a problem similar to what you have described. Sorry I can’t point you to a specific problem. Troubleshooting the dense PCB layout in a MB is challenging.  
Good Luck,  
4/23/2005 4:10 PM

You've been very helpful and I appreciate your time.  
I'll let you know what I find out.

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