Unusual fault

[Rgeebee]

My fender  cvr guitar amp is dead on both channels until I give it a really strong input signal!
Then it works perfectly.
All tubes not microphonic when working.
I cleaned all the tubes pins but still the same problem.
Next time I use it same thing happens.
Any ideas?

[EL34]

You posted in the wrong board
Moving

[Rgeebee]

Sorry, new member

[PRR]

Stick a plug in/out the Effects loop many times, clean the contacts.

[Rgeebee]

This model doesn't have an effects loop.
Could this be a problem with the phase inverter tube?

[mresistor]

The first thing to do is try swapping tubes  - if you suspect it might be the PI then swap it out with a new/known good one. You should always have a couple of spare 12AX7 12AT7 tubes. Wouldn't have hurt to have gotten a spare 6L6/5881 duet before now due to the tube shortage.   Which are you using in the amp? and has the bias been checked? If your power tubes have drifted then the bias could need adjusting. It's also possible one of your power tubes has failed.

If you don't have another 12AT7 you could use one of the 12AX7s from one channel as the PI temporarily.


I think those PCB amps also have an Inrush Current Limiting Thermistor and I've read they can fail but I don't know what the symptoms are when that happens for sure - I suppose it would be low global voltages in the amp.

[mresistor]

Here's the schematic  And if one of the moderators or Doug could put it into the Fender schematics list that would be cool. 


https://www.thetubestore.com/lib/thetubestore/schematics/Fender/Fender-Custom-Vibrolux-Reverb-Reissue-Schematic.pdf

[tubeswell]

Are you certain it’s the amp? (And not guitar/guitar cable?)

[Rgeebee]

Thanks everybody, I could kick myself!
I thought it was an internal problem.
Turned out to be a break in the moulded speaker jack plug!
Replaced the plug and all fine now.
Amp is fantastic now.