V4....what about the 5th tube?????

[Pat]

Hi all,
Noob here, so I want to replace the ecc81 in v4 to see if it fixes the reverb problem, can anyone tell me what the 5th tube is for???? It's in a studio 22+, the reverb works fine untill I bump the amp, the reverb rattles and is replaced with noise instead of reverb.
Any feedback on this would be appreciated.
thanks
Pat

 

[RussB]

The "5th tube" is the phase inverter (PI). It should be a 12AX7/ECC83

Check the connections to the reverb tank. The reverb driver is V4

 

[MusicManJP6]

Yea check the reverb tube, and then try a known good tube in PI slot. It should be a balanced tube for best results.

 

[RussB]

It should be a balanced tube for best results.

False. A balanced tube in in the PI of a guitar amp is rather silly because the circuit is designed to be UNbalanced!

Balanced PI tubes are for audiophile amplifiers, and don't do anything for guitar amps

 

[bancika]

Balanced PI tubes are for audiophile amplifiers, and don't do anything for guitar amps

+1 asymmetrical clipping can be interesting for guitar

 

[Pat]

thanks for your replies, I found the problem was not the V4 tube at all but the springs inside the tank were not balanced? ie. the four little springs that hold the main springs were not set at even height.
thanks again though

 

[RussB]

thanks for your replies, I found the problem was not the V4 tube at all but the springs inside the tank were not balanced? ie. the four little springs that hold the main springs were not set at even height.
thanks again though

Not sure I follow, but I'm guessing you're way off on the diagnosis. Do you have a DMM?

 

[bigbean]

UNeeda new reverb pan.

20 some year old units require repair and update. You will probably find your problem will return and be intermittent. When it does, yank the old pan and replace with correct unit from mojotone or some other supplier. If your not sure which unit you need ax em. Equals a "half a tank of gas" repair that can be safely done by anyone who can operate a screw driver. I wouldn't try to "improve" the reverb by putting an incorrect reverb pan that's "better".

You might check some alt placements for the pan - (might need longer cables) - a few inches can lower the hum in the circuit.

http://www.schematicx.com/schematic/mesa-boogie-studio-22-caliber-plus-schematic/



best of luck