Channel Four on my roadsters volume keeps fading in and out

[label thief]

i swapped out all the tubes(power and pre).. still have the same problem.. on channel four when i'll play something on say.. the higher strings it starts fading in and out as if someone was pushing down on a volume pedal. tried switching to diodes.. tried another guitar.. tried without any pedals. still nothing. any ideas?

 

[pokerrules47]

Search the threads on this board, there is a fix... search for roadster cathode follower

 

[label thief]

interesting. my question is why would i need to put chinese tubes in v3 and v5 if any other tube worked in the past?
but anyway, can someone link me to a solid tube i can put in these slots to have no problems?

 

[domct203]

interesting. my question is why would i need to put chinese tubes in v3 and v5 if any other tube worked in the past?
but anyway, can someone link me to a solid tube i can put in these slots to have no problems?

Exactly what tubes were in those positions in the past?

Shuguang 9th Generation (chinese), JJ ECC83, or just about any NOS tube will be fine in a cathode follower. The current Mesa Russian 12AX7 is a JJ, and holds up in these spots.

I had the Mesa Russian-2 (Electro-Harmonix) and Mesa Russian-1 (Sovtek) both fail in the cathode follower positions.

This may not even be the issue with your amp. We're all just troubleshooting right now.

Dom

 

[label thief]

at first i had 6 JJ ECC83S's one of them being balanced for the phase inverter in V6... the amp worked fine. then one day it just started happening so i switched to:

- V1 Tungsol 12AX7
- V2 High Gain JJECC83
- V3 Penta 12AX7
- V4 Penta 12AX7
- V5 Shuguang 12AX7 9th gen
- V6 Sovtek LP/LPS

 

[domct203]

Does this happen on any other channels? Does it happen with different guitars/guitar cable? Does it happen with the FX Loop hard-bypassed? Are you troubleshooting with just guitar -> cable -> amp?

Dom

 

[label thief]

yes to all your questions :?

 

[domct203]

Well it sounds like you've covered all the bases. Looks like the next step would be a call to Mesa.

Dom

 

[domct203]

One more thing I just thought of....

Even when you switch to diodes I believe that the 5U4GB tubes are still in the circuit. Switch the amp to diode rectification and remove the 5U4GB rectifier tubes and see if the problem persists. If not, replace the rectifier tubes.

Good luck.

Dom

 

[label thief]

im not really familiar with tubes. have i had chinese tubes in those slots that need it?

 

[domct203]

Yes, both the Shuguang and Penta are chinese (they are actually made in the same factory).

The JJ ECC83 is what Mesa is using now and has no problems in cathode follower positions.

Dom

 

[Authorized Boogie]

Hey LabelTheif -

Have you NOT had any problems on Ch 3 or do you use Ch 3?

If you have the issue on both Ch 3 AND Ch 4 then this would lean toward the possibility of the problem being cathode follower related. If not tube related and the problem continues, it could be time for a tech to take a look.

Some of the more recently produced Russian preamp tubes (within the last 5 years or so) don't hold up reliably in cathode follower positions in the preamp. They worked fine for years but something changed and was a cause for us to switch our supply for 12AX7s and we have had essentially no cathode follower pre tube failures.

Look forward to your reply.

A-Boogie

 

[MBMusicMan]

Quick bit of thread robbery, but boogie joins the boogie board? Awesome!