Roadster (Combo) Effects Loop Issue

[diesel389]

Hey Y'alls-
Hoping someone can help me with this issue. I'm having a significant drop in output on channel 2 with my effects loop engaged (probably about 30-40% loss) and slight loss of output in channel 3 and 4 too. I've checked every pedal cable and possible weak link in my pedal chain and everything checked out okay. Any ideas on what may be causing this issue?

Thanks for any feedback.

CHeers

jp

 

[bendo]

1st, maybe a stupid question, but, you've adjusted the send level via the knob in the rear?

If so, replace the V5 tube with a known good 12ax7.

 

[diesel389]

Yes, I keep the FX level at noon as Mesa recommends....Why would it be V5 preamp tube? Also, is there a test you can do by flicking them to see if they're still good?

 

[bendo]

Yes, I keep the FX level at noon as Mesa recommends....Why would it be V5 preamp tube? Also, is there a test you can do by flicking them to see if they're still good?

Because V5 controls the FX loop. A weak tube can loose volume.

You could also try turning the send level up. Noon is only a starting point. The recommend to start with all controls at noon and adjust to taste from there.

 

[diesel389]

thanks for your reply, I'll get a new tube

cheers,

jp

 

[diesel389]

I actually went back and checked out my tubes and noticed that 2 of the caps on the preamp tubes were partially coming off. I retested the effects loop and everything works perfect now!

What's the purpose of the tube caps? can I just leave them off?

Thanks again for your help

jp

 

[bendo]

To block EMI (Electro Magnetic Interference). Additionally, on combos where the tubes hang upside down, to keep them from working loose and falling out.