Feedback Problem

[BigMac5]

Friday and Saturday my Roadster started having insane amounts of feedback in Channel 4 modern. I never had a problem with the amp before. I tried three different guitars but the feedback remain on that channel only. I think one of the pre-amp tubes is microphonic, but which one?

 

[stephen sawall]

Go look at the manual it well be in there. You can always just do one at a time till you find the one. you can also take pencil or something and tap the tubes well the amp is on the one that goes pop or rings is the one probably .

Page 22 in the manual ....

http://www.mesaboogie.com/manuals/Roadster.pdf

 

[BigMac5]

I already looked at the manual before I posted. It only says the following:

"The best way to approach a pre-amp tube problem is to see if it occurs only in one specific mode or channel. This should lead you to the tube needing replacement. Then all that remains is to swap the suspect tube for a known good performer."

 

[dodger916]

I already looked at the manual before I posted. It only says the following:

"The best way to approach a pre-amp tube problem is to see if it occurs only in one specific mode or channel. This should lead you to the tube needing replacement. Then all that remains is to swap the suspect tube for a known good performer."

I see they reference a "Tube Task Chart" on page 23 of the manual, but I don't see where the manual includes one!

 

[BigMac5]

I looked at the manual for the Dual Rectifier and it includes a "Tube Task Chart" but it only has 5 preamp tubes not 6 like the Roadster.

I also looked at the Roadking manual and it includes a "Tube Task Chart" with 6 preamp tubes.

This is what it says on page 43:

http://www.mesaboogie.com/manuals/RoadKing2_v2.pdf

V1 A-First Gain Stage
V1 B-Second Gain Stage
V2 A-3rd Gain Stage-Ch 1 & 2
V2 B-3rd Gain Stage- Ch 3 & 4
V3 A-4th Gain Stage- Ch 3 & 4
V3 B-Tone Stack Driver Ch 3 & 4
V4 A/B-Reverb Return/Reverb Driver
V5 A/B-FX Loop Send/FX Loop Return
V6 A/B-Phase Inverter/Driver

From this, my suspect bad preamp tube is V3. If that doesn't fix it then I'll try V2.

 

[dodger916]

seems logical.