Mesa Roadster Chan 3 no sound....Voodoo Platinum Modded

T

TysC

New member
Hey guys, i'm quite literate when it comes to guitar amps for starters. So ANY advice is much appreciated.

I have sent Trace emails but I have not gotten a response so i'm trying to find out whats happening.....


Channels 1, 2 and 4 work perfectly fine.

Channel 3 however one day just decided to considerably/massively drop in volume, it's ever so faintly still there, but I was wondering if anyone could help. I haven't opened up the amp yet as it has the Voodoo Amps Platinum Mod and i don't really want to go poking around in there until I may have a better idea. Ofcourse i doubt it is a 'preamp' tube problem as channels 3 & 4 i'm sure are identical (almost) and both use exact gain stages etc. I've fiddled with the knobs and tried wiggling them incase there was a ground problem but nothing, and turned the channels dials all the way up and down. But nothing, it's strange, it just stopped working, i didn't move the amp head or anything.

Please let me know if anyone has any suspicions!!!

Appreciate everyones time,

Tys
 
Hi Tysc,
If the amp is fine in most of the channels, and you had noticed a volume drop in the channel that is not working, it could most likely just be a pre amp tube for that channels input or gain stage. A pre amp tube has two sides to it so it can be used to do an input for say gain stage 2 and the input for stage 3.

Your manual doesn't give a tube breakdown like the others do, so you'll have to search. Most issues like that are caused by tubes, and the key here is, you noticed a drop in volume before it stopped working altogether.


Bill
 
Hi Bill,

Thanks for the reply, but I have successfully modded quite a lot of amps/pedals myself so i'm well past the "try a preamp tube" idea. I just haven't opened it up yet to inspect.

The manual actually does give a tube breakdown, channels 3 & 4 use the same gain stages.

I'm not sure what type of recto's your using, but the Roadster is what i have in question.

Cheers,
 
Hey Tysc,
No problem. Hope you didn't think I was downplaying your knowledge. Didn't mean it to sound that way at all.

Your issue sounded very familiar with the drop in volume, yet the other channels worked. Happened to me once, which is why I jumped in.

Anyway, good luck with getting it back up and running. When you do find out what it was, please post it and let us know. I'm real curious as to what it is now too.
 
TysC":3fl1u1mv said:
Hi Bill,

Thanks for the reply, but I have successfully modded quite a lot of amps/pedals myself so i'm well past the "try a preamp tube" idea. I just haven't opened it up yet to inspect.

The manual actually does give a tube breakdown, channels 3 & 4 use the same gain stages.

I'm not sure what type of recto's your using, but the Roadster is what i have in question.

Cheers,
Click to expand...

Hey TysC,
Just wondering if you found out what the cause of the volume drop was in your amp?
 
Hey Tyson,
I forgot I had this memo from Mesa about volume drops/cutouts. I'm not saying this is what it is, but Mesa put out a memo about it.


"Mesa Memo

SOUND “DROP-OUTS” / INTERMITTENT SIGNAL

One Possible Cause



Most (but not all) Mesa/Boogie amplifiers have one or two “cathode follower” tube
stages in their preamps. Tube selection is CRITICAL in these stages.



Specifically, in a 12AX7 tube used as a “cathode follower”, the voltage difference
between that present at the cathode, as compared with the heater voltage, can be
withstood or tolerated by certain types of tubes, whereas other tubes will fail. The
failure of a “cathode follower“ tube will cause sound dropouts or signal loss.



For the past few years, Mesa has been using two types of 12AX7 tubes: ones
originating in Russia (Sovtek EH), and ones originating in China. The Russian (Sovtek)
tube is NOT reliable as a cathode follower. Of the tubes we are using today (March
2008), ONLY THE CHINESE 12AX7 IS RELIABLE AS A CATHODE FOLLOWER.



In conclusion, if you are troubleshooting for signal dropout in a Mesa/Boogie amp,
suspect a cathode follower tube, and try replacing it with a Mesa 12AX7 that is marked
as “CHINESE” (silk-screened on the tube itself).



Below is a partial list of Mesa amps and cathode follower tube locations:

GUITAR AMPS BASS AMPS

Lone Star & LS Special: V3
M-Pulse: V2
Stiletto: V3 & V4
Venture: V2
Road King I: V3 & V4
Big Block 750: V4
Road King II: V3 & V5
Titan: V4
Roadster: V3 & V5
M2000: V2
Dual & Triple (2ch or 3ch:) V3 & V4
Bass 400+: V2
Tremoverb: V3 & V4

ANOTHER POSSIBLE SCENARIO may occur in the “SPONGY” (or on some models,
“TWEED”) power setting: the reduced filament voltage may cause very low output from
a RUSSIAN preamp tube. Again, the recommended fix is to replace the “sagging” tube
with the CHINESE type of Mesa 12AX7 - which are more immune to this type of failure."
 
You must log in or register to reply here.
Back
Top