Mesa Mark IV no filament on V1, front panel lights not lighting. Help please.!

[Redline]

I was playing my Mk 4 to other night and I suddenly lost sound. I looked in the back of the amp and noticed that v1 was not glowing. I replaced the tube with a new tube. Of course it's never that easy. I pulled the chassis and checked everything relative to that tube and everything is in spec. What am I missing?

[Mick Bailey]

V1 is powered off 12.6V dc. Check you have 15v going into the regulator VR12 and 12.6V coming out of it. Does the footswitch work? If not you've lost the 15v supply.

EDIT; This applies to Mk IV A - the B is different. Check which amp yours is.

[Redline]

Mine is a B. The foot switch hasn't worked since I bought it. I use a Kool Kat aftermarket switch.

[Redline]

R383 was blown. I replaced it but that didn't fix the problem.

[Redline]

On VR12 I have 4.3v and 5.8v. I get front panel lights with the tubes out but no lights with the tubes in.

[Mick Bailey]

AFAIK VR12 applies to the A version. Can't see R383 on the schematic - where is that located?

Measure the voltage on the socket pins 4 & 5 of V1. Should be roughly 12v .

Can you post the schematic for your particular amp, or a link?

[g1]

schematic:

[g1]

I get front panel lights with the tubes out but no lights with the tubes in.

How about with only V1 removed, do the front panel lights come on?

[Mick Bailey]

If It's version B, then there isn't much to it. Point F needs to read 12v, if not check voltage at point E and the drop across R124. V1 is powered of its own transformer winding - the rest of the tubes are off another.

[Redline]

How about with only V1 removed, do the front panel lights come on?

Yes. Front panel lights up with v1 pulled.