3Ch Dual Recto - no volume

[warped]

I'm hoping this is only a tube issue (I will have a play around tonight).

Last rehearsal I noticed after taking the amp off standby it took a while for sound to start coming through - didn't think anything of it at the time.

Then last night, I had the amp up pretty loud (rehearsal volume) and when I switch the effects loop on the volume dropped significantly (I have a Visual Sound H20 in the effects loop. I took the pedal out and ran a patch lead from send to return and got the same thing). So just played the first set without using the effects loop.

I put the amp on standby, have a break, come back and now my amp has almost no volume at all, on all channels, even when I switch the effects loop to bypass. I switched the V5 pre-amp tube (mainly coz it's the only one I can get to without taking out the power tube or removing the amp from the chassis and it had no effect. I switched leads (guitar lead and speaker lead) and switched guitars.

The amount of volume I get is about as loud as the amp normally is on 0 (can just hear the guitar coming through the speaker cab).

I suspect it may be the V4 pre-amp tube looking at the manual, but it's interesting that with effects loop on bypass I still have the same problem (Is V4 still in the circuit with effects loop on bypass mode).

And the fact it's on all channels makes me think it might be V1. I'll do some swapping tonight - just thought I'd check if anyone else has had these symptoms before?

Cheers

 

[elvis]

Try the phase inverter.

 

[warped]

Thanks elvis - I tried swapping the V5 (phase splitter/output) pre-amp tube in the rehearsal room with a new one and it made no difference to the sound/volume at all..

I'll try cycling through all the pre-amp tubes one by one tonight and see if I have any luck.

 

[mmount]

check the power tube board for any burned spots...its a pretty common problem with 3 channels rectos. Also is one tube burning super blue/orange?

 

[warped]

All power tubes are burning fairly blue and pretty much look exactly the same - and have done so since I got my last re-tube about a year ago - I'll take a pic tonight.

They are a lot blue-er than the other guitarist's Stiletto (he's running stock Mesa tubes, I had WingedC 6L6's put in and the amp biased to suit - I believe they were biased using resisters or something as they aren't adjustable bias, amp tech is very well regarded, not just a backyarder).

I didn't smell any electronic burning smell (I have smelt this when something died on my other amp a few years ago)..

 

[Neptical]

My old Rec did the same thing.

End result: Power tube failure.


[but just in case I would check V1 just to be sure.]

 

[warped]

Thanks Neptical - I'll check the pre-amp tubes tonight - if still no solution I'll take it to a tech for new power tubes and a service...

I have the old set of power tubes - that aren't matched to the current bias - I could also try swapping one out a time on the power section - might not sound as good, but I guess it might at least reveal if it's a power tube issue..

 

[warped]

I have a single brand new mesa 12ax7 - I swapped this tube with every pre-amp tube one at a time and it made no difference. I replaced the power amp tubes with my old set (which were still good/working, I re-tubed it prior to recording as the amp had been used a lot) and it still made no difference - so unfortunately it's not just a bad pre/power amp tube problem

I know very little about electronics, but I had a look at the boards (didn't touch anything) and the only think that looked odd/possibly a problem was the contacts/solder spots around the 3 wires circles in red below looks to be burnt. I think the part circled in yellow may be where the amp tech adjusted the bias?

I'm going to take it to an amp tech, but any ideas?

 

[mmount]

that stuff looks good

you can change the tubes out yourself... to see if she works.

you looking for black spots on the board... pm your phone and Ill send u a pic of my 3 channel rec that had some burn spots on board. U can just match up my pic up to your board

 

[warped]

Hi mmount,

I've swapped out all 4 power tubes with another set (my old working set/backup set) and it made no difference.

I swapped out every pre-amp tube one by one and it made no difference.
ie, I have one brand new Mesa 12ax7
I swapped it with V1 pre amp tube, turned the amp on and played, still no volume so I put the original back in V1.
then I swapped the brand new mesa 12ax7 with V2, turned on the amp, sill no volume so I put the original back in.
continued through all 5 pre amp tubes.

When I say there is no volume I mean the amp is very very quiet - like the guitar is just audible, even when I have the volume running very high. The tone at the this very low volume is ok, not staticy or fuzzy. When the amp was working fine I would have a very low volume when I had both channel and master volumes on 0. This is what it sounds like. If I turn the volume up very loud ( channel 3:00, master 3:00 it gets a touch louder).

 

[mmount]

man that sux ! but thats what mine did when i had the burn spots on the board i was telling u about.

 

[warped]

Thanks mmount - I sent you a PM.

Here is the rest of the power section board (I hope it's not too big to post here)..

Does it look ok where you had the burnt/black spots (If I included the right area of the board in the pic)...

 

[Neptical]

Hmm-don't see anything that looks weird (caps/resistors) at least in the pictures above...

If you've gone through all the tubes in both preamp and power sections and everything appears to be good..

hmm..what's next?

Closely inspect for loose wires while you have it open.

Hopefully it's not a transformer issue.

 

[warped]

I'll take it to a tech - I don't want to go poking around inside it if the caps can hold a big charge.
I'll let you know the verdict ... Sounds like it's going to co$t me....

 

[JW123]

Dont mean to be a smartass, but have you checked all your guitar cords? Checked your guitar? What about your speaker cord?

Thru the years Ive done some silly things like that, so Im just asking.

Good Luck, hope you get it figured out and if its in the amp please share what happened!

 

[warped]

Hi MW123 - yeah - I swapped speaker lead, guitar, guitar lead... I'm running guitar straight into amp input, nothing in effects loop, patch lead in effects loop, different patch lead in effects loop, effects loop set to bypass mode..

 

[mmount]

yea take it to a tech...mine had a problem in the bias circuit but I cant tell from the pics on yours.. look behind those ribbon looking wires atleast thats where my problems was.

 

[warped]

Dropping it off to the tech today - I'll let you know when I find out (maybe a week or so).
Thanks for all the help guys!

 

[R_ADKINS80]

those 3 resistors soldered together in parallel like that look fishy to me. If the tech said he did it to "bias" up the tubes last time then that's a major fail.....the biasing resistors are on the smaller board that house all the jacks, pots and switches to the back of the amp.

 

[warped]

Thanks R_ADKINS80 - I'll see what comes of it.

The amp has had a 120V to 240V power transformer conversion (would the piggy back resistors have anything to do with that?)

And has had the Power tubes replaced and 'biased' - I only assumed those extra resistors may have had something to do with biasing from looking at the 'installing a bias pot' instruction page on here which specifically mentioned something about the resistor which has 'piggy back' resistors soldered to it on my amp. I don't know how/who put those there or for what purpose - just speculation on my part. I might ask him about them when he gives me the diagnosis?