What happened?

[Spirit of 76]

I've had my 2466 for about 3 months now and it has been working great with the master volume going no higher than 3 and my detail and body at 9. So at practice tonight I decided to try and dime the master volume with the body and detail still at 9 and see what kind of play my volume knob on my guitar would have. I also wanted to get some power tube distortion going. As soon as I did this the amp cut out. No sound! I turned it back down and after a minute the sound returned. I started thinking maybe a bad cord? Got a new cord. Started to play again and this time I took it up to 7. Same thing happened. I kept it at around 3 for a while and everything was cool so I slowly started to crank it up. Everything was fine up till 5 and as soon as I pushed it to 7 the amp cuts out for good!!! No more sound the rest of the night. It did seem to have more heat coming from the tubes after this happened. So what happened?

[Slashwannabe1]

Faulty volume pot probably. Possibly dirty/dusty.

[Spirit of 76]

Thanks for the reply Slash. I don't think it is the pot because usually you would hear some crackling and pop noises for a while before it went bad. I heard no such noises and the knob is pretty smooth ( not loose when its turned ).

[DogFalcon]

Yeah! I agreed with that too! Maybe a dirty volume knob.

[Slashwannabe1]

Thanks for the reply Slash. I don't think it is the pot because usually you would hear some crackling and pop noises for a while before it went bad. I heard no such noises and the knob is pretty smooth ( not loose when its turned ).

Probably wouldn't hurt either way to spray some electronics lube into all the pots to keep them fresh.

Its also possible that a pair of your power tubes have gone out, allowing you to have low volume but not high. Do you notice any greyish/white looking ash type substance inside any of your power tubes? Any new hum?

Also are you using the correct unshielded speaker cable?

In any case I'm sure Steve D will come on with the best solution soon :)

[SteveD]

Could be a number of things but I'd suspect the output valves first. Is the HT fuse blown?

[DeanM]

SteveD, cant be the HT fuse cos he said sound came back when he lowered MV again.

I am 90% sure something similar happened on here before. and i think it was that when the MV was raised and the power tubes start gettin pushed harder they kept cuttin out. so id say check the valves aswel. i think it can happend that the tubes can work fine when not pushed to far but fail when pushed hard.

does the sound stop instantly? or does it play for a sec and then "drop out"?

[Spirit of 76]

Thank you for the replies. The fuse was not blown. The amp turns on and the tubes all glow but there is no sound. The sound came out a little bit say half a minute or so then cut out. The sound came back after a minute or two the first two times it cut out and then no sound ever came back after the third try.

[auss81]

Why don't you try changing tubes? I suspect could be a faulty tube.....

Try swapping V1 and/or V2 and so on..... If You are able to bias, try also swapping the KT66s.....
As SteveD said look at the tubes...

Once I had a similar issue and I found was a faulty 12AX7 in V1.

I know tubes may be expensive, but I would give it a try.

[SteveD]

SteveD, cant be the HT fuse cos he said sound came back when he lowered MV again.

If you read his post he said the amp didn't come back on at all after the third time.

-- Sat Apr 17, 2010 11:13 pm --

Thank you for the replies. The fuse was not blown. The amp turns on and the tubes all glow but there is no sound. The sound came out a little bit say half a minute or so then cut out. The sound came back after a minute or two the first two times it cut out and then no sound ever came back after the third try.

I would suggest swapping out the preamp valves one by one first.

[DeanM]

SteveD, cant be the HT fuse cos he said sound came back when he lowered MV again.

If you read his post he said the amp didn't come back on at all after the third time.

I did read the post. i read this part...

As soon as I did this the amp cut out. No sound! I turned it back down and after a minute the sound returned.

thats why i didnt think it could be the HT fuse.

[SteveD]

Everything was fine up till 5 and as soon as I pushed it to 7 the amp cuts out for good!!! No more sound the rest of the night.

This is why I asked about the HT fuse.

[Spirit of 76]

Thank you everyone for all the input. I will try and find the bad tube. I hope it is just a tube. Steve why do you think it is a preamp tube and not a power amp tube? Would'nt the amp have cut out at any volume when I cranked the body and detail? Do the preamp tubes get pushed harder when you crank up the power stage? I really do not know to much about amp electronics.

[SteveD]

I actually pointed at the power valves in my first post if you notice and it may still be them. However, when you said the HT fuse was not blown I thought it was worth checking the preamp valves as well, just to make sure nothing silly is going on. There are many faults that could cause your symptom and unless I can open the amp up personally to have a look it is very difficult to diagnose.

[Spirit of 76]

I have not had a chance to take the amp to a tech yet but I turned it on at practice this week and it worked fine. I did not dare take the volume over 4. Its working good for recording purposes but will have to get it looked at before going live again.