Problem with my Silver Jubilee 2554

[Hudson]

Hi everyone,
This is my first post on this forum; but I'm a reader since ages.

I've got an issue with my beloved 2554 combo.

I 've got this amp since a year. I've changed all the tubes and biased the power tubes when I bought it.
The amp was working fine, never had any problem until now.
Here is my problem : I got a great loss of volume on the clean channel and no sound at all on the lead channel.
As I said, tubes are near new (JJ & EHX) I don't have any buzz or hum.
Any ideas?

 

[MarshallDog]

I would start by replacing all of the preamp tubes (or at least rotate a new one through until you locate the bad one(s)), I think it is the best place to start AND a loss of volume on the clean and nothing on the lead would make me think one of the triodes or more in one or more of the tubes has checked out. I know you mention they are new but I've have new CP tubes and NOS tubes fail right out of the box or shortly there after. If it was anything too major, my guess would be you would have a loss/no sound on all channels. I'm sure some of the other MF'rs will have some good ideas also.

Also please introduce yourself under the new member Community ---> Introduce Yourself section

 

[mickeydg5]

That could be a faulty V1.
It may be the channel switching relay.
It may be the LEAD MASTER potentiometer or things connecting in that area may need to be checked.

 

[Guitar-Sam]

Try a jumper wire between send and return on the fx loop.Thats a known problem with the Jub loop getting dirty and causing issues. Can't hurt to try

 

[Hudson]

Hey thanks for the help.

Looks like it was V2 who was faulty.
I hope that this problem is gone for good.

 

[mickeydg5]

That does not make sense. Both channels go through V2 equally.

But oh well.


Did you have the LEAD MASTER volume down low?

 

[Hudson]

That does not make sense. Both channels go through V2 equally.

But oh well.


Did you have the LEAD MASTER volume down low?

I know I was suprised by the result as well.
Maybe v2 had a very low output level that didn't reach a specific threshold for the diodes bridge (of the lead channel).
The lead master pot is now working as usual; when I had the proble it was not working at all.
I'll keep an eye on it anyway.

 

[MarshallDog]

For what its worth, I tried a 5751 in V2 and tye volume on the lead/dirty channel was much lower than the clean...I can never remember the exact names of the two channels. Anyway if V2 was bad in some way I could see this happening. Glad you got it fixed.

 

[mickeydg5]

I think I see what is happening. The two channels have different interactions with V2A. A weak V2A may mean higher internal tube resistance. The LEAD channel has a route to ground and if the tube resistance is up then the signal is forced more to ground. The RYTHYM channel may loose some higher frequency but will generally keep its signal level.

 

[Hudson]

Unfortunately the problem is back.
Exactly the same issue. I did not have any problem for ten days and tonight, while I was playing, volume goes down and no more lead channel. I can't believe my new V2 is blown away. This must be something else.

The last time when I was testing my premap tubes I also switch the power tubes but I can't figure out that it have anything to do with my problem.

 

[mickeydg5]

Try another tube in V2 to be sure.

Use electronic contact cleaner on the tube pins and tube socket prongs where pins contact prongs.
See if that helps.

I mentioned resistance of the tube affecting the signal but a bad contact at the pins, bad solder connection, bad wire or bad board trace can do similar.

If the cleaner does not help then all of the above mentioned should be checked and verified.

 

[Hudson]

Ok, It's fixed.

I took Mickey's advices and use contact cleaner on the tubes sockets and on the pots.
Now my amp is working fine again. Looks like it's now a little more trebbly than it use to be.

Thanks for the help.

 

[mickeydg5]