Marshall DSL50 feedback

Sorry if this is the wrong place for this thread.

I have a DSL50 amp that I've been using for about 1 year now without issues. A few nights ago I started getting some insane feedback from the amp. It was near the end of the night so I shrugged it off. Unfortunately a few nights later when I plugged in the feedback returned immediately. I used to have to fight to get feedback, but now it comes in as soon as I run some distortion, either the onboard version or through my effects pedal. I've run several guitars straight into the amp and I get the same result, unbearable screeching. Could it be the electonics inside the amp? Tubes?

Any help is much appreciated. This was an expensive head so I would hate to have to sell it and get something cheaper.

TIA.

adrian.

[Mark Kane]

Try swapping the preamp tube farthest away from the power tubes with the preamp tube closest to the power tubes and see if that makes any difference.

Sorry but I'm not much of an amp expert. In the back of the amp there are 6 tubes from left to right:

1-small tube with an outer (protective?) cover with spring
2,3,4- small tubes with no covers
5,6- large tubes with no covers.

Which ones would you recommend switching?

TIA.

adrian.

[John Phillips]

Swap 1 and 4 first (what Mark says). If that doesn't cure it, swap 1 and 3 or 1 and 2.

You've probably got a microphonic preamp tube, and the most sensitive to this in the amp is #1 (under the metal cover, which is partly why it has this) because it is at the start of the amplification chain.

If that's it, it may be worth upgrading all the preamp tubes. The stock ones fitted in most modern amps (including Marshalls) are just 'average' tubes, nothing special.

Is it still under warranty? Marshall are giving 3 years now (apart from on tubes) so if you bought it new, it will be covered if it's not a tube problem.

Thanks for the suggestions! I will give them a shot.

As far as new tubes, what tube would be a good choice to upgrade to? The stock preamp valves are 4xECC83's. Should I also look at upgrading the power amps?

Thanks,

as

[jlagrassa]

It sounds like you have a microphonic pre amp tube, you could try the old pencil test with the amp on tap each preamp tube and see if one flakes out on you.
I use all JJ ECC83S preamp tubes in my DSL 50 I also use JJ E34L for power tubes the JJ's really help keep the high end under control

i did notice that of all the preamp tubes, the first (microphonic?) tube was not hot at all while all the other were very hot after playing for several hours. maybe this is the culprit. i will replace it and see if that helps. thanks all!

as