blackstar ht-40 clean channel gets distorted

[jeimatt]

Hi! . After two weak break i played with my amp today in band rehearsals. clean channel got distorted sound at low volume .. never been that kind of problem. . . that spoiled my day.

i changed preamtubes from stock tubes to JJ ecc83s about two months ago. is it possible that those JJ tubes are broken this quick?

i bought my amp ago year ago. . .

thanx.

[egladden123+]

I have the same problem except low power and distorted sound on the clean channel and I have the factory tubes still in it and only use it about once a month. I have had the tubes tested and all still are good.

[thephantum]

If the OD channel is fine and only the clean channel has an issue, it's most likely the preamp tube in V1. Before you reiterate that the tubes were tested:

• a) 12AX7's have two triodes. Very often a tester will only check one.
  b) Testing a tube is not a "be all end all". A tube can test not showing any shorts and have decent Gm...but when put in an amp, still have issues/sound like crap

If the above symptoms are correct, the best test is going to be to swap the preamp tubes. If the problem moves to the OD channel, you've found the culprit...replace that tube. If not, the amp needs to go to a tech...there is something else wrong in the preamp.

If both channels are having an issue then it's more than likely the power tubes.