Mark 4 Pre Amp Valves

[Yunker100]

Hi All
Wondered if anyone could advise. Decided to try a new set of Hi Gain Pre Amp valves and, after fitting, the output seemed less than it was with the original set. After an hour or so of playing the output as getting less all the time. I've since put the old ones back in and all is well. I'm going to return the set from whence it came but wondered what could have been the problem. I definitely put them in the correct positions.
Cheers
Yunker

 

[sduck]

Bad tubes. There's tons of them out there. What kind were they, and where did you get them?