6L6 PP problem

[slideman82]

I have some noise issues with a 4 6L6 power amp, similar to blocking distortion, but this noise appears at half power (about 50 or 60W), even without signal. Tubes aren't matched, and 3 of them are quite old, one is new. Could be a tube mismatching problem?

 

[tubesteve]

can you describe the noise a bit more precisely? with or without signal?

 

[richwalters]

More info S.V.P. Since history is unknown, changing all the tubes may be a good idea.