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Tubes - when to replace?

4/19/1998 9:25 PM
dave bush
Tubes - when to replace?
i just bought a used amp Acoustic brand (anyone heard of these?), it has four EL 34s in it. It sound okay, though maybe the tubes need replacing. I have tried swapping some of the 12 ax7 preamp tubes around, and the reverb improved with certain combinations, which may indicate that some are more worn than others or that everything could do with replacing. Do preamp tubes wear out much? Its a little hard to tell at the moment, as the amp is quite complex, it seems to have 5 pre amp tubes for a single channel amp (it is very flexible). I spose one is the phase spitter. Anyway, I guess the big question is when do I replace the power tubes? Are there any visible signs? The amp sounds okay to me except some of the tone controls arent that responsive (though then again it also has a graphic eq, so very unsubtle tome modifications can be made).  
Any advice is welcome!

Steve M. Dave,I've had two different... -- 4/20/1998 7:58 AM