Power Tubes... Can they cause volume (power) loss as they age?

[deeaa*]

60W tube watts should really be plenty. Indeed the tubes may be dying, and with such old tubes I'd definitely change them already rather than risk a catastrophic tube blowout, but it might simply be that the 4x12" yields so much more dB at lower frequencies than your single - not to mention open-back - does that it seems like it's not enough. Closed-back and multiple speakers pump air so much more efficiently. It doesn't need that much extra to sound way overbearing in comparison with a tinny open-back single speaker.

Speaker efficiency after all is way more important for volume than actual wattage. Some 36W like my old Ceria was is quite enough to play along with 100W Marshall rigs when used with a suitable 4x12" with V30's etc. in it that are pretty efficient, but it could hardly be used with a drummer using another 2x12" cab I had.

Also, EQ and gain etc. settings can have a huge impact on volume. Despite I use a 100W tube Marshall head now, my 4x12" isn't the most effective plus my EQ/Gain settings are pretty low, I find that I have to turn the amp past halfway mark to be well heard! I really need to push the lead master volumes to near dimed to really be able to scream over the rest of the band.

So it might also be that you're far from 'unity gain' within the amp structure, i.e. at some point some stage is not feeding full signal to the next stage due to low gain setting or whatever, but I'd first venture it's the cab/speaker inefficiency that is to blame here.

And for devil's sake change those t00bs already :-)

[tunghaichuan***]

It sounds like your power tubes are dying. Loss of volume is a sign that they are on their way out.

Are the Sovteks really 6L6s or are they the 5881s? The Sovtek 5881 isn't a real 6L6 and will put out less power in a circuit designed for a real 6L6, like your Peavey. The Sovtek 5881 needs a different primary impedance on the the primary of the OT and higher plate voltages to produce the same power as a real 6L6.

If they are real spec 6L6s, they are probably on their last legs. Modern production tubes don't last nearly as long as NOS types.

I'd definitely retube with a *real* set of 6L6s, 60W of tube power should bury any 80W ss amp without breaking a sweat. If fact, if you can swing it, you may want to get a set of NOS 6L6s, RCA, Sylvania, and GE are all great. If you can find them, the Sylvania STR-387 and RCA 7581A are excellent choices, but are hard to find and are expensive.

Also change the PI tube. If it is getting weak, it may not be driving your power tubes to full output.

Since the amp is almost 20 years old, I'd check the filter caps in the PS for good measure to make sure the PS can supply necessary current.

In fact, you may want to get the schematic from Peavey and go through it with a scope to see if there isn't some other weirdness going on.

[guitartango]

Solid state amp ----- please do not swear on this forum