Tubes in Gibson Skylark

["Priest, Jim" <Jim.Priest@xxxxxx>]

I'm looking for some advice from the amp wizards again. I just acquired a Gibson Skylark GA5T amp, early 60s vintage I'd say - two inputs, controls for volume and tremolo speed, 10-inch speaker, that's it. Playing my JT-30 through it sounds good, but I reckon it could be better. I checked out the valve configuration and am a bit puzzled: it has 1x6X4 (Dumont), 1xEL90 (Mullard), 1x6AQ5A (RCA) and 2x6EU7 (Sylvania). I took a look "under the hood" and as far as I can tell, with my limited electronics skills, the 6EU7s are the pre-amps and the power tubes are the EL90 and the 6AQ5A. Now shouldn't power tubes be "balanced" ? Are the EL90 and 6AQ5A equivalent tubes ? Does their being different affect the sound the amp puts out ?

What suggestions would anyone have for replacing any (all?) of this tube setup ?

Jim