I used to own an early 80's Concert combo with a single 12. It was versatile and sounded ok, but frustrations with it's tone caused me to trade it and lots of cash in on a 1993 Korg AC30 when new, and I've never looked back. They can be modded to sound MUCH better, but are ok as I suppose. Maybe it sounds better through a Marshall cabinet.
For the tubes, the preamp tubes generally last a long time and may not need replacement, but it can't hurt. For the power tubes, that amp has a bias balance circuit so it is ok to replace them and just set the pot for least hum level. The most important tubes in there besides the power tubes for good tone are the reverb and phase inverter 12AT7's, and the reverb 12AX7 and V1, which is the first preamp tube for both channels. For the first three you want good strong tubes, and for the last one you want good tone first and good gain second.
Preamp tubes in no order of preference:
*Tung-Sol 12AX7 reissue - very nice sound and quality, more expensive than others
*JJ ECC803S - long plate tube with decent sound and quality
*JJ ECC83S - shoter plate tube with lots of gain and good quality and sound
*EI 12AX7 - out of production now but still floating around, often microphonic, but when not, is one of best out there for tone
*Sovtek 12AX7LPS - long plate tube, very good sound and quality, can not use in cathode follower circuits such as in a Marshall or 5F6A Bassman, fine in other spots
*Groove Tubes 12AX7M - a copy of the vintage Mullards...sounds pretty good but spotty quality so far
*Chinese 12AX7 - some like them and others don't, decent quality, good gain and nice tone
*JJ 12AT7 - decent quality and sound
*EH 12AT7 - same as above
*Chinese 12AT7 - same as above
*NOS 12AT7, any type - vastly superior sound and tone to above, not terribly expensive either
Power Tubes in no order of preference:
*Winged C 6L6GC - very good sound and quality, one of best on market
*JJ 6L6GC - same as above, though quality lately has had issues, could be bad batch
*Chinese 6L6GC - haven't tried them myself, though heard they are ok quality and sound
*Sovtek 5881 - one of strongest tubes around, ok but bland sound, extremely reliable
*Groove Tube 6L6GE - recreation of classic GE 6L6, extremely nice sounding but very expensive
*EH 6L6EH - decent quality and sound
*Tung-Sol reissue 6L6GC - very nice sound and quality, one of best on market
I am a dealer for all of these though I try to not advertise that too much here. If you are interested, PM me.
I use Caig De-oxit for pot cleaner, and I can get you this also, though if you have to gig soon, then better find a local electronics store who might sell it. On each pot there is an opening in the back that you can spray the pot cleaner into the pot, and then rotate the shaft back and forth to clean it. Usually the amp is setup so you can get the spray into the back of the pot without having to take the pot out, but not all the time. To clean the tube sockets, you use the same cleaner, and spray on the pins of an old tube, and put it partially in the socket and rock back and forth, and push in and pull out of the socket. You can use compressed air to blow away the residue if you want but it isn't necessary.
SAFETY:
This is the most important consideration when working on tube amps. There are LETHAL voltages inside the amps that can kill you. Capacitors can hold a charge for years after use and they are just waiting to zap you and put a high voltage into your heart. Really to be honest, if you don't know how to be safe with these, you should not be working on them. That said, it is possible to be careful and smart and not get shocked. In most amps, if you turn it off, but leave the standby in "play" mode, then it will drain away most of the high voltage.....but this is not in all amps. It is safest to make a clip lead tool with insulated clip leads on each end, and a 10k 2 watt resistor in the middle, put together in such a way so everything is insulated and there is no way to get shocked from it. Then you take this tool and connect one end to ground, and the other to the first filter cap positive lead in the amp, and wait 30 seconds to a minute. Unplug the AC cord too. Leave this hooked up the whole time you work on the amp and there is no way you can get shocked. Make sure to remove it before you turn the amp on or it will smoke. You can also buy a discharge tool from
www.tedweber.com.
To retension the sockets, you take a very small screwdriver or Xacto knife, and bend the ends of the sockets around in a tighter circle or bend the socket in from the side, depending on which socket type is in the amp. If the voltage is not drained from the amp, you can get shocked doing this. It is best to use something insulated.
Hope that helps,
Greg
