The Dominator Mk 2 had suffered from melted transformer potting wax running down the chassis covering the valves and entering the sockets. They were literally glued in! Before doing anything else the mess had to be cleaned up! Quite a task I can tell you but the owner didn't want the sockets replaced as he'd just won it on a well known auction site.
This great little Wem Dominator Mk 2 was not quite as nice inside as out. Now it is and is one of the best sounding Wem amps I've worked on. I want one! The tremolo is lovely and the noise from the tremolo channel is now negligible after a fair bit of troubleshooting and a simple mod. The owner is really chuffed with it. I didn't need to change a single component and there's a full set of lovely Mullards in it too, including an EZ81 rectifier. It even has it's original cover!
Full story to follow soon! Happy New Year! Finally found the Rotel noise gremlins hiding in the selector switch. After a thorough service and virtually rebuilding the phono amp, freezing the crap out of the transistors and a lot of hair loss, the amp is back with it's very happy owner! I must say, I almost gave up on this one, but I hate admitting defeat!
Getting the selector switch out to refurbish was real pain. One of the copper saddles pinged off somewhere and took me ages to find! Think I need another bench for these diffcult patients. All said though, it's a terrific amp from a lost era, so worth saving. +2 This Fender Concert hadn't been used for a few years as it kept blowing HT fuses. I found a dead short from the screen supply to ground! However, it still blew the fuses when left overnight, due to the huge inrush current into the fully discharge caps at switch on. A full recap sorted the problem but it needed testing over several days just to be sure. Another great sounding handwired Fender. Shame there's no tremolo!
Read more here! Here's a bit of a rarity. Normally I don't like solid state stuff because it gives me a headache! This time only a minor one. Why wasn't it working? Symptoms described were, power amp works if you plug into effects return but the preamp is just a white noise generator. Someone was in there, gave up and didn't even bother tightening the pot nuts. I did that and to my surprise got a signal through on the scope. The pots were all scratchy but reacted well to a spray clean. So I thought it was fixed. However, through a speaker all I got was white noise, hum and the faintest signal at full volume.
Why did the signal generator output work when the guitar didn't? I couldn't find any loose grounds but signal tracing from the input I found the first OP amp wasn't passing the signal on. Luckily I have a small stash of LM1458 chips. There's a knack to getting the 8 pin units out and I always put a DIL socket in there just in case they blow again. I guess someone foolishly overloaded the input at some point. Anyway, it all sounds good now and full output can be measured through a dummy load before clipping. The power transistors run very cool on that massive heat-sink! Here's a nice clean example of a 1986 JCM 800 Lead Series, in for a pre-sale service. It hadn't been used for years and now it had poor tone and a fairly loud hum. All the components checked out good but the output looked very poor on the scope. A new set of JJ EL34 and all is well again! love the clean channel with a splash of reverb. The high gain diode clipping channel sounds best with all the treble rolled off to my ears, and is actually pretty good.
I think you'll agree, inside is mint! The only damage was to some of the pots had bent shafts and a couple had broken splines with insulating tape to keep the knobs on. They all worked fine after a spray cleen and their nuts tightened down (painful!). Another legendary monster of an amp leaves Oldamps lab sounding great and with a clean bill of health.
Story and a few pics for anyone who's are interested. Just click on the pic! They certainly built these very well indeed in the 70s, and it's still totally original!. Well maybe not the screws on the back! Had to make a special tool to get them out before I could service the thing! Not a bad component in there except the mish-mash of odd valves. An old Mullard, an ITT, a Seimans and a Teonix. Here's their current draw in mA at 470V:- 32, 24.5, 35.6 rising to 40.2 after a few minutes and 18. On my valve tester, the Mullard tested very strong but is microphonic. Nuff said. A new matched and burned in set ordered. Now to fix the light in the power switch!
Nice trio of long plate ECC83 too!. Not sure of the brand though MValve? |
Andy here
Always looking for work fixing your amps. I prefer older non-pcb stuff, but I've had quite a few modern valve and solid state amps lately. |