Tweaker 15 Combo troubles... advice?

[Vetseun]

I’ve been an extremely happy Tweaker owner for almost a year now, but my Combo has recently started giving me a bit of trouble.

A while ago I started experiencing some intermittent problems with my amp. After I’ve been playing for a while I’d experience a pretty severe drop in volume. The amp’s tone would also be very muffled. Also, when switching the amp to standby I’d get a hiss/crackle sound coming from the speaker. I initially thought that it might be the power tubes, so I swapped in a brand new pair of TAD 6v6GT-STRs, but the problem persists. The new tubes aren’t redplating that I can see.

The problem also seems to appear whenever I switch between the vintage/modern voicing. I discovered this when the amp sounded very muffled and I tried flipping a few of the mini toggles to see if I’d maybe accidentally flipped a switch. If the amp is acting up (ie muffled tone and decreased volume) I’d switch the amp to standby and flip the vintage/modern switch back and forth a couple of times and the problem would then go away.

I have no idea where to start looking and I’m based in South Africa, so I can’t take it in to Egnater. There are a few amp techs around, but I can’t really point him in a direction…

Could it be that the vintage/modern mini toggle is faulty and that it’s vibrating out of position or something? Would this be something I could test?

The tubes aren’t red plating, so I don’t think it’s a voltage issue, but could the cathode bias be set to hot? We’re on 220v in South Africa…

Any advice on how to troubleshoot the problem a bit more would be greatly appreciated.

 

[shimmilou]

Hi Vetseun,

Have you tried the preamp/PI tubes? Using one good 12AX7, try it in each position, one at a time to check.

 

[Vetseun]

Thanks for the reply... I replaced those with brand new tung-sols a while ago, so it hadn't occurred to me to try and swap them. I'll definately give it a go... with the problem being intermittent is there some other why to test whether the 12ax7's have gone bad?

 

[shimmilou]

Maybe a good tube tester. But really, for most people, the best tube tester is the amp itself. It's simply that the tubes are the source of most problems, not always, but most often. And substituting known good tubes is usually the easiest, quickest and cheapest thing to try, especially if you don't have much test equipment, or don't have money for a tech. Troubleshooting is usually a process of elimination/proving, and the odds favor a tube problem. You only need one 12AX7 to try each position one at a time. If not a tube issue, then the amp would need a good inspection by a knowledgeable tech, in which case I would check for warranty.