Blowing my Fuses!

Yikes! I didn't realize it could actually be dangerous.

Tube Nube wrote:Yikes! I didn't realize it could actually be dangerous.

It's rather akin to leaving your cook-stove on unattended for weeks at a time. Nothing good can come of it. You won't hear a tube red-plate unless you've got music going through it.
Just counting on my fingers, if the amps were on for 12 hours/day for 4 years, that's over 17,000 hours. Given that the life expectancy (correct me if I'm wrong, Dr. McShane) for new-issue Russian tubes is probably 4,000 hours, I'd say you got your money's worth out of those KT-88s.

Well, it looked like the problem was solved with the discovery of a bad power tube, but apparently it's back to its fuse-blowing tricks again.

The tech guy looking at the amp has my schematic, but asks if there is a "full" schematic available, or, in particular, a schematic of the pentode/triode switching portion of the circuit.

A google search gets me lots of copies of the power supply / left channel schematic, but I can't see the pentode/triode switch (could be my schematyxlexia).

So thought I'd pass the request along.

Next on the list, I think, testing the caps and the trannys. But first, a trip to the fuse store. My friend can't purchase proper fuses in his small town just South of Calgary, so I'm off on a little road trip.

What was it George Harrison said? A long and winding road?

Ok, Im sure all are sick of me flogging this thread to death, but I wanted to post up a substantial update. Roy gave me the names of a few good techs who could and would be able to fix my amp. I knew them all by name, and chose the only Canadian, Don Sachs in Nelson BC, only to avoid cross border hassles.

So while being repaired, I took advantage of the opportunity to have the new octal driver board installed. Im addition, Don thought I might be interested to consider a few othe component swaps, like silver oil caps, etc. And, of course, he was right.

So I just wanted to post a shout out to Don for his great service. He did the work fast and fair. Communication was excellent! We also had a good couple of chats sbout thoughts about future upgrade diections--something that's also been on my mind for a few months.

This has been so helpful that I can almost say Im glad my amp broke. It forced the opportunity to learn a few things Im glad to know.

And now I have my amp back home in its proper place and sounding great!

What did the problem turn out to be?

Hi Bill,

Don was pretty sure it was a bad connection on the driver board, and suspected something like one of the pot resistors, but he didn't isolate it. That's because I decided to take advantage of the opportunity to upgrade the amp while fixing it. So this included installing the new octal board, as well as some other components, like silver oil Mundorfs in place of the PIO's and a few other things like that.

We agreed it was most efficient to do the upgrades, run the amp, and if the problem isn't fixed, then pin it down for the fix. Fortunately, from a monetary perspective, but unfortunately for our enquiring minds, the cause remains uncertain.

It was interesting, though, to hear from Don that he would have been extremely surprised had it been a transformer issue, and he seemed almost as confident that it wasn't likely to be a cap.

Now that I have the amp back, I'm sure enjoying it once again, and I'm eager to get the new speakers finished so I can REALLY hear the thing.

Noob, wonderful to hear.
My problem (similar to yours) was a poor or non-existent solder connection on one of the three legs of a bias pot on the PCB. Those are almost impossible to spot without an electron microscope.
At any rate, glad yer up and running!

I read some good soldering advice in the instructions for my Transcendent pre-amp, which I only built after my power amp -- that was to solder each connections from both sides of the circuit board!

Perhaps had I gone back . . . then again, if it was a pot, I likely wouldn't have left enough room to get at it from both sides.

Anyway, the amp has been professionally overhauled, updated and tested by one of our gurus who has a real passion for this stuff. I think he can bank on getting more jobs from me!