Independence Day amp refurb
About 15 years ago my dad came home from some a garage sale with this Custom Kraft 600A. He got it for $5. Inside the guts the manufacture date says July 4, 1969.
At the time I found it a little weak, but a neat conversation piece. Over the years I've played Fender, Marshall, Mesa Boogie and Orange amps. This is the one I never let go of, even though its sound has deteriorated in recent years. So a while back I pulled it out and began rediscovering its sound. It's made by Valveco, the same company that produced the renowned Supro line, for which Jimmy Page helped make famous by recording most all of Led Zeppelin's first album on a small Supro combo not much different than the electronics found in this little guy.
While the tone has always been sweet on this amp, now it fizzled. The distortion was weak and sound pressure weaker than you would expect from a 30 watt tube amp. I started with all new tubes, but that didn't do it. I suspected a three-stage electrolytic capacitor in the power amp circuit. Given that it was almost impossible to find a replacement for a 40-year-old specialized part like this, I simply used three seperate capacitors. One was a little hard to find in the variance I needed, but dad and I replaced these as well as the two big ones you see (now blue).Well, the amp got its sound pressure level back, but still had issues. The "fizzle" at the end of a tone was more evident at high volumes. So I ordered a few more replacement capacitors for the input circuit in hopes that one of them would be the culprit.
Earlier this week I snipped the 40-year-old capacitors out and replaced with modern ceramic type capacitors. The are much smaller and the difference is apparent. I could probably sell this unit for a few hundred bucks, but I've got about $60 in it now (mostly from the tubes and the one hard-to-find capacitor) and well, about half of its guts are my work now. So I may just transfer the unit to a smaller box and make it a small head. I've bypassed the speaker in favor of a 1/4 female phono where I plugged in a 4x12 cabinet. It sounds great and is really loud for such a tiny box.
If you have an old amp that has lost its luster, I suggest holding off on replacing expensive vintage tubes. Electrolytic capacitors can go bad after about a decade under certain conditions. And you can't tell by looking at them. Crappy film capacitors might look horrible, but test fine. Pristine canister parts may be shot from a surge or excessive head that you can't see. Mouser.com has a pretty good selection and unless you have an oddball part like one of mine, you're looking at only a dollar or two per capacitor. Use gator clips to defer heat when soldering and fire up the after each one until you find the culprit.
This amp beats anything its size out there today, and its one of a kind.
