Monday, December 30, 2019

What's On The Workbench?

I originally found this little guy stuffed under a workbench in my Sweet Little Wife's garage when I first moved in. The garage had been a "Man Cave" type place, with carpet and old couches, a little fridge for beer, big TV set, etc., etc, etc. Her first husband would hang out with his buddies after work and sometimes they'd get the guitars out and jam.

This is what he used, a Valco "Supro":

A very simple little "5 Watt" class amp with a single 6V6GT output tube, which is kinda the "little brother" to the ever popular 6L6GC. I showed it to her, and she almost cried, remembering the jam sessions, so I carefully put it away so I could see what it needed to sing again.

Fast forward about 10 years, and I decided to dig it out (she didn't remember me saving it) and give it a good going over. Over the years I collected all the information and schematics I could find for these small Valco amps, so I'm fortunate to have a schematic that matches the chassis 100%.

I flipped it around and pulled the chassis out:

And set it up on the bench:

Yeah, pretty crusty! I got out my EICO tube tester, and checked the three tubes. The rectifier tube appeared OK, but the 6V6 output tube had "shorts", as did the 6SL7GT dual triode input/driver tube.

And it's a "gimme" that the electrolytic capacitors are leaky, as are all the notorious molded paper capacitors, which are all those pink cylinders:

And to add a fourth 1/4" jack input, they removed the fuse holder, stuck in another jack, and scabbed a 4 Amp breaker in there:

Yeah, it's a mess:

Le Sigh.....

So I sent an order off a week or so ago to "Antique Electronic Supply", one of my go-to places for tube parts. Great service, fair prices, and wide variety of parts catering to old tube amps as well as "Luthier" supplies for old guitars, and things like correct replacement Fender knobs. Got three new tubes, some capacitors and odd resistors, fuseholders (I have fuses), and a new leather carrying handle and hardware for this little guy, as the original leather handle had disintegrated long before I first met him.

All I've done so far besides take the chassis out is to brush the dirt off it, and then wipe it down to get the nasty stuff off.  I pulled the "extra" instrument input jack and put a new fuse holder in there. I'm also going to install a proper 3-wire grounded cord on it a bit later. I cleaned the volume and tone controls, 1/4" jacks, and the tube socket pins with some Caig D5 DeoxIT. And I ordered a replacement 8" speaker tonight, as the old one is just too fragile after all these years.

It'll be interesting to see how it sounds after I finish it. Other than the new handle on top, I'm going to tray and leave the cabinet pretty much alone. I'll clean it and trim/reglue any loose covering, but I'm not going to recover it.


  1. Your post called up a flashback of my Dad standing in front of a tube testing machine at what might have been a drugstore.
    I'm guessing the tube was for a TV, but that would be just a guess.
    I think it was before we moved, so it could have been the late fifties to early sixties.

    1. Yes, I, too, have memories of tube testers in every drugstore and some grocery stores back in Joliet when I was growing up.

      We had a cousin who ran one of the best TV/Radio repair shops in Will County, so my Dad never had the joy of pulling the tubes out, testing them, and then the inevitable fight to get them not only back into the correct socket, but also back in the correct orientation in the socket.

      My cousin used to joke he made a lot of money by just putting the tubes back in their correct sockets, and replacing the broken ones.

  2. Replies
    1. Depends on your definition of "play", I guess.

      The only device I currently have that would directly plug in and be usable is one of my microphones.

      I haven't own a musical instrument since around 1975 when I gave away my acoustic guitar and case.

  3. WOW! What a nostalgic beauty. I built an amp but it was all solid state and new parts. I never undertook anything this intense.

    Happy New Year to you guys - Keep warm!

    1. Happy New Year to you two!

      I built about a dozen "Killer Amps" after college. Had a nice little side-line for a while, but got too involved with other things to keep at it.

      The "heads" were solid-state, like a Marshall, but had a separate power supply that weighed about 50 pounds.

      Why such a big, heavy supply? Because these were Thousand Watt amps, and they'd output 1000 Watts RMS into a 4 Ohm load 24/7/365, exactly what the musician friends I had wanted. Today we'd say it's "Transparent To The User", but back then they just called it a "Zarkov Power Block Amp".

      Still have some parts kicking around for it.....

  4. Tubes. How quaint. I have no nostalgia for them.
    Taking a bagful to the drugstore to find out why the TV wouldn't work is not a fond memory. Figuring out that the one that didn't glow might be the problem helped.

    1. And then after finding a bad tube comes the trauma of getting them all back in the correct sockets once you get them back home.....

    2. Wow. I'd forgotten that.
      When I got into TV repair, I never ran into a tube smaller than a CRT. :)

    3. The old "Octal" and "Loctal" tubes were much easier to get back in the proper orientation as the center locating pin was longer than the outer electrical pins. You could get the tube center pin into the center hole of the socket pretty easily, and then carefully rotate the tube until you felt the keys align, and push down to seat the tube.

      The all-glass miniature 7-pin and 9-pin tubes could be very difficult to get in the correct orientation if you couldn't see the socket and had to do it by "Braile".

    4. At one time in the dark ages I had a 3rd Class Radiotelephone license. To my friends that made me an "expert". I always used a marker down the side of the tube and onto the chassis. Worked great putting the old tubes back in. Replacement tubes? Curses.

    5. Yeah, I had a couple of 3rd class tickets for different services. One was aircraft radio (Student Pilot), and the other was when I part-timed at a local radio station, and would have to fill-in on rare occasions. Usually just things like announcing the callsign, but I got to read the weather a few times. No "Les Nessman" hog reports, though.

      I've seen the draw-a-line technique, along with those little sticky arrow Brady markers and pieces of masking tape.

      Hey, whatever works.

  5. A pleasant new year to you and yours.

    Appreciate the link, I have a 1934 RCA that needs new tubes.

    1. Thanks, Grog.

      Tubes are pretty easy to find. If you want NOS, there's eBay. For new, there's AES and several others.

  6. You get that up and running and next we will read about is you getting a 'lectric G-tar and running off and joining a long haired boy band... Happy New Year to you sir!

  7. Nice of you to take that on. Best wishes for getting it back up to speed!

  8. Thanks, NFO! Still waiting for a few parts, like the replacement speaker and the grill cloth, but the chassis cleaned up nicely.

    Now I have to find somebody with an electric guitar so I can "test" it when it's finished.

    1. James Hetfield has a house in Colorado, not sure where, never met him, but he may help you.

    2. I think some of our extended family members here play guitars.


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