Heathkit

[Enzo]

As I write, there are TWO Heatkit TA-17 guitar amps sitting next to me. What are the odds? One came over from a dealer, and the other is from my warehouse.

The one from the dealer turned out pretty nice - looks good and the kit was neatly built back when. And all of it works now. I had to do a bunch of small things to it, noisy resistors and noisy transistors and leaky caps. The one I have was not built so nice and isn;t quite as pretty. But having fixed up the other one, I was inspired to dig mine out and rebuild it.

The amp wouldn;t be my choice for playing through, but the mic channel is strong and clean. The guitar channel, well, it is what it is.

[schraedertr]

I don't have a warehouse, being an amatuer repairer, I have a garage stall with "deffered projects". I've been curious to what other's success rates are.

My projects mostly come from a catalog sales outlet and can be anything from major shipping damage to an unplugged cable to user damage. I try to avoid some categories, and I do sometimes buy a combo amp for its speaker. But sometimes I get a pallet of mixed stuff and you take the bad with the good. I just reviewed the last five years of data, and I've been running about 70% success on amps on good years.

I know everyone would like to be able to fix 100% of everything that comes in the door, but how do you decide what to turn down on sight and what to tackle?

[Enzo]

I'd see a difference between items customers present for service and fixing up stuff on my own. If it is my stuff, I am fixing it either to sell, or to own, or in some cases just to see it do its thing. But the customer is going to pay me and expect a working thing in return.

Most repairs are simple. I don;t need special resources to fix a broken jack or control, and transistors are eternal. I look at potential repairs with parts in mind - for example I might have a hard time finding a motor for a strobe tuner. I also look at the amount of work and what that labor would cost. I can't really expect a customer to pay me three hours labor at $60 each to rebuild a little Crate practice amp that turned its board to charcoal.

I can fix a lot of stuff without schematics, largely because under the skin, most circuits are alike. But in some involved circuit, if I can;t find schematics I may not be able to proceed. This is rare. SOmetimes a part is just not available - at least not at a reasonable price. The SAD1024 IC from a delay pedal for example.

In those cases, I tell the customer I can;t repair their thing within its value, or that I simply cannot get what it needs. My shop, unlike many, does not charge for the initial once over inspection. SO I can hand the thing back and say "no charge." to a smiling customer.

In the case of my stuff, if it is something I want to own and use, then I can decide if what I'd have to put into it is warranted. WHy spend an hour and a half rebuilding burnt off pc board traces on an amp I can buy used for $40? If it is something I might potentially sell, I have to consider what I might get for it. I have a little solid state Bogen something here next to me. It blows fuses and has one control snapped off. I could rebuild the power stage with $10-15 in parts, and maybe up to an hour of my time, and then what? I have an amp I might get $30 for on ebay. WHy bother. It is no challenge, just a dumb repair. The only reason I don;t pitch it is that it is the perfect size for a footrest next to the bench.

At this point in my life I am fairly confident I can fix anything that comes my way. So I do appreciate a challenging repair from time to time. It wasn;t difficult, but I really enjoyed when the guy brought me a Conn DYnalevel. (Do a search here, I described it with photos a while back) SO I might fix something just to say I can. Or just because I really want to see it working - like the DYnalevel. or the Heathkit.

ANd I might add, that is part of the fun of posting here, when I can help someone sort through a complicated circuit like some CArver amp.

The first thing I asked Mike when he dropped off the Heathkit from the dealer was what can you sell this amp for and what can you afford for repair? I would up doing a lot of work that I didn;t bill out, just because I enjoyed working on something really different.

[guitaraddict]

my fun

I hope I speak for many of us Enzo when I say the fun for me is reading your post and that yourself and many others here have inspired me to step a little ways out of my comfort zone and take on some of these challenges.(keeping in mind the safety net this site gives me). My better-half thinks some of my stuff is junk but to me its a learning experience, a relaxing moment, or a few bucks for the next project just waiting to happen.

[Enzo]

If you or anyone else gets anything from the stuff I write, I really hope it is an understanding of HOW to troubleshoot circuits. A systematic approach to localizing the problem.

It saddens me a little when I hear, "MY amp does this or that, what is the bad part?" Or "Do you know how to work on Fenders? (or Peaveys, or Mesas, or whatever)" The question should be how do I FIND the bad part. In whatever I have. Troubleshooting is a universal skill, it applies to everything we see. I don;t approach something on the basis of its brand. Determining if an output tube is bad doesn;t depend on it being a 6L6 or EL34.

Think about cars. You learn to drive CARS, you don;t learn to drive Chevys. No one would ask, "Do you know how to drive a Toyota?"

I have an ongoing debate with a friend over tube amps. I claim they are all the same, he maintains they are all very different. He is talking about the sound and dynamics, I am talking about the circuits. If I encounter a problem amp, I will check for B+, make sure the screen resistors are not burnt open, check for bias supply. I might look for signal on the grids, etc. Nowhere did I mention what brand or model, it doesn't matter. The details differ, sure 500v on this amp, and 360v on that. Different pins on 6L6 compared to EL84, sure. But those are indeed jusy details.

SO do please get outside your comfort zone, and apply your knowledge of circuits. Once you know what a cathode bypass cap does on one amp, you know what it does anywhere.

Gerald Webber irritates me in his books when he describes some modification. He shows a picture of the board and says move this component here and change that component there. He doesn't tell you a gaddam thing about what you did or why it works, so you knw that if you make the changes in the pictures, your amp will sound different. You learned nothing. You might want to make the exact same CIRCUIT changes in another model, but you can;t because the parts are in different locations. If instead you had learned to change the plate resistor in the first stage, and the cathode bypass cap in the second, you could do that change in any amp you saw. Gerald has some interesting ideas - and some bullshit - but that aspect bugs me.

Junk? No, junk is a Hugh Grant movie. A cheap practice amp at least makes music when you are done, however poorly. I happen to like cheap junky amps. I am tickled pink to find an old Kmart guitar amp. How many guys rebuild old SIlvertone amps? Tons. They really are not very good amps. I love them.

SOme cheap Crate practice amp might be junk, but working on it is just as valid as any other amp. it has a preamp and a power amp and a power supply. it has a circuit, it has signal flow. Go for it.

[schraedertr]

I agree the troubleshooting skill set is universal, and I rarely start with a schematic. Not only is an amp an amp, but so many of them are built in places where the name goes on last. The most expensive part of many small amps is the logo on the grill.

Someone's first amp is special to them even if it is a 15W solid state, they learned to make their sound with it.

I'm sitting right next to my Silvertone 1484 tube amp that came from an Omaha pawnshop in 1971 or 72. It spent almost thirty years being shuffled from place to place dead after a TV repair shop replaced the output tranformer wrong. It's not a Marshall or Matchless, but I've still got my first guitar and amp,and if I look long enough, I can probably find a curly guitar cable.

Sometimes I do need a clue (or a schematic) and this forum is excellent for that. Among the things I've (re-)learned:
They made it that way for a reason, think about it before cursing the designer.
Always check the power supply.
Tubes are analog, they're not just good and bad, some are pretty good and some are too bad for certain locations.
Be prepared to minimize any new damage during the repair (use a Variac, or a current limiter).
Resisters usually burn up because something else is bad, find the real cause.

Anyway, thanks Enzo, and all the other senior members.

[52 Bill]

Like eating food placed in front of me, I'll have a go at anything that's put on the bench.

I agree with Enzo in that not all things should be repaired, but if someone wants it fixed I'll try and fix it, even if it means building or rebuilding a part that no longer exists.

I have one of those Heathkits around here not because it's a great amp, but frankly because it has a weird output circuit that I wanted to learn about. Sometimes it's all about learning, sometimes it's about teaching.

And Tom, Vox is selling curly cords again. Better get one before they sell out.