Complete newbie to amp repair

[MartiniShakers]

I recently acquired a '79 Vibro Champ. I love small tube amps, and this one has great tone---at love volumes. Anything above, say 4, and total breakup on the bass notes. Not good tube breakup--broken speaker type fuzzy crap!
I plugged a 2x12 cab (8 ohm, I know is bad for a 3.2 ohm amp, but it was only plugged in for about 30 seconds).
Same nasty breakup above 4 on the bass notes. Muddy crap.
I know this amp is capable of great clean Fender heaven.
I was going to take it to a local amp tech who was going to charge me around $120 to replace the caps, and generally tune it up.
Then it occurred to me---Why don't I learn to service tube amps myself, being that I play them and all. Might be a useful thing to learn.
Here are my questions:
1) What is causing the bass notes to mush up like that?
2) How hard is it to service tube amps for someone with no knowledge of such things? I have very crude soldering skills.
3) How hard is it to learn to work on them, what is the best resource for said learning and how long does it take to become semi-proficient.

I figure I have a free amp, and it is the perfect place to start.
Any/all advice would be nice!
Jory Lee-The Martini Shakers
Martini Shakers on MySpace Music - Free Streaming MP3s, Pictures & Music Downloads

[MartiniShakers]

I also forgot to mention that it makes an audible hum--with or without a guitar plugged in.
Jory Lee

[MartiniShakers]

Also, it's a '78.

[R.G.]

2) How hard is it to service tube amps for someone with no knowledge of such things? I have very crude soldering skills.
3) How hard is it to learn to work on them, what is the best resource for said learning and how long does it take to become semi-proficient.

You go guy. After all this isn't rocket surgery. And it's not dangerous at all.

Oh, wait! It is dangerous. You could touch the wrong thing and die.

1. Crude soldering skills won't be enough. You need to be good. This isn't hard, but like music, you have to practice.
2. You need to know some electronics. It's some learning that you'll have to pay for, either with money and time, or sweat and time, or both.
3. If you have enough drive to do the learning, you can be OK at simple internal repairs (that is, more complicated than replacing fuses and tubes) in about a year if you work hard at it and have a skilled teacher. To be really proficient takes longer. Apprenticing to a working amp tech is a good way.

How hard that is and how long it takes really depends on how much you like the work and how hard you study/practice. This is not the same as saying you're not smart enough. I'm smarter than a lot of guitar players, but I don't practice enough, and even if I did, they have something perhaps best described as talent that I will never have. I'm a technician, not an artist at heart.

Some people are artists and not technicians. You can learn techie stuff, but you have to have enough tech talent and desire to want to do it. I know guys with EE degrees that could not design a decent length of copper wire. They forced themselves through the formal training then promptly discovered they didn't like it.

[MartiniShakers]

I'm a service tech for DirecTV. I really enjoy the work, and it has me thinking that I could, perhaps, learn to work on my own amps.
I really enjoy working with my hands, and would love to know how to repair/mod my amps.
How can I learn to solder? I have a ton of old radios and record players around that need help. Could i start on those and work my way up?
I love guitar. I want the stuff i play to sound like it does in my head.
Unfortunately, I've never had the resources to purchase the Twins and other vintage Fender amps that I've wanted. I've always had to make do with the cheapest stuff available.
I was so happy when the Champion 600 reissue came out, because for the first time since my old Silverface Bassman 60 watt, I could afford an all tube amp.
5 watts yes, but I play Rockabilly, and mic'd up, it sounded HUGE!!!
Then I got a Super Champ XD. WONDERFUL!!! I've played a ton of shows with it!
Then, a customer of mine (I'm a service tech for DirecTV, remember) gave me a '78 Vibro Champ for free!!! I was so excited I almost cried!
Vintage tubes!!! RAWK!
I got it home and it sounded great at low volumes.....
I want more, and I think I have the patience/smarts to figure this thing out.
I hope that gives y'all a bit more insight to my motivation!
Jory Lee
P.S. If any of y'all want to tackle my amp for me, I'd pay shipping+parts+labor if you can do better than my local guy. I'd rather y'all do it...

[Enzo]

I just have to ask, is your music...stirring...?

(thank you, thank you, I'll be here all week.)



if you are a service tech at most anything, then you have to learn or have already learned the universal skill of troubleshooting. That is the systematic process to isolate the problem.

perhaps you know how to wield a meter, and better yet, undertand what the readings mean.

As RG pointed out, the voltages in a tube amp can KILL YOU, rather unlike circuits running on 5 and 12 volts. If you respect that and work safely you will be OK.

RG his own self has a web site, Geofex, and a dandy tube amp debugging page.

You have taken the first step, trying a different speaker. The symptom remains, so the speaker is not the issue.

Have you tried different tubes in the amp?

At 30 years old, I don;t doubt your caps are tired. probably all new ones are needed.

Certainly you can practice solder work on old stuff. And if it is stuff not intended to be fixed, then you can hardly screw it up, right? Sometimes I hand out an old dead circuit board to someone wanting to learn to solder...........

[Chuck H]

Jory,
You've recieved replies from two of the most respected and experienced posters on this forum. Listen to what they have to say. And...

Most of us got started with this stuff the same way. In my case I had an amp tech who ran out of time to cater to my perfectionism. And let me be clear. He started a second business and actually ran out of time. Prior to that I think he saw me as a quirky challenge So I decided to start learning this stuff for myself. That was about seventeen years ago. I ended up with a passion for designing (I actually don't like the building part of it much, but it's the only way to realize a design). I started with mods. And that can be fairly simple. designing a complete amplifier requires more polish and refinement that you only get from experience. There have been posters with much less aptitude than yourself who ask questions like 'How do I design an amp?'. To come out of the gate with that goal is unreasonable. But you just want to be able to take care of your amp and perhaps tweak it enough to stop it from farting out Good place to start.

The best advice I can give is: learn the anatomy of tube guitar amps. That is, learn how to recognize a "resistor" or "capacitor" on a schematic and what their basic functions are. Learn to recognize on a schematic what part of a tube diagram is the 'cathode', the 'plate' and the 'grid'. Once you understand what the basic components do and where they are used on a tube you will start to understand why. Stick to voicing and gain within the signal path at first. That'll be pretty easy and you'll be revoicing your your Vibro Champ so it won't fart out in no time.

Analagous to that is basic tube amp service. There are parts in tube amps that wear out with age (actually all of them, but) electrolytic capacitors and tubes are most succeptible. Basic tube amp service is a subject that is covered add nausium on the web so a little searching will do you right.

Above everything is safety. There ARE lethal voltages even in your little five (actually three) watt amp. Tube amp service safety is also covered all over the web. Search and learn this stuff first. You will learn how to bleed voltage off the circuit to render it safe to work on. You will learn basic techniques that will keep you from harm. If your interested in a new avocation I have to assume that means your not interested in dying. No $h!t. Learn the safety end first.

Once you learn how to identify the different parts of a tube and the basic function of resistors and capacitors you will be able to post competent questions and possibly even understand the answers.

It's my opinion that your VC needs service and perhaps a little revoicing for how you play. Learn the basics, service the amp so it's running up to snuff and if it still isn't performing almost anyone here can give you tips on revoicing it. And you will have learned a great deal and be better able to understand the "why" in the changes by this time.

Chuck

[User Name]

hey jory,

good to see your interest in the diy scene.

i have been in electronics since '90 and have built a lot and have repaired a lot of circuits and i sometimes think i may know as much as some people on this site as well as others have probably forgotten.

my expertise is in repair and not so much design, so in regards to theory and formulas, i pretty much know where to find and use the info, i just don't have it memorized. i am sure there are many here as well as on other sites that would be happy to help.

one of the biggest things that i can tell you is this:

electricity will kill.

in light of that, be very careful when looking around. i've been bitten more times than i can remember, which is maybe why i can't remember....lol.

in any case, i can recommend a book that would be a good starting point. i am sure there are plenty of other books out there, that others can suggest.

"how to repair old-time radios" by "clayton l. hallmark"

outside the rf/if sections of a tube radio, the rest is basically the same as an amp, but in most cases, lower voltages.

anyways, that is about all i can suggest.

OH!!! one other thing, if you decide to tackle this and start working on tube equipment, invest in two things that can be had for relatively low prices: a variac, and an isolation transformer.

variacs are great for bringing up an amp/radio (tube or solid state), up to working voltages. in most cases, tube type equipment will begin to operate at about 45% input line voltage.

an isolation transformer keeps the uut, (unit under test), isolated from the mains voltages from the wall, meaning, safer for you!

ok, i think that is all i have to add.

bill.

[MartiniShakers]

The amp is just too nice to monkey with on my first attempt.
I think I'll start with one of the dozen or so tube radios that I have that don;t work.
I'm sure there are some principles of both that are the same, and I can at least practice soldering on something that I won't cry about if I ruin.
Amp is in the shop with qualified amp tech.
Any advice on a decent quality soldering iron that won't break the bank?

[gbono]

Soldering is like welding you get better with practice. You must also learn how to de-solder connections too. I'd start by building my own guitar cables and move on from there.

Check some of the old posts for reference books - must have to self teach yourself.

Also seek out electronics salvage (now known a recycling) stores in you area and ham swap meets, etc. These are good sources for obsolete parts and "networking".

Don't limit youself to only tube designs.

[MartiniShakers]

I'm only focusing on tube stuff now because that's what I play, but I did have a soldering emergency while playing an out of state show.
My wireless unit's antenna broke off, and we had to book it to a Radio Shack and get a $7.00 iron that came with solder and everything.
It looked like crap, but got me through the show.
I've been watching some videos online, and actually repaired a broken mic cable this morning!
It also looked like crap, but it's a start!