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First post ...actually need some help

Started by Planobilly, November 21, 2015, 11:03:40 PM

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My name is Billy Simmons. I am an old guy, 68, and live in Homestead Florida. I am a disabled vet from the Viet Nam police action...lol. I need to learn a new trade because social security and disability is just not enough to survive on in today's world. I am going to teach myself how to repair guitar amps, both tube and solid state plus I am already working on marine electronics to the extent I know how.

I have a bit of basic electronics knowledge. Been playing guitar and piano as a hobby most of my life and worked on my own stuff without killing myself, so far...lol  All kidding aside I understand well how to discharge a cap and the dangers involved in high voltage stuff.

I have saved up about $1500 to buy the rest of the tools I need, dummy loads, used analog scope, signal generator and a variac. I have a new Fluke 177 and two or three cheaper Extech MM's. I am currently researching what to buy on the budget. I could use a bit for feedback on the scope and signal generator issue.

I have been studying the books. The math sometimes gives me a headache. Been collecting schematics, searching for good suppliers for parts. Just got two old not working Fender amps to mess with and want some junk SS amps to learn on. Also want to build a small class A amp from scratch and some sort of solid state amp from scratch, and a fluxgate magnetometer...just kidding about the mag.

It is kinda hard to find good honest workmen for anything here in south Florida so getting work is not a big issue for me. I also don't need to make a lot of money...a couple of hundred a week would be a big help.

I need straight up advice and don't worry about being politically correct with me as I am not bothered by the truth as others may see it.

Am I missing something? Have I lost my mind to think I can do this stuff at my age?

Cheers guys,



Check out this forum also. They guys are great and you may find many useful things in the classified.

Your never too old till your dead.



J M Fahey

Suggest you search and download a copy of Jack Darr's "Servicing your guitar amplifier" , a nice vey compact capsule of general purpose knowledge as applied to this.
Then search for *commercial*  amp schematics, tubed classic Fender, Marshall and Ampeg are basically all over the place, plus a few SS Peavey/Crate/Fender/Laney/Marshall.
Get the beginner type ones (10/15/25W)  which have all the necessary building blocks (Preamp/tone control/gain/distortion/reverb/power amp, both discrete and chipamp type/power supply/maybe simple loops or switching.

Once you understand those , then largest and most complex ones are basically the same, with 2 or 3 channels instead of 1, more complex effects (if any), larger power amps, but still functionally the same.

This is one kind of shortcut pathm which will save you some time.

Get dead small amps from schools and such, no guarantee of anything, and when and if you repair a couple you re-doneta them to the school/church/whatever.

Like Doctors who work free (or for peanuts)  at some public hospital to build up (much needed) practice and eventually customers.

You might also repair some pedals, nobody wants them because an hour bench time often approaches purchase price, but it's interesting practice.

Don't invest way too much, get a cheap scope, etc.
What you need most is learning and practice and that can't be bought.


Just curious, tell me to stuff it if you like, but you were in the draft era.  I am curious  if you went in on your own, or were you snatched off the street?  Don't worry, there is no wrong answer here.

If you have a home shop, then sure, why not.  Going into a commercial store front is exceedingly hard to make profitable.  One deal that can work out well is to bargain for space in an existing music store.  Maybe nominal rent or sometimes they will give you a room just to have you there.  It is an asset to have service available at a store.  You get built in customers.  The downside is that you can't be leisurely about it.  I am in your age bracket, and I couldn't work 8 hours daily, in fact I closed my independent shop a while back.  They would expect you to be there consistently and on a schedule.

Working out of your home means you control your own hours, and you have no rent on the shop.  Many guys like that still do work for stores.  They go to the stores to pick up and drop off repairs.  Or the store comes to you.  Whatever you all agree to.

Space.  Do you have a lot?  Or a little?  Basement or ground level?  Are there even basements in Florida?  One can work in a tiny shop, but then a 32 channel mixer comes in, and there is no place left to stand.   Basement with a walk in door can be OK, but stairs are a killer.  Hauling an 85 pound SVT head down stairs is dangerous, let alone inconvenient.  Or a huge PA speaker.

You need a good bench.  If you have room for a full 4x8 sheet top, go for it.  I like mine like 3 feet deep so I can reach all the way to the back.   8feet is an OK length, due to space, mine is abut 6 feet.  But our stuff is heavy, so it needs to be sturdy.  I have always made mine.  I lay three 2x10 or 2x12 planks side by side, then screw two or three 2x4 beams crosswise onto them.  Now flip it over and you have a bench top.  I cover that with 1/4 or 3/8" plywood.  I always carpet my work surfaces so I can protect the surfaces of the customer units.  I bought some commercial legs from WW Grainger.  But you can easily bang together a base from 2x4s.  Places like Grainger sell bench tops too, I recommend solid wood.   But if you have a folding table like the school community room, that will work too, though I recommend a sheet of ply on the top to augment it.

A riser is a shelf across the bench above it.  I bought a commercial one from Grainger, but you can make one.  Mine has electrical outlets across the front of it, very convenient on an electronics bench.  By putting your scope, generator, etc up on the riser, you keep them off the bench top so you have room for amp chassis or turning them around, whatever.  I added a fluorescent up under mine.

Many guys plop whole amp right onto the bench, but I would be lost without my wheeled cart.  Like this:
I bought mine dirt cheap from another shop, but you can easily bang one together with 2x4s and a top of ply.  The wheel let me sit there and spin it around to get in the back.  Good for amps, I find it easier to check out mixers from the rear side, etc.  Also, a large item can be wheeled out of the way if I need to work on something else.  I often set a combo on the cart, pull the chassis out and swing the chassis onto my bench.

If you have a good meter, you are 90% there.  A scope is essential, but you can do a hell of a lot without one, at least to start.  There are excellent scopes on the used or ssurplus market.  I find them at the local university surplus facility all the time.  Local ham radio fests have them.  I don't trust ebay, but many are there.  If a scope works, it is probably enough scope.  For our work, there is no demand for high bandwidth.  A 100MHz scope will work great, but so would an old 10MHz scoep.  Most scopes now are dual channel (or more), but an old single channel scope will cover most of your needs.  I rarely need both channels, I use them mainly for convenience.  Point being you can find an old minimal scope for cheap, grab it.  You can learn about using a scope, and later shop for a better one when you are more settled and experienced.

Any basic continuously variable signal generator will work.  No need for fancy, unless fancy came cheap.  But we do deal with music, so have some source of it on the bench.  I have a cheap Technics stereo receiver on the bench, a line out from that is my main test signal.  A CD player would work as well.

I was a physics major in college, so I know some math, but really, most math I do here is arithmetic.  I keep a pocket calculator on the bench so I can do quick Ohm's Law calculations.  Don't sweat the math.  There are good schematic resources online, but do collect them.  I carry my collection in my pocket on a flash drive.

There are plenty of parts suppliers.  I like Mouser for general electronic parts.  Antique Electronics Supply for amp specific parts, but there are many others.  Just learn them as you go.

I MIGHT be able to help on some shop stuf.  I closed my shop and am liquidating my stuff.  I know there is a variac or two available, and some other things, send me a PM if you are interested.

I see Juan has posted as I wrote this, listen to him too, he knows what he is talking about.


As an old retired tech I can vouch that both JMF and Enzo are professional techs giving good advice.   :dbtu:

You gotta have a good workspace (pref ground level unless you are pone to flooding) and a big bench with good lighting, I'll suggest LED these days over the traditional fluro.  Once you get going, start small, distribute your card to local music shops.

And have a go - collect some junker dead amps, from wherever (thrift shops etc) and try to repair.  Build your Class-A amp.  The math is valuable but it's a support to understanding - a circuit is what it is.

Buy tools and instruments as needed.  They make it easier, but in many cases a lot of diagnostics and even repair can be done by careful observation.  The vast majority of problems are physical rather than electronic, dirty pots, dirty sockets or wrenched solder joints on them, &c.

Guitar amps tend to be simpler than most electronics (unlike, say, a marine radar).  The signal goes in here, through there and there, and comes out over there; and if it doesn't it's a bit like plumbing, where's the blockage?

Be orderly and methodical, know when you are out of your depth (a lot initially) and be like a few of the other guys around here and ask for help.  No shame, none of us were born knowing.

All the best in your venture, age alone is no impediment.   :dbtu:

ps - you'll find Jack Darr on my site here;
If you say theory and practice don't agree you haven't applied enough theory.