Getting into Amp building/modding

magikker · Post by **magikker** » 27 Jul 2007, 21:03

Effects don't scare me. I'll take apart or put together just about anything anyone will throw my way. However, I've never messed with the inside of an amp. This is mainly because of all the "It could kill you!!!!" stuff I hear.

The more I am getting into build pedals. The more I think I might like to make or mod an amp. Now, my question is what would be the best "First Project" for someone that doesn't want to die?

vanessa · Post by **vanessa** » 27 Jul 2007, 21:38

magikker wrote:Effects don't scare me. I'll take apart or put together just about anything anyone will throw my way. However, I've never messed with the inside of an amp. This is mainly because of all the "It could kill you!!!!" stuff I hear.

The more I am getting into build pedals. The more I think I might like to make or mod an amp. Now, my question is what would be the best "First Project" for someone that doesn't want to die?

I think you might really enjoy building a simple Fender Champ or Princeton. You could build one into a large stompbox enclosure (I've seen people do it) and use it as sort of a home use head to a speaker cab. Later you could build it into a combo or a head box of it's own. (Or you could purchase a whole kit)
Another that would be a good home and gig amp would be a 18W Marshall. Lots of information, easy to build, and fantastic tone (lots of kits out there).

Oops, I forgot. Most guitar amps use AC current as apposed to stompboxes that use DC current. They all can kill you. You have to be careful and learn how to discharge the filter caps before you can proceed to work on them.

bajaman · Post by **bajaman** » 27 Jul 2007, 23:34

ALWAYS place a 220k 1 watt resistor in parallel across the main electrolytic filter capacitors in a vacuum tube amplifier power supply.
That way, when the amp is switched off, after a few minutes the high voltage present will drain away to earth.

ANOTHER good idea when working on high voltage supplies is - do not touch the grounded chassis and the positive terminal of the high voltage electros at the same time - DUH

FINALLY, do not use your expensive Fluke multimeter set to ohms range for measuring high voltage in tube amps

Cheers
bajaman

bajaman · Post by **bajaman** » 27 Jul 2007, 23:36

ps: I have never been killed working on valve amps - and I have had a few shocks - just makes your heart beat a bit faster

invictus · Post by **invictus** » 28 Jul 2007, 00:52

this reminds me of my father... he says that a slight jolts of electricity is good for his arthritis...

theblackman · Post by **theblackman** » 28 Jul 2007, 04:36

bajaman wrote:ps: I have never been killed working on valve amps - and I have had a few shocks - just makes your heart beat a bit faster

haha
i have never been killed also and that makes me happy!

also isn't one of the safety tips for working on high voltage equipment to only use one hand at a time and use an armband on that hand connected to groun d? would that stop the electricity from going through your heart and killing you?

soulsonic · Post by **soulsonic** » 28 Jul 2007, 10:07

I've never been shocked working on a tube amp... but I HAVE been shocked working on a solid state amp. It funny because the caps in a tube amp usually discharge pretty rapidly, but in when you're dealing with a solid state amp with 10,000uF of capacitance it's a different matter. The solid state amp that shocked me wasn't enough to really damage me, but it was a pretty annoying painful tingle.

The most important thing to help you keep safe while working on an amp is to know where the high voltage is at, so you know what points to avoid touching while working on it. Just take care not to come in contact with those parts and you should be fine. If you have to take high voltage measurements, it's a good idea to clip the leads in place before powering the amp up so you don't have to reach inside it while it's live. If I have to probe at a dangerous voltage point, I always try to keep one hand behind my back. And another important thing; take your rings off. A metal ring on your finger is nice convenient thing for high voltage to touch and shock you, taking them off makes it that much harder for something to reach out and touch you. It's a good idea to remove pretty much any metallic jewelery that might accidentally come in contact with something in the amp.

bajaman · Post by **bajaman** » 28 Jul 2007, 10:56

another piece of advice - unplug the power cord from the mains supply

before working on any mains equipment

I speak from experience (or lack of) here

bajaman

JHS · Post by **JHS** » 28 Jul 2007, 13:03

You can mod any amp to your liking, it doesn't matter if it's a small or big mod, but if an amp don't sound good stock it won't sound good or better after the mod.

I think it's not worth modding old amps, a good pedal in front of it will make it sound like a modded amp and often it's the cheaper solution compared to modding.

IMHO replacing the tubes and filter caps and some worn resistors is the best "modding" for any older amp.

JHS

KippeKiller · Post by **KippeKiller** » 18 Aug 2007, 14:32

Maybe a good starting point is one of those cheap single ended, low watt tube amps offered by several big musicstores on the web.
Here in europe there are some Gibson GA-5 clones for about a hundred euros on the market.
They won't sound extraordinary good (perhaps "special") but they are pretty simple in design, layout and function, so its a good start to see what is happening in there, and with the right portion of respect towards the HT inside and the above mentioned tips it won't kill you unless you want it to.

regards

Mathias

Post by **modman** » 18 Aug 2007, 17:05

http://www.angela.com/catalog/how-to/single_6v6/

Really struck a note with me long ago already -- haven't found the time yet... but really should do this one.

DougH · Post by **DougH** » 20 Aug 2007, 17:18

The best place to learn about building amps on the internet is ax84.com. Good projects for all skill levels that sound good, and a great support network in the forum. You can't go wrong there.

vanessa · Post by **vanessa** » 20 Aug 2007, 17:33

modman wrote:http://www.angela.com/catalog/how-to/single_6v6/

Really struck a note with me long ago already -- haven't found the time yet... but really should do this one.

I've seen that one. I might build that one someday soon. Right now I'm looking at a 36W Marshall (18W x 2) with a half power mod for 18W.

call1800ksmyazz · Post by **call1800ksmyazz** » 20 Aug 2007, 19:01

bajaman wrote:another piece of advice - unplug the power cord from the mains supply before working on any mains equipment
I speak from experience (or lack of) here
bajaman

100% right here. I accidently leaned on the power plug while it was plugged in on my last amp build

. You may think that its impossible to accidently just lean on that, but its not!

And also with the multimeter statement: Be careful measuring the outlet wall voltage while the multimeter is set for DC! I did this the same day as my power plug incedent and blew the power breaker in my garage and there was a huge spark. Heres some picture of what happened to the power plug and the multimeter probes!:

Kerry

tonator · Post by **tonator** » 03 Sep 2007, 06:10

Also, the KT66 (Champ-type amp) at tubetown (German site) is a good starter. Or the french G5 project. AX84 is great, of course.

I think the two things you have to consider when working on tube amps is, 1. unplug the power cord (understood), and 2., always decharge the big filter capacitors before touching anything inside.

petemoore · Post by **petemoore** » 12 Sep 2007, 22:09

Test for very low voltage and leave the drain resistor on while working on the amp.
I wrap the drain resistor in electrical tape because it starts smoke warning of excess drain resistor heat if I plug the amp in and leave the drain resistor connected [not recommended/not bad].
But I clip that drain resistor right to the on switch, and routinely disconnect power first thing before touching anything else, I have the resistor hook ended, and a place that grabs it's wire makes that connection, then I test with the DMM and watch it go below 30vdc....20vdc...0VDc, then I think about working on it.
First eliminate anything 'less than known as beefy', which means at least caps on 'old' amps, spare tubes.
Unless something jumps out at you as 'wrong' [...say.. excessive bass] try outside fixes and experiments outside the amp, @9v or at the speaker for getting it to respond 'more-how'.
Make an amp jig for working inside upside down chassis, supporting the chassis with good footing, prevents pressing/breaking tubes, a 'u' shaped affair, re-inforced wood...I have an old amp cabinet top and 2sides, happens to fit.
Right now I'm looking at a 36W Marshall (18W x 2) with a half power mod for 18W.
That oughtta be a 'nice one two'!!
I could never get the big tube amps to distort, what's the use? ..about as useful as an tube amp that doesn't get loud enough.
Sometimes I wish I had 1/2 that, so I defeat ~1 tube to run @ between 7.5w - 15w.
seems like it takes about 15w to actually get a 12'' working good, which for me is basically way too louder than it needs to be unless it's around other amps/drums.
anyway, worth thinking about getting the headroom down to where you can easily find it, that's where all the loading is = reason for having a guitar tube amp is so it'll distort some.

TragicTravisty · Post by **TragicTravisty** » 31 Aug 2008, 04:49

noob question: can i discharge power supply caps by shorting them out?

marshmellow · Post by **marshmellow** » 31 Aug 2008, 09:27

Sure you can - but it's not really the recommended way

. In short: please don't do it. Causes nice looking but dangerous sparks und will damage the capacitor.

Normally you would either install a bleeder resistor (220k / 2W or something like this) in parallel to your high voltage elkos and wait after you switched off the amp until they are not loaded anymore (measure!).
Or you use a smaller resistor (1k / 10W, doesn't take that long to wait while holding), solder leads with alligator clips or measurement tips to the ends and unload them manually.

TragicTravisty · Post by **TragicTravisty** » 31 Aug 2008, 14:32

so im assuming that they are not constantly installed, only temporarily so when its open?

marshmellow · Post by **marshmellow** » 01 Sep 2008, 07:52

You can leave the bigger bleeder resistor (~220k) in the circuit, no problem with that. That is the way most people do it that build amps I think. It is trouble free and you don't have to remember to put it in or take it out.

The smaller one you have to remove before you switch the amp on, that's why there are alligator clips. Oh, and isolate everything with shrinking tube on that resistor/lead soldering. You never know where you might touch it unconsciously.