Want to build an amp, any advice?

[PartsTele101]

I recently replaced some tubes on my 76 Fender Champ, and decided to go ahead and peek inside it. So, I pulled the chassis out and saw that it was extremely simple. It doesn't seem like it would be all that difficult to build my own.
Does anyone have any advice as to building amps?
Should I just use mine as a guide and replicate it?
And lastly, where do I get the parts? (radio shack, mouser, grainger, fry's, etc...)

[T-Bird]

Hi.

First of all welcome to TalkBass.

Secondly, You do know the safety procedures around tube amps, bleeding capacitors, dealing with high voltages etc.?

If You do, fine.

A good place to start IMHO would be the AX84 project page http://www.AX84.com/ or www.hoffmanamps.com.

Most of those circuits on the AX84 page are Champ based or inspired.

Regards
Sam

[PartsTele101]

I am familiar with safety precautions as I have been working with electronics for about eight years.
I will look at those suggestions. Thank you.

[T-Bird]

Hi.

You're welcome.

I just wanted to make sure, once I gave a person quite through explanation of a diagnostics procedure and then he asked "what is a PCB". Shivers ran down my spine.

Regards
Sam

[JayM]

This page has tons of downloads with old tube amp designs:

http://www.pmillett.com/technical_books_online.htm

Parts-wise, you might have better luck in the amps forum.

[PartsTele101]

I know this is a little off-topic, but I didn't want to start another thread. My problem is that my Champ hums. Not terribly, but pretty bad. The hum increases with the volume and is just bad enough that I wont use my champ for recording. All of the tubes are original, but very lightly used. Any help?

[T-Bird]

Hi.

First the source of the hum has to be determined.

Starting with the assumptions that the Champ in question:

#1 Is grounded properly.
#2 Has its original guts, IOW hasn't been modified.
#3 Has the original AC filament supply, without hum balance pot.
#4 Has the original PS caps.
#5 Has the tube rectifier.



#1 If the grounding is faulty You'll get hum, a bit or lots depending of the situation.

#2 Any unprofessional modding tends to leave the wires inside the chassis untwisted and in a mess. Tube amps generally require a neat, well thought wiring harnesses to be reasonably quiet.

#3 Modding AC to DC usually reduces hum, but might change the sound. You can also put a hum balance pot there.

#4 By now the caps are most likely at the end of their journey, replacing all the electrolytics will reduce hum, will also change the sound but usually NOT in a bad way .

#5 Being tubes, tube rectifiers will induce some hum and as in a single ended design the PSU sag is constant and therefore won't change the dynamics as much as with PP, most of the people use the SS module.



Chopsticking may help with the wiring issues, and in this stage the knowledge and application of electrical safety procedures come in handy.

It's best to try one change at a time, in order to be able to find out what caused the hum in the first place.

Regards
Sam

[TheoFly]

Originally Posted by T-Bird

Hi.


Chopsticking may help with the wiring issues, and in this stage the knowledge and application of electrical safety procedures come in handy.

Sam .... what is Chopsticking? Haven't heard that term used in this context before.

[T-Bird]

Hi, Theo.

Chopsticking is a diagnostics procedure where You have a live amp and a NON conductive poker to tap the components to find the faulty one, or move/separate the wires to find out if the interference can be minimized or totally eliminated.
Best to do that with one hand in the pocket, like any other hi-voltage probing .

Don't know if chopsticking is an official name for it, but that's what it's called in several DIY electronics forums that I visit, haven't seen it used in print though.

Regards
Sam

[JohnnyPustular]

A great way to learn how to build amps is to attend one of the Egnator workshops. They provide all the tools and parts to build an Egnator head (an awesome guitar tube amp) and two days of instruction while you build. Its pricey, but you leave with a head that is worth more than you pay for the workshop (at least it used to be) and great information about the compromises and options in amp building.

[PartsTele101]

In response to T-Bird...
Ok, this is what I know. All of it is original, and there are no grounding problems.
I've never worked on anything with tubes, so #5 is Greek to me. I like 3 and 4. However, I don't want to change the sound at all.
Its been pretty lightly used, so the caps should be fine... Right?

[T-Bird]

Hi.

#5: http://www.groovetubes.com/GT-SS-5AR...ate)_P1647.cfm

All the mods done to any amps should be fully reversible, so there's really no harm in trying if the amp in question doesn't meet Your hum requirements at the moment.

It's not the use, it's the lack of use and the age of the electrolytic capacitors that makes them bad. I've had unused NOS caps turn out bad out of the box.

Also, a vari-AC should always be used when firing up unused or lenghtly hibernated caps.
The sudden voltage spike can render them useless.

Regards
Sam

[TheoFly]

Originally Posted by T-Bird

Chopsticking is a diagnostics procedure where You have a live amp and a NON conductive poker to tap the components to find the faulty one, or move/separate the wires to find out if the interference can be minimized or totally eliminated.

Ah .... very good. I will have to remember that. I've been working on electronic stuff since I was a 12 year ham operator and I haven't heard that before. It sounds like a much more elegant description of the technique than "whack it with a stick", which is what it was called by the grizzled old TV repairman that first demonstrated it to me as a kid!