beginner questions

[lespaulplayer]

Hey all. I'm thinking about building my own tube amp from a kit. I am wanting to build a Marshall 2550 clone. I am really good with a soldering iron and I know how to read schematics. I know what all the individual parts are in an amp and what they do. I already know a little bit about amp maintenance, like how to tighten tube sockets, bias, ect. I have a weber bias rite and have biased quite a few different makes amps. I am always careful to never touch anything underneath the chassis when I bias an amp. I have been soaking in as much information as I can about maintenance and the building of tube amps, but I am finding a lot of the books very limiting with the information that they give. They tell you what things need to be done, but then leave out how to safely and properly do them.

What is a good dvd or book that tells you tips on repairs or building an amp? So far, everything I've read about in books, like draining filter caps and stuff like that, always says it's best left to a professional. It’s like, that’s the whole reason I bought the books in the first place is to learn the safe and proper way of doing things! It's like they try to scare you away from doing your own maintenance or building your own amps. From surfing the web, I have seen a few different ways on draining caps and was wondering which way you guys think is best? There are some things that I'm still a little confused on. Like when you have the amp unplugged and put the standby switch on the on position, that helps drain the caps. But that doesn't drain them completely right? Do you still have to do the alligator clip thing with the 470 ohm resistor in between the two clips? I have also heard that you can take an insolated screwdriver and just touch both the positive and negative ends together. That way doesn’t sound too safe to me though. I just want to make sure I understand how to drain an amps stored power safely before I go sticking my hands in one. Sorry if my questions seem stupid, but I am a complete noob at this, and would really like to get into the hobby of amp building and repair work. Everyone has to start somewhere right?

[DonMoose]

Check the filter caps with a meter on DC volts - the only way to be sure.

The reason for the warning is that there are genuinely lethal voltages inside a running tube amp, and this is the land of the personal injury lawyer.

There's a really good site that walks you through the debug process - http://www.geofex.com/ampdbug/ampdebug.htm - note the link to the safety warning and disclaimer.

Hope this helps!

[lespaulplayer]

Cool man, thanks! That page should come in handy, looks like there is a lot of useful information there.

[gahult]

Like when you have the amp unplugged and put the standby switch on the on position, that helps drain the caps. But that doesn't drain them completely right?

No, the caps will not drain themselves in standby. If there is no bleeder resistor they will not drain at all and may stay charged for a long time. Months+++ I've scavenged parts from old TV's, etc. And you would be surprised (sometimes not pleasantly) that there are caps in there still charged.

Even with a bleeder resistor installed it may not discharge the entire cap stack as in the Trainwrecks where the standby switch, when open, isolates part of the cap stack so it doesn't drain.

It is best to drain the cap stack (after you unplug from the wall) with a discharge tool and check the caps with a voltmeter to be sure. I made one like this and it works fine.

https://amptechtools.powweb.com/stick.htm

Don't discharge them with a screwdriver unless you like to see sparks and are not jumpy when you get a firecracker pop.

Always unplug from the wall and double check all the caps for zero voltage. Oh, and keep one hand in your pocket as you may not realize what you're contacting with the hand not in use.

Gary

[Structo]

With the amp unplugged, I like to use a short jumper with insulated alligator clips on each end.

Clip one end on the plate resistor of V1 (Pin 1 or 6 on a 12a*7) and the other end to chassis ground.
Flip the standby switch to play if you are not familiar with the layout to ensure the whole filter supply discharges.

Depending on the amp this could take 30 seconds to a couple minutes but generally it' safe in under a minute.

As mentioned, always measure the voltage on the filter caps to be sure.

I don't like it when somebody says to strum a chord and turn the amp power off, leaving the standby on play.

That is not a sure fire way to discharge caps and can give a false sense of safety.

Screw drivers are ok if you want to arc weld.........not.

So first piece of equipment would be a good Digital Multimeter.
Most agree that Fluke makes the best.
I have a Meterman DVM that is equal in quality.

Anyway, a good book for you to pickup would be Dave Hunter's Guitar Amplifier Handbook
It explains the various stages of common amplifiers and it does a good job of detailing things but not so complex that a beginner can't understand.
http://www.amazon.com/Guitar-Amplifier- ... 087930863X

He even includes a simple amp you can build.

[lespaulplayer]

Thanks for all the replies guys, everyone seems very helpful on this board. I really appreciate all the help.

Structo, I have heard of the way you are describing to drain the caps, but I heard that may not work on all amps? I've also heard of using the alligator clips with a resistor wired in the middle. Kind of like that thing Gary posted a link of. You hook one end up to the chassis and the other end to a positive side of the cap. I knew that screwdriver way sounded like a bad idea . Looks like I need to invest in a good digital multimeter. That was actually going to be one of the things I purchased before I buy the amp kit i want, it's the only way I'll know if I've drained the caps all the way. Oh, and thanks for the book suggestion, but I already have that book on tube amps. It is a really good book. I learned a lot from reading that book.

[Structo]

Well just about any amp with a preamp will have plate load resistors which are tied back to a node on the power supply filter.
I suppose there might be an oddball amp out there it won't work for.
Just like anything if you become familiar with your amp, you will know the right way to go about it.
Take my Brown Note D'Lite amp for example.
It has what are called balancing or equalizing resistors on the first two caps.
These double as bleeder resistors. That amp will bleed down on it's on to a safe level in under a minute.

But you can't always depend on that.
Once you become more familiar with the various types of amps, it will become clear the best way to drain the caps.

Really if you look out what's being built nowadays, as far as most boutique turret or eyelet board type amps ( not true point to point) most fall into the Fender style or Marshall style of build.

So for you, you should first learn how to properly use the meter, familiarize yourself with the various components used in amps, but nothing will teach you as much as building your own amp.
Because with every little problem you solve while building it, you will learn something.

Also if you're into it, read as many posts here as you can. These guys really know their stuff and there are several commercial builders that hang here so you have that too.

Depending on which way your tastes run, if I was you I would build either an 18 watt Marshall or a Fender 5E3 Deluxe.
Both pump out enough power to play in a band so don't let the small wattage steer you away.

Good luck and happy amp building!

Here is a layout of my D'Lite filter cap board.
See the two 220K resistors?
Those bleed the voltage to ground as soon as the amp is shut off, draining the filter caps.
Not all amps have these though, so you got to watch it.

[lespaulplayer]

Thanks for the amp suggestions, but I am probably going to end up building a Marshall Jubilee 2550 clone for my first build. I really have no use for a Marshall 18w clone or that Fender. I already have a Fender Blues Deluxe, so that Fender kit wouldn't really do me any good. A bigger layout doesn't scare me. I know how to read the schematics, and I understand what all the parts of an amp do. I just wasn't quite sure on the proper way of discharging the caps, as I've seen about three different ways of doing it. I didn't know if there was a rhyme or reason for all the ways I saw. I just can't justify spending the money on an 18W clone when for a couple hundred more I can get the amp that I really want. I am confident that I can build this amp. Size doesn't scare me. I realize a smaller amp would be easier to trouble shoot, but I feel confident that I can do this. I really don't think that I'm biting off more than I can chew with that build. It's going to sound killer paired with my JCM 800 2203.

[M Fowler]

Draining the caps without using a resistor in series will fry the tiny wire in the filter caps. Such as the screw driver method.

Are you going to build a Ceriatone 2550 or go with a schematic?

Mark

[lespaulplayer]

Yeah, I'm gonna go with the Ceriatone kit.