Convert Organ Amp to Guitar Amp

[jeepney]

I have a mid-60's Estey console organ which I am considering removing the amp (and perhaps speaker) from. I would like to convert it to use as a guitar amp. Before I commit to dismembering it, how feasable is this? And, are there any good books anyone could recommend?

My electronics experience consists of wiring my own guitars (pickups, pots, switches, etc.) and that's about it.

Thanks for any advice.

[sportster4eva]

Here's a good article to read.

http://www.geofex.com/Article_Folders/old2new.htm

Although meant for PA amp conversion, it can be useful when converting an old organ chassis as well.

If you are new to vacuum tube electronics be VERY careful, there are lethal voltages in there. Make sure you take every precaution and word of advice from the various threads on this board about safety. Search around and get familiar before jumping in to a project like this.

Good Luck and have fun!
Paul

[Rob Mercure]

Jeepney,

On the positive side your organ amp probably has an output tranny that doesn't roll off until you get around 20-40 Hz which means that you can get "some" (I dunno, 20-50% guess) more power out of it if you only use it for guitar which really doesn't go below 80 Hz or so.

On the negative side the chassis's "aspect ratio" (size, porportion, dimensions) are probably poor for a guitar amp, it's likely heavier that an similar sized guitar amp chassis, you may have far more tube sockets than you'll ever need (depends on the model - maybe a positive) and any tone controls are centered at a point in the audio spectrum that may be unusable. And the speakers may be a tad too "flabby" for good electric guitar work - from my experience it's about "50/50" - some are crisp and punchy (if a bit bass heavy) while others are kinda "sweet" and perhaps appropriate for an acoustic instrument but flab out under a distorted run. Oh, and all of the plugs are probably something you've not got.

Even more negative(/"positive") is that the amp/organ may be worth much more as replacement parts to someone restoring an organ than as a "guitar amp kit." Might I suggest that you do a bit of web searching, perhaps a flea-bay listing, and see what the beast is worth? It might fetch sufficient monies to either buy a kit or a "beater" old HiFi amp to convert, or even a good factory guitar amp that you may like.

But there were scads of organs made with amplifiers ranging from 2-3 channels with Leslies and great high quality speakers to plastic cheapies with the audio amplifier modeled on a clock radio <grin>. If you get a chance could you provide us with your tube line up for at least the power amp? Such as what output tubes you've got, which rectifier (if tube) and maybe those tubes within about 12" of the outputs (you've probably got a zillion 12AU7s or such but we're more interested in your power amp)? That way we might be able to offer some suggestons about the feasibility as a project.

Rob

[sportster4eva]

+1 on everything Rob said.
Organ amplifiers are getting decent money on auction, about the same or a little less than old P.A. heads. Guys like us scoop them up to use for parts. They often have good OT's but the power tranny is way big for use in a combo. You got about 50 filaments to light up in an organ. If you have a mind to, you could just gut the chassis, and reconstruct it in a nice smaller Hammond box, but there's that monster power tranny again. There's a lot of goodies in those old organs, but it's up to you whether you keep it all and use it for parts, or sell it off to fund an "easier" project. If you intend on making more amps, you'll have plenty of parts, but if you just want to make one you're probably better off looking for a PA head or an integrated to convert.

[rh2music]

Book recommendations

I have a few Baldwin organ amps myself, and as far as converting for guitar, yes it could be done. But the power tranny as mentioned earlier is a monster.. You wouldn't want to carry that in a combo. Maybe start out by converting it into a head unit, is it a 6L6 amp? If so, you might be able to convert into a Fender Bassman. A pretty simple circut considering it was one of the first guitar amps. Check your local library, I discovered my library has a lot of old music and audio books and a few fender vintage books or the History of Fender, which has some amp schematics. Otherwise check out 2 books by author Morgan Jones, Building Valve Amplifiers, and Valve Amplifiers. they are available at www.newnespress.com or online.. The first book mainly deals with the construction of amps, how to do metalworking, etc and some basic building blocks. For free online stuff check out www.pmillet.com --free tube audio and technical books online. hope this helps.

[tantalune125@aol.com]

Organ amp question, too...baldwin (4) EL84's

Greetings!
I have attached some pix of another brand of organ amp. Slight pre amp dilemma...
- Can you recommend a company, or individual, who has experience, and who can do a rack pre with line level output?
This Baldwin amp seems small enough and not too heavy to lug around. I bought it for amplified blues guitar, or harmonica. Both high impedance.
I fancy a 59 Bassman output, with the EL84's incredibly smooth buttery bottom, midrange, highs, and over all tone and crunch.

- What will it take to get the project moving?
.....As I am an amateur at this. I am willing to ship anywhere if it can be done promptly and professionally.

- Any suggestions as to type of outboard pre amp?

- And is there a way to find out how hot a signal it is expecting to see?

thanks....here's some pix of the trannies and the i.d. numbers...hope it helps..

[luthierwnc]

I've done a bunch of conversions. Ideally, you pick the amp to match the need. If you are starting with the amp, you have to assess the limitations in advance. The size limitations mentioned above are one of the biggies. Organs have a lot more controls but they aren't on the chassis. Allowing room for pots, switches, inputs, etc. determines the build. Since each one of these is a prototype, you have to spend a lot of time in advance working up the layout diagram. Keep the grid wires away from the power and heater wires, be prepared to shield even short runs. Allow for capacitance in those wires and adjust caps accordingly.

Compared to the orderly wiring we see (especially nowadays) in high-end guitar amps, most of these old point-to-point jobs look like someone just dumped the components in. Not so. The runs are generally as short as possible, grid stoppers are right on the tube sockets. You know that a lot of their prototypes were stripped and redone until they worked out the gremlins. You won't get as many chances.

Another thing to consider is that a lot of these amps don't have much wire in the HV section of the power transformer. Most of it is for the oddball filaments. I have an "M" hammond PT that has the same footprint as a Twin Reverb trannie. 325-0-325 no load but it can only manage 390 VDC with a pair of 5881's using fixed bias. Don't try to drive too many amps just because the iron looks beefy.

The last thing I'll say here is figure out your faceplates before you drill the holes. If you have those custom made, glue a working template to align the parts. A lot of times, these donor chassis' aren't as deep as a guitar amp so you can't put the components exactly halfway from top to bottom. The upper of the two amps shown is a Hammond chassis and I had to pinch things in a bit compared to the custom-bent chassis below.

Have fun, Skip