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vince8 7th October 2003 10:37 PM

Hammond guitar amp-
Am curious if anyone has taken ,(specifically) a tube amp with 7951 output tubes and (apparently) no tone controls, and turned it into a decent guitar amp. I've limited experience..but have built a few kits and modified a few pieces of equipment (with help) Thanks-

planet10 8th October 2003 05:52 AM

Re: Hammond guitar amp-

Originally posted by vince8
Am curious if anyone has taken ,(specifically) a tube amp with 7951 output tubes and (apparently) no tone controls, and turned it into a decent guitar amp.
Not yet, but i have raw material in the lab... quite a few others in the queue ahead of it.


jkratz 17th March 2004 09:42 PM

Organ to Guitar conversion...
Hey! Converting a church organ: does it become a mosque organ, or -- sorry. For my first post I should be less flippant. I've got tons of useful raw paterials, knobs, speakers, leslie bits, etc. from old organs, a there's a piano/organ place nearby. Stands to reason the Hammond's a good source for the whole amp section, neverminding the difficulty replacing tubes, perhaps, but the tone source is just filtered magnetic pickups looking at toothed rotating "tone wheels". I have the unpopular version of one of these (L-101) gathering dust in the barn. (Anyone in SE Pennsylvania have a pickup truck and a reasonable offer?)

Someone will have to point out that the spring reverb comes to us out of electric organ technology, so I'll do that. Here's a trivia question: Who's label says something to the effect of: "Made under controlled atmospheric conditions by beautiful girls in Milwaukee,WI"?

I pose the question this way 'cause I can't remember the name here at work. It's a silver label on the "Folded Line Reverb", a spin-off of Accu-tronics, the original Hammond spring...what was the topic...? Oh yeah.

Let us know how you do.

Mark_S 20th March 2004 06:51 PM

2 Attachment(s)
you may want to take a look at the Vintage Silvertone Guitars and Amps forum. A few of the members there have been doing amp conversions (pa amps, tube hi-fi, and tube organ amps). One of the most recent is a Hammond PR-40 Tone Cabinet ( an add on preamp to drive a stock cabinet)

Vintage Silvertone Guitar and Amp Forum


here's a picture of the label on one of those reverb tanks that you were talking about.

jkratz 29th March 2004 06:17 PM

Folded Line reverb
Thanks --
I have two of these in the garage; I thought it was a hoot the first time I read that. Only a technician would even see that. I did make a passive Leslie cabinet by mounting the frame, motor, and spinning styrofoam cone inside a plywood box. It has a simple hi-low speed switch, the motor switch to get it spinning, and only it's own speaker wired directly to an input jack. The sides of the box are ported to let the sound out, you mike it from there or just let it warble near your audience for effect. You need a speaker-out signal from your amp to run it; this keeps the design simple. If anyone wants a step-by-step I could talk you through it with pics and all. The whole frame is easily removed from old organs with hand tools.

I'm a recovering stomp-box schematic addict with a cabinet full of Bazz Fuss and Electra IIbe's and the like. Hi. My name is Jonathan.


Mark_S 29th March 2004 07:45 PM

I salvaged that reverb tank out of an old Traynor MX6800 powered PA mixer. That was about all that I could save out of it though. It was "stored" in a barn for about 15 years before I got it.

I haven't done much with organs myself though. Do Hammond organs use a seperate chassis for the preamp, volume, and tone controls? Or do they just come off of the tone ring pickups to a passive volume and tone stack?

Does that amp chassis have any smaller preamp tubes?
(12a_7 or somthing like that)

jkratz 2nd September 2004 08:14 PM

Try this link to a schematic of the organ. The aluminum boxes the circuits are in are stamped as shown in the drawing. The rat's nest of thin wires towards the top are daunting, but I may bite the bullet and start sacrificing this thing for the purpose shown, if I can back-track from the speakers and decipher where "sound goes in", and will let y'all know how it goes. Plug the guitar into one magnetic pickup line, tape off the rest, and use the drawbars for effect? Split the signal and run it via several drawbars? No takers? No...?

That's where I got the schem. Impact Thrift is where I got the organ. I'm in Horsham, PA, if anyone wants to stop the senseless slaughter of vintage tube audio equipment. This gentleman...

... has nearly got me rearranging the house and going, no! Don't kill it! Find it a corner to quietly sit's old, it's special, it's...

It's getting eaten by mice, and weighs 500 pounds plus an inch of dust, is what it is.

Brett 8th September 2004 11:21 AM

Not wanting to threadjack, but I've just got a couple of Jensen F12 field coil speakers from '51 that are apparently used in Hammonds. Any idea on the specs or how to energise the coils correctly? Or some idea where I might find out?

kyletgood 10th October 2005 06:22 AM

needing some help with conversions
hey i'm new here.
i have heard many talk about the possibility of converting hammond organs into guitar amp. i just salvaged one not sure of the details to it. it has a built in leslie, 2 12's and a spring tank. i dont know if hammond have built in tube amps or what not. so if anyone could break down whats commonly inside of the hammond organs, and how you would go about building a guitar amp from one it would be appreciated. plans or schematics.

i would like to be able to get this going and add a gain channel and foot switches for the trem speed and the reverb, also a switch on/off for the gain channel.

again any help would be greatly appreciated.\


oh and does anyone know what kind of speakers were used in many hammond organs? i have heard jensens. but there are no obvoius markings on the ones that i have.

Mark_S 10th October 2005 04:42 PM

I might be able to help identify the speakers.

Is there a 6 digit number stamped on the speaker, like 220607 for example?

the first three digits stand for the manufacturer and the last 3 are the date code.

the ones in my guitar amp for example have 220607
220 = jensen , 6 = last digit of the year (1966 in this case), 07= the seventh week of the year

Weber speakers has a website that lists manufacturer and date codes here.

common ones are

220= Jensen
328= Utah
285= Rola

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