converting Hammond reverb to guitar

[shovel]

I have an old Hammond organ reverb I want to use as a stand alone reverb unit and need to know where to start.Can it be done with what I have here?It uses 2 ECL86s and 1 EZ81.Thanks for ane help.

[Sweetfinger]

I had that same chassis, but with 2 EL84's. I ended up using the OP transformer in a rebuilt Harmony amp that had a tweed pro power section and a blackface pre-amp. sounded awesome! That should make a great little 12 to 20 watt amp, but you'll have to add a pre-amp tube and socket, or ditch the recto tube. Dig the little light bulbs used for current limiters.

[Arthur B.]

I have an old Hammond organ reverb I want to use as a stand alone reverb unit and need to know where to start.Can it be done with what I have here?It uses 2 ECL86s and 1 EZ81.Thanks for ane help.

Assuming that you've gone over the amp and checked that it's operatiing correctly, add a reverb tank to the output since I don't see one.You may have to rebias it into Class A to reduce power and improve linearity.

[shovel]

Assuming that you've gone over the amp and checked that it's operatiing correctly, add a reverb tank to the output since I don't see one.You may have to rebias it into Class A to reduce power and improve linearity.

I have the origonal tank and the amp worked when I took it out of the organ.I just need to know where to start as far as an input jack and a way to adjust the amount of reverb going to my Bassman Ten.

[john82]

hey what a great idea, i hope you can do it.
sorry i can't help i don't know much about electronics but please update if it works, i'd like to know... I also have an organ with a built-in reverb box, maybe i can make into a stand alone too.

_______
Johnny
http://www.guitars101.com

[Steve Conner]

AFAIK, that little amp drives the speakers inside the bottom of the Hammond organ itself, and the reverb tank was also driven off its output. But I think the exact wiring depends on the Hammond model.

The amp is total overkill for driving a reverb tank, way more power than you need, and would probably be unhappy without its speakers.

I know a guy who has a Hammond, and I know he disabled the speakers inside the organ itself because he plays through a Leslie, but I'm not sure what he did with his reverb tank.

[smothaudio]

Funny to stumble on this thread, I happen to be doing the same thing! Here?s what I did:

Basically I separated the verb recovery amp (the first stage with the transistor) from the rest of the circuit. I feed my signal into the tube part and into the verb tank from the output transformer, from there I took the output of the tank and fed that into the transistor recovery circuit and then to my amp.

I know the output of the amp is meant to drive a speaker, so I used a 20 watt 8 ohm adjustable ceramic wire wound resistor from the output to ground to take the weight, then I fed the adjustable tap from the resistor into the reverb tank so as not to over load it. I'm not sure how much signal the tank can take, so I just adjusted it up until I couldn't hear a difference and then backed it off a bit. I'm getting no clipping and it sounds clean enough. I put a 1M resistor to ground on the grid of the first preamp tube and a 1M pot from the grid to ground on the second for a drive control, plenty of unused gain, but I don't mind... I also got rid of the current limiting lights, and the feedback wire.

It's a crude dirty Frankenstein job, but it works-though has a few minor bugs to iron out. I have plans to replace the rectifier tube with diodes, then use the empty socket for a 12ax7 stage to replace the transistor circuit and enable a wet/dry mix and a tone control (like the fender 6G15). I currently use a 2 channel fender bassman amp. I split my guitar signal and feed one into the modified reverb unit with its output going into channel one and take the dry branch into channel two. Then I can make a nice wet dry mix with independent tone controls. It's interesting but still requires some more tweaking. I think once I put the tube in, get all my levels right and make the wet dry control, I?ll be a lot happier.

Best of luck!

[imo]

these are great guts for an AC15 style amp. I made one out of a similar part, used the El84's, used the 12AX7, subbed in a Ef86, and used an EZ81 rectifier.
Thing sounds awesome, and took only a few hours to put together
Ian

[olddawg]

The reverb unit seems to be a separate chassis from the main amplifier in these units. Everyone is suggesting to convert the reverb unit to a stand alone amp. It was not used as such in the original organ. It was used with another amp chassis and a small internal speaker. There should be a way to convert the reverb unit to instrument level signal and add some controls (intensity, dwell, etc). Here is something similar on eBay with all of the parts: http://search.ebay.com/_W0QQsassZshortsets

Also with the repro Fender stand alone reverb units being inferior and rather pricey and with the originals being virtually gold plated, it would be a great project to pick up one of these Hammons for $50 or so and convert it to an approximation of the Fender. I have not compared the schematics. I was going to build a Fender Reverb from scratch once and found it would be cheaper and easier to buy a new repro and convert it to original specs. It seems that if you get a usable chassis, the right transformers, and a good tank with these Hammons it might be a much cheaper and not too dificult way to do it. Then again, if it was tht easy, everyone would be doing it.

[Marc]

I'll second Ians' post. I've used these amps several times for very nice AC-15 / Spitfire clones.

Marc