[sdiy] My Hammond M111: to be restored and not used for parts

[anthony]

I finally broke down and bought this Hammond M111 at a local music store a 
couple of weeks ago that I'd planned to buy a long time ago - ever since the 
guy said he take $50 for it. He did explain that it had been the victim of 
some overhead flodding from an overflowing toilet from an apartment on the 
floor above and that the power transformer was burnt up. Undaunted, I 
figured I'd just take the main chassis and reverb amp (an AO44 - wished it 
was the AO35), reverb spring, two 12" speakers and one 8" speaker. I was 
amazed as I was removing these things that they showed no signs of really 
having beern affected by the water. And all of the motorized works was 
covered well, so I definitely wasn't surprised to see it still pristine (and 
well-oiled). But I still figured I'd just make a cool amp or two from the 
parts. I discovered that it was the reverb amp's power transformer that had 
burnt (if it's had a fuse it probably wouldn't have). My guess is a shorted 
filter cap. The good news is that I had a power transformer that was a 
perfect fit in every respect. I'd think it was a Hammond part, but there's 
no "AO-" part number stamped anywhere. Anyway, I figured the EZ81 was 
trashed too because a 1kOhm 1 watt resistor for the screen supply was burnt 
too (but I have a spare EZ81). I hope none of the ECL86's are trashed.

Anyway, as I started to fix this amp I decided that I wanted to actually fix 
whatever else needed fixing on the whole organ itself even if I had to 
completely disassemble both manuals - which considering what it's been 
through is probably where the problems will be. I regretted cutting the 
wires to the two chassis, but I tagged them all and reassembly should be 
simple.

But I don't plan to keep it stock. First, I'm removing the negative feedback 
on the reverb amp and the main amp too.

Then I want a momentary kill switch for the synchronous motor, external 
inputs for the scanner vibrato and the main amp.

I like the way Hammond drives reverb tanks: straight from the output 
transformer on the main amp with an attentuator made from a bridge of two 
resistors and two light bulbs. This puts the vibrato before the reverb, 
unlike most guitar amps with vibrato or tremolo and reverb. Ampeg's Echo 
Twin amps are the only ones I can think of that drive a reverb tank this way 
and then use a complete separate power amp - and they used either two 2x6V6 
or two 2x7591 amps - one amp being solely for reverb or an auxilliary input. 
Imagine a whole 2x7591 push-pull amp dedicated just for the reverb. I 
haven't read too much about them, but these must be surf guitar dreams! I 
once had an Ampeg VT40 which was rad iin its own way... But I digress...

So even though this is a synth-DIY list I'm counting the mods to my Hammond 
as a synth-DIY. I think Hammond organ chat has its place in synth-DIY. It'd 
still be nice if there were a mailing list (not a Usenet group or a 
web-forum) for Hammond organ stuff.

Cheers,
Anthony