[HAM] HR-40 spring reverb unit advice?

Mon Jul 2 14:00:28 CDT 2007

Robert,

  I'll try a little for you.
  I recall using the HP450a when I was on submarines during the Cold War. It was a major piece of our test equipment on board but I'll be darned if I recall much about it. I have my tech manuals around here somewhere from when I took a Navy Auxilliary Equipment course that partially covered the HP 450a. If I can find it I'll try to give you more info if it's in there.

  As for your slider, that is a manual "switch" if you will. It is a locking mechanism to lock the springs from too much movement during transit or moving the tone cabinet around. It is not an automatic thing that controlls the sound or springs. It has a little nitch that you move the lever a certain way to allow it to push in or pull straight out to lock or unlock.

  Hammond Oil is what was used in the reverb tubes and I don't believe it came in any viscosity except one and I don't know what that weight is. Hammond Oil is easily available on eBay or other distributors. For your purpose though, I think I'd simply experiment with a light oil like sewing machine oil which is probably cheaper than buying enough Hammond Oil.

  Good luck.

  Ed

Robert H <rch427 at yahoo.com> wrote:
  Hello -- my first post here, so I'll throw in a brief introduction. I'm not an organist, and I don't own a Hammond tonewheel organ (auspicious start, eh?). If it counts, I have a Solovox that I'm restoring, but I'll have to leave the questions relating to that for another time. I'm primarily an experimenter, and I'm putting together a sort of giant modular synthesizer made up of about 20 pieces of old tube-powered bench gear -- sine/square generators, random noise generators, oscillators, etc. One element of this device (which takes up 5 shelves of a custom-made 4 by 5-foot rack) is a Hammond HR-40 spring reverb unit -- the early column-shaped type with the oil-filled tubes. I picked it up on eBay and need to convince it to work with the rest of the system, hence these questions:

1. I've been able to find the schematic on-line for the HR-40 tone cabinet, but they don't seem to address the detached spring reverb unit. I understand that the HR-40 puts out 40 watts peak, but I don't know how much power is actually diverted to the reverb unit, nor what power level below 40 watts could still drive the unit. The amp I'm using is a Hewlett-Packard 450A laboratory amp, and damned if I can find the power output specs for it; just that it produces 40dB of gain. I have a few other (more powerful) tube amps I could substitute, if necessary, but I'd rather stick with the HP, since it's actual laboratory gear. I know -- weird project.

2. There's a sliding lock for the springs which moves over to allow them to vibrate, but I have yet to be able to figure out what actuates the slide. Some sort of servo? If so, I presume it's a lower-voltage DC power? Any kind of cheap/dirty way to actuate this, short of just removing the connection from the control arm entirely and sliding it manually?

3. I've read criticisms that the HR-40 tended to produce reverb that sounded like it was produced inside a rain barrel, with negligible effect on the higher frequencies. Anyone know of any way to modify it to produce a better effect? Using a higher viscosity oil in the tubes? 

That's enough for now. Any advice would be appreciated, other than "get rid of it and buy a proper B". 

Thanks -- 

Robert

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