Tube Amp Archive

I recently purchased this beautiful Hammond PR-40 Tone Cabinet. I pulled out the chassis' for future projects to be determined, and absolutely can not bring myself to do anything mean to this cabinet. It has two 12" speakers, and two 15" speakers, all 8 ohm. Guitar cabinet, right? I thought so.

Wiring it all up and putting a 1/4" jack on it would be too easy. I'm in search of tweakability, and thought of this idea, and quickly realized it would have severe impedance issues. It has a plate on one side that had two knobs. What I'm looking to do, is use one hole for the input jack, and one hole for the fader knob.

My idea that quickly brick-walled for this is attached. One extreme of the pot would be all 12" speakers 16ohm, the other extreme would be all 15" speakers 16ohm. (Or, something like 75% 25%) But then, at noon, all four speakers equally, but, 8 ohm.

There's got to be a way to do this, no? As for the pot value, that I'm also unsure of. The "necklace" reverb tank in there is coming out also. Anyone want it for the price of shipping? It's not worth my time to sell, and I'll never use it, as cool as it is.

Wow...all anico's...very cool. Since it usually doesnt hurt anything to operate into a higher imp. I would set my selector to 8 ohms (or 8 ohm tap) and go. You will get a little less power when you have the 16ohm loads, but again nothing will get hurt.

I tried to search for something with no luck. I think you want a pan control (pan left to right like with a movie camera) not a fader. I am thinking there is a pedal out there already built for this. Good luck.

RCGPNY1, I thought about just doing that, but really would like to see if something is out there, or a way to really do this correctly. Like you said, can't hurt, but I really want it to "do the thing".

Phil_s, thanks for checking into it. I'm calling it a "fader" as in when you're in your vehicle, you can use the fader on the stereo to hear more out of the front speakers than the back ones, and so on. The term Pan works for this also though.

Maybe, a 5 way rotary with compensating resistor network would get me more of a dependable or trustworthy method for this? I'd like to keep this cab at 16ohm if possible. Hmm...

Got to thinking some more. Maybe this is what you want?
http://www.musiciansfriend.com/amplifie ... -pan-pedal It offers left, right, and "center" whatever that is.

Phil_S wrote:Got to thinking some more. Maybe this is what you want?
http://www.musiciansfriend.com/amplifie ... -pan-pedal It offers left, right, and "center" whatever that is.

I think that pedal is designed for instrument level, not speaker level.

No pan pot available, wrong application. But you can build a switch box, one input jack (from amp), a DPDT footswitch, and two output jacks (to the two speaker groups).

I done something similar with a stereo l pad.
Get the most powerful one you can find , maybe 200w. It will probably be 100w per pot. And really only good for 50w.

Thanks very much for the thoughts everyone, very much appreciated! I'm gonna go like in this here schematical. The rheostat is coming from Hong Kong, I'll be sure to update everyone when I have it up and running in a couple weeks or less. Thanks again!

ps. Ya know that matt_h guy? He's pretty rad.

Woah, you guys gotta try this! This is really cool, I gotta say. I added a phase flip switch too, just 'cause I could. Neat neat neat this is neato.

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Confused by the desired results vs. the finished results? At 12 o'clock, in the middle of the rheostat sweep, the ohmage is 16 or thereabouts. And down in power by 25% (impedance mismatch) and then reduced from there another 50% by the rheostat. That's an overall reduction in wattage to the four speakers totaling 75%. You said you wanted an 8 ohm load, as if you had connected all four speakers in series/parallel.

What did I miss?

Hey rooster!

Maybe, you read my first post and interpreted the second to last paragraph as a desired result, which in fact was a paragraph explaining why my initial idea wouldn't work. (Maybe that's what you think you "Missed"?) I was looking for this cabinet to be 16ohms, through the whole travel of the knob. Or, rheostat.

At noon on a 30 ohm rheo, we have 15 ohms on either side. (Outer lugs) Both sides, have a pair of 8 ohm speakers wired in series, yielding 16 ohms on those lugs each. So, roughly 32 ohms per side. Since both two speaker strings are in parallel on the pot, we get 16 ohms.

When the rheostat is at zero, there's the 16 ohm pair of speakers on one side, and 30+16=46 ohm load on the other side. Again, parallel, gives 11.9 ohm. Close enough for R&R.

Like you did note and hasn't been touched on this entire thread, however, there's a loss in power. The cabinet isn't super loud, well, not as loud as you'd expect. But, since we're now aware, it can be expected.

I have to move yet again in about a month, so I'm selling lots of big stuff like this. Unfortunately, I had to let go of this kickass cabinet because I need the space, and the money is a bonus. Luckily, it went to a friend of mine. He's now enjoying it thoroughly with his keyboard setup.

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Hey guys,

I'm new to this site, and don't know much about electronics.
Cool Idea for the PR-40 cab. What did you do with the tube amp?
I have a very nice PR-20. (same speakers)
Are these good speakers?

I would like to add an input or two, and I guess I will also need a power cord wired up.
I believe the signal form the organ is amplified before entering the cab, (also, most likely a balanced signal), so I'll need to figure out the wattage before input, to solve the volume issue. Organs can get fairly laud, so the guitar should be able to get a pretty good sound as well if the same signal level is supplied.

Can I study the schematic and add to the existing five or six pin ? and wire the controls to a separate panel to maintain the organ connections? as long as I don't use the power cord when hooked to an organ?
The five pin form the organ supplied the power as well as the signal path.