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Thread: Hammond PR-40 Questions

  1. #1

    Hammond PR-40 Questions

    Hello Hammond Fans

    I'm new and I mis-spelled my Handle which is suppose to be Platefire as I'm know on
    tube amp forums I hang out on. This is a question for those familiar with the electronics
    on Hammond Organs. I recently picked up a Hammond PR-40 tone cab at a flea Market.
    I've been studying the cab and its history with info I've got off the net. I've got several
    schematics on it so I'm in good shape on that. I haven't got any hammond organ that has
    the six pin connection cord to my tone cab so I'm making plans to rig a connection that
    I can test the cab. In my salvaged parts from old amps I have found a female 6 pin socket
    to fit the 6 pin male socket on back of the power supply chassie of my PR40. I've also found an old chassie with a fuse holder in it. My plans are to wire the chassie up with a three conducter power cord to the fuse and install a SPST power switch and run power to my 6 pin female to pin #3 & #4 where my cab recieves AC power.

    I've looked at all the schematics on hammond amps and preamps and I can't find a
    reference to the AC power coming from the console to this cab. My questions is--------
    WHAT SIZE FUSE DO I NEED TO USE IN MY CHASSIS TO PROTECT THIS PR-40 AMP??
    I can't find any reference to fuses on the schematics I've found!!!

    Also I'm planning on my connection chassis that I am building to install two 1/4" jacks to
    receive stereo input from my Guitar preamp/processor or from my Yamaha Keyboard
    that will be routed to pins #1(G2) and #4 (G10) which is the preamped signal from the console. I'm kinda thinking out loud what I think will work. I'm really wanting to give this tone cab a test to see if it's operational and see what it sounds like with guitar and keyboard. So to sum it all up this will be a seperate little chassis with my preamp inputs and AC power to it with a long enough cord to extend from in front of the cab around back to make the connection on the power supply chassis. Please!! If you old Hammond Heads would take a look at this and see if you think it would work and maybe give me a fuse size and any other comments, I would appreciate it. Thanks, Platefire

  2. #2

    Re: Hammond PR-40 Questions

    If I remember correctly the PR-40 has 40 watt amp so it's probably not going to draw more than 100 watts. I'd guess a 1 amp slo-blo fuse to start with.

  3. #3

    Re: Hammond PR-40 Questions

    if you find you don't like the amp for guitar,i'm looking to buy one for my hammond organ,and would maybe buy it depending on how far away from 10312 zip.AL---the amp is made for a balanced G-G input so if you don't feed it that it's going to electrify you pickups,be carefull.

  4. #4

    Re: Hammond PR-40 Questions

    You will not find any older Hammond organs or cabinets with fuses. Mr. Hammond was paranoid about sending out factory service techs long distances to replace a fuse. I thought that kind of thinking was askew but that is how it was as I learned from inside information. I have replaced power transformers in customers tone cabinets because of the absence of a fuse. I would think a 3 amp slo-blo fuse would work.

    The PR-40 will sound "tubby" to you if you use it as you are planning to do. I would suggest enhancing the PRs speaker compliment by adding a good horn type tweeter.

    As you are fond of "Glass Audio" my suggestion would be for you to obtain an old pre-amp from a B or A model organ with the tube compliment of 56 and 57 tubes. There should be plenty of them around as the latest generation of "Hammond Heads" replace most of them with Trek II preamps. (I might even have one in my collection of parts if I ever get to sorting them out.) With this pre-amp you should also obtain a six conductor organ cable and wire everything up as it would be in the organ application. Then you can simply put the output of a simple mixer to the input of the pre-amplifier and away you go.

    EDIROL (Roland) makes great studio speakers that I would think would do your Yamaha Keyboard much more justice than the PR-40 cabinet would. Your PR-40 will sound best standing against a wall but try to put a tweeter horn on it.

    Gary K.

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