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Thread: Preamp for Wurlitzer 420

  1. #1

    Preamp for Wurlitzer 420

    I very recently acquired a Wurlitzer 420 tone cabinet with Spectrasound module and self-contained power amp. I'm trying to match this with a suitable preamp, knowing only of the Leslie Combo Preamp.

    I've been told the 420 amp has an 8-pin connector.

    The model of Leslie combo preamp I'm looking at has a 6 pin output.

    I've located some parts which can take a 6 pin connection into being an 8-pin connection, presumably with two of the pin contacts unused. If I fuse this into a lead will I have joy?

    Are there any other preamps which are better suited to the Wurlitzer 420? I can find a couple of stripped out Wurlitzer organs online but I am a complete novice to any sort of wiring, I have a helper in my dad but would prefer a stock unit which would work for this purpose.

    I have a Wurlitzer 200A, Hohner Pianet and Hohner B2A Bass I'd like to run through this amongst other things and would like to get up and running. Thank you.

  2. #2
    Senior Member torea's Avatar
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    Welcome to the forum!

    The 420 is a pretty cool cab. I've got one and am adapting it for a Hammond without doing any modifications to the amp. Yours should have a 6-pin connector, wired differently from the Leslie connections you'll usually find. Luckily, you can still use it with a Leslie (147 style) if you make a jumper and don't need switching. Switching in these doesn't control the motor like on a Leslie, rather it controls the speaker connections. The Spectratone has a solenoid on top that can be wired into the crossover to give you an interesting effect, I believe it was meant to emulate a Leslie without having a lower baffle. There are 3 relays inside the 420s amp, these control whether that solenoid is in effect, and which speakers get what. It's interesting, and a bit complicated

    I have a diagram for making the jumper and motor switching, just like a Leslie 147-style single-speed. I'm going to build a separate box for these things, and mount it somewhere in the cabinet.
    Keyboards: 1972 Fender Rhodes Stage 73, M-111, M-3, A-100, M2 Desk(!), B3!
    Spinny things: Wurlitzer Tone Cabs (500 and 420), PR-40, 31W, 31H, chopped 31H, 125 (empty cabinet), 30A!!!

    Looking to Sell: M-111 and M3. M3 is like new body, plays great aside from a few small things. M-111 is a little worn but plays great!

  3. #3

    Thank you, torea.

    I would really like to see that diagram if that's ok with you?

    What I expected is that the amp would route the inputs into this crossover and distribute them to the different speaker sections, just like with a PA system, except that I'd get the rotary effect from the spectratone unit and that all I'd need is to allign the pins.

    Could you explain briefly what the jumper is?

    I can understand the motor switching but I'm not sure how it is different from simply playing the signal through the cabinet. Is this extra routing going to be necessary to get a tone out at an appropriate level?

    I would think the amp section of the cabinet has already been set up to route the input to the speakers in some way. Will I have to do too much work to begin with?

  4. #4
    Senior Member torea's Avatar
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    Let me draw it up in a cleaner fashion, I'll try to post it later today.

    Your signal goes in through the 6-pin, goes through the amp, and comes out through an 8-pin socket (I believe). The crossover (located on the top shelf by the Spectratone) has an 8-pin cable that connects to that socket. The 4 speakers connect to the crossover. You should have one small front-facing speaker (maybe 3"?), one large front-facing speaker (12") and two opposite facing speakers in the Spectratone (4"?). Unless someone's been tinkering around in there, it should all be hooked up just fine.

    To get sound into that 6-pin, you need a jumper cable to make it compatible with your Leslie Combo Pre. DO NOT plug the Leslie output straight into the 6-pin. The pinouts are different and you will kill your amp. Basically, the jumper cable changes the pinout to make the 420 amp compatible with the Leslie. The Leslie female plugs into one side, and the 6-pin on the amp plugs into the other. It's fairly easy to make.

    The extra motor-switching modification that I mentioned doesn't do anything to the signal. It basically just creates an On/Off switch for the Spectratone motor. When stock, the 420 amp leaves the Spectratone motor spinning at all times. This is because their switching system isn't the same as the Leslie system, and doesn't require the motor to stop. I want to be able to stop the motor (and the rotary effect) whenever I please, so I'm making that modification. Definitely not necessary, but I think it'll add flexibility to the cabinet.


    Once you make the jumper, you can use the cabinet. You'll have full function, aside from the switching.
    Keyboards: 1972 Fender Rhodes Stage 73, M-111, M-3, A-100, M2 Desk(!), B3!
    Spinny things: Wurlitzer Tone Cabs (500 and 420), PR-40, 31W, 31H, chopped 31H, 125 (empty cabinet), 30A!!!

    Looking to Sell: M-111 and M3. M3 is like new body, plays great aside from a few small things. M-111 is a little worn but plays great!

  5. #5

    here's a picture with the 6 pin labeled(please excuse the sloppy writing did it with the mouse)when I got my 420 it came with a set of wurlitzer halfmoon switches,to power the 420 I clipped the ac wires running over to the 6 pin and took 2 lamp cords and spliced them together so it has 2 male ends and run it into where the motor for the spectratone goes,just use a power strip and plug them both in there,the half moon switch is labeled off/chorus/tremolo,off is just the 12" speaker,chorus is 12"+spectratone+4",tremolo is just the spectratone,the solenoid is a great effect,I am going to add a 2 speed motor to mine,I love micing the spectratone whilst in slow speed,these 420's are awesome speakers and I like them better than my leslie horn/drum cabinets,I wish I had about four of these wurly cab's,not to mention there pretty damn loud as wellPicture 003.jpg

  6. #6

    Is it possible to stop the rotary effect by jamming the spinning speaker or would that do damage? I'm half-joking with that question. The motor switching sounds like a very logical modification, I think I'll try the jumper cable first, just to get my feet wet.

    I'm with you so far and I'm looking forward to seeing your diagram, it'd be a great help.

  7. #7

    Thank you for this picture, peanut. So the halfmoon switch is an extra component which utilises the pins labelled 'switch?'

    I'm finding what you said a bit overwhelming. My overview so far is: 6 pin output- Jumper Cable - 6 pin input - 8 pin output into crossover. "Du bruit."

  8. #8
    Senior Member torea's Avatar
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    Quote Originally Posted by NWWlist View Post
    Is it possible to stop the rotary effect by jamming the spinning speaker or would that do damage? I'm half-joking with that question. The motor switching sounds like a very logical modification, I think I'll try the jumper cable first, just to get my feet wet.

    I'm with you so far and I'm looking forward to seeing your diagram, it'd be a great help.

    You just unplug the Spectratone. It plugs into the amp.




    Quote Originally Posted by NWWlist View Post
    Thank you for this picture, peanut. So the halfmoon switch is an extra component which utilises the pins labelled 'switch?'

    I'm finding what you said a bit overwhelming. My overview so far is: 6 pin output- Jumper Cable - 6 pin input - 8 pin output into crossover. "Du bruit."
    That's the basic overview, yes. Make sure to only plug the speakers into the 8-pin socket labeled Speakers! If you plug that into the 8-pin socket labeled "Second Cabinet" you WILL ruin your speakers by sending AC to your amps speaker system. It should be plugged into the proper spot, which is to the left of the input (I think. Don't have the cabinet in front of me).

    The halfmoon is included in my diagram. The pinouts are also included. In your basic jumper, you connect nothing to Leslie Pins 5 and 2, and nothing to Wurly Pins 5 and 6. In the switching modification, you would add in a 120VAC-coil relay and a pair of motor sockets. You'd probably need a .1uf/600V cap between the power line and the motor sockets too, it's not in my diagram. If you wanted, you could also add a switch on the box to connect 5 and 6.

    It's hard to see, but in the switch, the cap is .082uf, and the resistor between chorus and off is 56ohm. You don't need to ground pins 1. They're grounded in the amp and the combo pre.



    For the easiest route, just do the jumper, omitting anything connected to 2 and 5 on the Leslie side and 5 and 6 on the Wurly side. Hope that helps! Feel free to ask more questions, it looks a tad complicated but it's not that hard.
    Attached Images Attached Images
    Keyboards: 1972 Fender Rhodes Stage 73, M-111, M-3, A-100, M2 Desk(!), B3!
    Spinny things: Wurlitzer Tone Cabs (500 and 420), PR-40, 31W, 31H, chopped 31H, 125 (empty cabinet), 30A!!!

    Looking to Sell: M-111 and M3. M3 is like new body, plays great aside from a few small things. M-111 is a little worn but plays great!

  9. #9

    Thank you so much, sire!

    I'm planning to use these sockets. http://uk.rs-online.com/web/p/circul...PSF_396113|acc

    I'm unsure of what to use for the actual cable, peanut mentioned lamp cord which seems to be unshielded, is there any specific type of cable I should look for?

    Am I right in thinking I should have 4 wires for the first cable (6 pin to 6 pin?) Four thin wires which correspond with the correct pinout as shown in the diagram. So I'm just going to be threading cable into these sockets and soldering them in?

    Thank you. I think I'm almost there. My gear doesn't arrive for a few days but this has helped me a lot!

  10. #10
    Senior Member torea's Avatar
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    Why use those sockets? I'm guessing from the site you're in the UK? If so, I'm sure there's someone out there who has amphenol 6-pins. They look like these two - - -
    Plug - http://www.tonewheelgeneral.com/buil...tem_no=AMPH-6M
    Socket - http://www.tonewheelgeneral.com/buil...tem_no=AMPH-6F

    You need one of each to make this jumper. Your cable from the Leslie Combo Pre to the Jumper should look like this - http://www.tonewheelgeneral.com/buil...m_no=SPKR-CBL6


    As for cable, I used normal wire. I made a housing for my jumper, but you could just use 4 wires and heatshrink around em. You could use lamp cable if that's on hand, but I'm sure a hardware store near you has a small electrical department with stranded wire. 18 gauge should do the trick, for everything. Or you could do 18 for the audio and 16 for the power. You only need a few inches of each, just enough to connect one amphenol to the other. You also don't need shielded cable, it's such a short run you can just twist the pairs tightly by hand.
    Also, make sure it's rated highly. Seems obvious, but I overlooked it the first time I was doing this stuff.

    The amphenol socket has little holes you can thread the wire through, you can also crimp the rings around it. The plug is a bit more of a pain. You need a very hot iron and quite a bit of solder to do it right. You'll get the hang of it though.


    Glad to be helpful.
    Keyboards: 1972 Fender Rhodes Stage 73, M-111, M-3, A-100, M2 Desk(!), B3!
    Spinny things: Wurlitzer Tone Cabs (500 and 420), PR-40, 31W, 31H, chopped 31H, 125 (empty cabinet), 30A!!!

    Looking to Sell: M-111 and M3. M3 is like new body, plays great aside from a few small things. M-111 is a little worn but plays great!

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