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Organ tube amp wattage?

Discussion in 'Amps and Cabs [BG]' started by jondog, Nov 28, 2002.


  1. jondog

    jondog

    Mar 14, 2002
    NYC metro area
    Hi,

    Last summer my wife bought me a Wurlitzer tone cabinet to play around with. It's basically a Leslie clone but only the treble horns spin - there is no baffle for the bass speaker. I spent several weekends working on it, and was very proud of myself when I managed to bypass the 6 pin input to give it normal wall power and a regular 1/4" jack.

    It works with guitar and bass now, but my problem is volume. I have tried multiple preamps, but my tone always ends up distorting before it gets very loud. The distortion is pretty cool, but I would like to be able to choose loud and clean also. This amp is rated at 185 (tube) watts, so I was expecting a lot of volume.

    Does anyone have ideas on what I should try next? Do you know of any good boards that organ tech people frequent?

    Thanks!
     
  2. I've never seen one of those tone cabinets with that much power. It's usually about 40 Watts max.

    What kind and how many power tubes does it have? I can tell you the real output power from that. EL84's, 6550's, 6V6's? 2, 4, 6, 8?

    That 185 Watts you mention is how much power it sucks from the wall, not how much it puts out.

    Chris
     
  3. jondog

    jondog

    Mar 14, 2002
    NYC metro area
    It's got a pair of 7027As as power tubes. It says 185 watts on the chassis and 215 on the back plaque. I know that's a lot, but this doesn't go nearly as loud as my 50 watt Sunn.
     
  4. Pair of 7027A's will give no more than 60 Watts output, and more than likely only 50 Watts. That's what my Ampeg B25B uses, and it puts out 55 Watts. You'd need (8) 7027A's to get over 185Watts output.

    Those 2 nameplates that you refer to are showing the power the unit(s) will use when plugged into the wall, not what the audio output is.

    You may need to tweak the circuit to get it as loud as your Sunn, which was designed for Bass signals. I'd recommend modifying the circuit to make it more like the B25B.

    Let me know if you need help. I design and repair tube amps for my hobby, and I'm an electrical engineer.

    Chris
     
  5. jondog

    jondog

    Mar 14, 2002
    NYC metro area
    Thanks for your help. Do you know any simple tweaks I should try? I'm not sure my skills are up to real "modifications." It took me several days to get around the 6 pin input. :)
     
  6. I don't know the 420 schematic, and couldn't find it on the web, so I don't know specifically what to do. The good thing is that tube amps are all pretty much the same. Give me a listing of each tube on the amp so I'll know what I've got to work with.

    I'd say do what is necessary to change the circuit into an Ampeg B25B or something similar. You'll need (1) 12AX7 and (1) 12AT7 or 12AU7 to go along with the pair of 7027A's and you'll be good to go. You can leave out the tone controls and just have a volume control and it will sound really great. I run mine basically flat anyway. It won't be tons louder than it is now, but it will sound better since it will be voiced for bass guitar.

    Give me the tube lineup and we'll go from there.

    Chris
     
  7. jondog

    jondog

    Mar 14, 2002
    NYC metro area
    The other tubes are 12AU7A, 7199, and 5U4GB. It has volume, treble, and bass knobs. The tone now is pretty good, just quiet.

    Here's a pic of the back panel. Unfortunately, my digital camera died so I can't give you pix of the chassis itself.
     
  8. OK. The 7199 is a good tube, but expensive for USA made ones. 12AU7 is common as hell. 7027A are great tubes, but expensive. They last forever, so yours are probably fine.

    Without seeing the original schematic, I can't really tell you how to improve upon it, other than just ripping out the stuff that's already in there and rebuilding from scratch. You may not be into that kind of thing, and it's a bunch of work.

    If you haven't already done this, replace the power supply filter capacitors. They may be almost dead. That will probably give you a little bit of improved performance, and may give you a lot of improvement.

    3rd option, put it on eBay, recoup your money and use it to buy something normal that's easier to work on and such.

    Not a whole lot of help, but you may not want to put in about $150 worth of parts and 20 hours worth of work to get something that's still not as good as your Sunn. If you want to learn a lot, use the amp as a test bed to really learn this stuff, and go from there.

    Chris
     
  9. jondog

    jondog

    Mar 14, 2002
    NYC metro area
    If you haven't already done this, replace the power supply filter capacitors. They may be almost dead. That will probably give you a little bit of improved performance, and may give you a lot of improvement.
    --------------------
    This seems doable. What do they look like, and where do I find them.?
     
  10. Chasarms

    Chasarms Casual Observer

    May 24, 2001
    Bettendorf, IA USA
    Remember that the amp was designed for use with the keyboard which is electric. I don't know about them, but I would imagine there was some kind of preamp that was involved in the input signal.

    If you are using a passive bass, you may have much less output voltage going into the amp than the amp is designed to function with.

    Just a guess, you'd need to check it out.

    Chas
     
  11. jondog

    jondog

    Mar 14, 2002
    NYC metro area
    Yeah thanks. I've tried active basses and different preamps, but I always get thick distortion before any significant volume.