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Thread: Leslie 22h Amplifier Questions

  1. #1
    Supporting Member
    Join Date
    Nov 2008
    los angeles

    Leslie 22h Amplifier Questions

    I'm working on a 22h amplifier; the solid state rectified version.
    The diodes in the main bridge rectifier are some that I don't recognize.They look a little like chocolate chips except they are yellow with a black base.
    There are also some ancient diodes in the motor brake circuit that look a lot like fat colorful disc caps.

    Should these be replaced as a matter of course and if so would IN4007s be an appropriate replacement?

    Thanks, Steven

  2. #2
    Noodle of Reality Steve Conner's Avatar
    Join Date
    May 2006
    Glasgow, Scotland
    1N4007s will do fine for the bridge rectifier.

    Can't say for the brake circuit as we don't know the voltage of it, but it looks like it ought to be less than 120V, so the 1N4007 should be fine there too.
    "Enzo, I see that you replied parasitic oscillations. Is that a hypothesis? Or is that your amazing metal band I should check out?"

  3. #3
    Senior Member
    Join Date
    Dec 2008
    You might want to check out a later 122 schematic--it's essentially the same amp except for the additional AC motor sockets.

    Leslie began adding an 8 Ohm wirewound resistor in series with one leg of the high voltage AC to the diode bridge to limit inrush current at turn-on--after some problems with the power transformers. As you note in your post, this was one of Leslie's first solid-state rectified amps. This 8 Ohm resistor became standard in all 122 amps from then till now. In fact, this resistor may have been added later in 22H production. I can't recall at the moment...

    Also, in 122 production, the four 0.005uF (later 0.0047uF) capacitors around the 6550s were changed from 1,000V to 1,600V, and, from then on, this was the standard rating for these components.
    Last edited by Rhodesplyr; 01-19-2012 at 03:28 AM.

  4. #4
    Supporting Member
    Join Date
    Nov 2008
    los angeles
    Thank you Steve and Rhodesplayr for your assistance on this project.It's now working well with the new diodes, e-caps and the 8 ohm 5W WW.

    Just a general question: How does one add a safety ground to a Hammond/Leslie system given the nature of the umbilical cord.Do you simply ground the Hammond and then add a chassis wire between the console and Leslie? Just curious..........

    Thanks again for the help...

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