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Vintage tube PA throwing down - Masco content

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  • Vintage tube PA throwing down - Masco content

    My converted '47 Masco MA25P phono top is a monster. It's got the sweetest jangly clean tone with a single pole loaded Strat. Plug in a Les Paul and it's a whole different animal.

    https://www.youtube.com/watch?v=wWRFxCSSVjI

    https://www.youtube.com/watch?v=w9D7MpHX80E

  • #2
    The vid is nice but Id be more interested in the conversion.

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    • #3
      I found it listed for $50 on Craigslist. A vintage radio guy near my office posted it and I caught it just at the right time.

      100% stock

      http://i706.photobucket.com/albums/w...psdd95c7f0.jpg

      http://i706.photobucket.com/albums/w...ps7e3ceab4.jpg

      Fully recapped.

      http://i706.photobucket.com/albums/w...pse0b23d23.jpg

      A number of values were changed to revoice channels 1 & 2. Channel 1 is set up darker than channel 2. It's big & deep, almost like a bass amp. Channel 2 is brighter with more gain. It's more Plexi like. The two are internally jumpered so you can adjust just the right gain & bottom thump. Channel 3, the phono channel. is connected to a jack out the back. I sometimes use that to plug in an iPOD. The last control is the global tone control which has a lot of range. The amp can be set clean and glassy which is especially nice with a single pole loaded Strat. It's very 50's Fender Tweed like. Plug in a Les Paul and turn it up and you get more Bassman inspired tone.

      It still has it's all lotal preamp section but I'm currently running RCA 6L6GT Black Plates in the power section.

      http://i706.photobucket.com/albums/w...ps16456529.jpg

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      • #4
        Is the HT CT still taken direct from PT to chassis, or is it now taken to the main filter cap negative directly?

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        • #5
          To be honest I don't know. I didn't do the conversion on this one. It was in such nice condition and I got it for such a good price I decided to send it to Skip Simmons to get it dialed in right. He is nationally known for his conversion work on Masco's and I wanted this one to be all that it could be. He did a great job on it.

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          • #6
            I do a fair bit of diy restoration of old PA amps for guitar use. There is a lot that can be done to electrically protect the amp nowadays - subtle changes that don't affect the character of the amp but do allow it a better chance to survive what can be a more onerous duty. Apart from adding over-voltage and over-current protections to the power and output transformers (as they are almost irreplaceable), other useful subtle changes include adding grid and screen stoppers to more gracefully cope with overdrive, and subtly changing some main grounding points to supress the worst hum causes. But those subtle changes take time and effort, and so would not normally be done by a professional service person who's main tasked job would typically be to 'recap the amp'.

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