Is it possible to convert an old stereo tube amp to a guitar tube amp?

Discussion in 'Amps and Cabs' started by TenThumbs, Jan 21, 2008.


  1. TenThumbs

    TenThumbs Member

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    Strange question I know, but I since the parts are all basically the same and there is input and output, I would think with some minor modifications, it might work?

    Stupid question or stupid person asking question; might be a little of both, who knows. Just throwing out a random thought to a group of folks who know a whole lot more than I.
     
  2. BSHARP

    BSHARP Member

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    Most older tube hifi amps are separated into power amp/preamp.
    If you have a power amp, it would be easy enough to add a guitar preamp and connect it to one or both channels of the power amp. Marshall and others have preamps specifically for guitars or you could use a modeler preamp.
     
  3. GVDub

    GVDub Member

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    A hi-fi amp, generally speaking, will have been designed to run much cleaner and be harder to push into the type of distortion guitarists are usually looking for. Generally it will be biased colder than a guitar amp with a comparable tube complement. Also the output transformer will be designed for full-range response rather than the band-limited response many OTs for guitar amps are. So, while you could get a preamp and plug it in, it's not going to sound much like a cool tube guitar amp.

    My advice would be, rather than chopping something up that might be fairly valuable to someone in its original state, to either use it for its intended purpose, or sell it to someone who wants it for that, and invest in something more suitable for guitar, like one of the many fine amp kits now available (if you want the hands-on building experience).
     
  4. Steve Dallas

    Steve Dallas Supporting Member

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    Sure it is!

    The Dr Z Ghia is based on a Hammond AO35 reverb amplifier. I have some old Moviolas that were supposedly used in movie theaters. They scream! There is a business near me that does this routinely and shows up at every Dallas area guitar show. They are called "Recycled Sound" IIRC.
     
  5. PRNDL

    PRNDL Member

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    It depends on the amp. I've done about six or seven such conversions, and each is different.

    The first one was an old Heathkit amp, which involved removing an RIAA tone circuit, modifying the James tone stack for guitar, and changing the first preamp tube gain.

    I recently converted a Precision PA amp, which involved new tubes (7868's are $25 each - ouch!) and a completely new circuit (based on the Ampeg Portaflex). I ended up covering the metal case in tweed and call it the Jazz Tank (because it's built like a tank).

    The last one was a Fanon Stereo HiFi (mono) amp, which I believe was built in the 50's. I ended up scrapping the amp because it was a point-to-point nightmare and the underlying tone was horrible. I put in a unique design using the 1-watt 6AK6, which sounds fantastic.

    I suppose the easiest was the Retro 6V6, which involved using the transformers and tube sockets from an old organ amp. Everything else was new. It has a nice high-gain circuit based on the Matchless Spitfire with an extra gain stage. I sold it last week to a guitarist from Austin.

    There are photos on my web page, if you're interested.
     
  6. bosstone

    bosstone Member

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    Old PS amps would get you a lot closer to where you want to go. Personally, I have had $3K+ amps but there are many really great sounding used amps for $500.00 or less that would be better choices. Of course you can do anything with enough money and time.
     

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