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Thread: Recommended silicon rhodes peterson design output transistors?

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    Member parentheticalfact's Avatar
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    Recommended silicon rhodes peterson design output transistors?

    Anyone have a recommended silicon replacement output transistor for the rhodes 80w peterson amp? Perhaps even some recommended replacement resistor values for proper bias. Got two dead ones in my rhodes and thought I'd go this route as opposed to installing completely different power amps.
    Any help would be greatly appreciated!

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    Old Timer tedmich's Avatar
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    some numbers as to what the heck transistor this is would be helpful, as my rhodes 80w peterson amp schematic tattoo won't be finished for another week, and is difficult to see in the mirror...

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    Old Timer tedmich's Avatar
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    already discussed here I believe:
    http://music-electronics-forum.com/t22175/

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    Quote Originally Posted by tedmich View Post
    some numbers as to what the heck transistor this is would be helpful, as my rhodes 80w peterson amp schematic tattoo won't be finished for another week, and is difficult to see in the mirror...
    The peterson rhodes amp uses the long discontinued delco 120725 germanium transistors. There are mods semi common (I.e. Vintage vibes rebuild kit) mods that replace these with silicon for added stability and better parts availability but require different biasing of course. I'll post the schematic later today. I know it's a common enough practice to convert this amp, but haven't found much Info for a recommended modern (available and affordable) transistor to sub in with some resistor changes.

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    Member parentheticalfact's Avatar
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    Quote Originally Posted by parentheticalfact View Post
    The peterson rhodes amp uses the long discontinued delco 120725 germanium transistors. There are mods semi common (I.e. Vintage vibes rebuild kit) mods that replace these with silicon for added stability and better parts availability but require different biasing of course. I'll post the schematic later today. I know it's a common enough practice to convert this amp, but haven't found much Info for a recommended modern (available and affordable) transistor to sub in with some resistor changes.

    Schematic here. http://www.fenderrhodes.com/org/ch11/fig11-9.jpg
    I'm really much more of a guitar pickup and tube amp person so my knowledge of common output transistors is very limited.

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    Old Timer tedmich's Avatar
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    Yah Steve goes into some detail on these (usually DTG110B) which usually require matched silicon replacements, he also recommends checking the driver transformer and replacing all the associated resistors
    Steve's Corner - Common Amp Failures

    see also RGs white paper on transistor subs for similar organs
    http://www.geofex.com/Article_Folder...placements.pdf

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    Member parentheticalfact's Avatar
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    Quote Originally Posted by tedmich View Post
    Yah Steve goes into some detail on these (usually DTG110B) which usually require matched silicon replacements, he also recommends checking the driver transformer and replacing all the associated resistors
    Steve's Corner - Common Amp Failures

    see also RGs white paper on transistor subs for similar organs
    http://www.geofex.com/Article_Folder...placements.pdf
    Wonderful info here, thanks so much! I had found some of these links before but somehow haven't been able to find them lately. Much appreciated!

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    Lifetime Member Enzo's Avatar
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    Any silicon you put in there will make similar changes, and as long as they fit and meet the minimal specs, they will work.

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