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Help needed sourcing power transistors

Discussion in 'AV Pre-Amp/Processors & Power Amps' started by fraggle, Aug 25, 2005.

  1. fraggle

    fraggle
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    Hi,

    I've diagnosed my Primare 30.5 and found one of its channels has blown all its output transistors. (thank god they saw fit to put seperate fuses feeding each of its 5 mains transformers!)

    Anyway, I'm trying to find the following :-

    Toshiba 2SC5200
    Toshiba 2SA1943

    two of each, must be matched across all four. (I know you can get matched pairs, but unsure if you can get matched quads?)

    Interestingly enough the same channel has been previously repaired, the first driver stages have been replaced at some point - maybe causing damage to the outputs causing them to fail now?

    If anyone can point me towards a supplier, or if any of our forum dealers can supply these it would be very much so appreciated.

    PM me if you can help! :lease:

    Whilst the amp is in bits I'm going to take the opportunity to modify the heatsink and install two temperature controlled 12V fans - it doesn't run that hot but I'd like it to run a lot cooler. I'll be doing the same to the 30.3 as well, as that runs stinking hot, and heat is the enemy of all electronic components!


    Thanks in advance to anyone who can help me.
     
  2. GaryB

    GaryB
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    Grandata in Wembley are usually good for this sort of thing. They do list the two transistors you're looking for in their online search but there's no facility to check for matched pairs/quads. They really know their stuff so it's worth giving them a call or drop them an email.

    Details at:

    http://www.grandata.co.uk/

    Tel:020-8900-2329
    email: grandata.ltd@btinternet.com

    I've been in electronics for more years than I care to remember and, whilst matched pairs are common, I've never heard of matched quads, although I'm sure they probably do exist, but with a decent quantity of transistors and a good transistor tester it should be possible to start with one matched pair and then match the gain (usually the most important) and other parameters to get two more to match, which is probably about the best you can hope for.
     
  3. fraggle

    fraggle
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    Thanks for the details.

    Unfortunately they don't have a clue. "I need matched pairs?" "Yes sir, we have two of each" "Err, no, I mean matched NPN and PNP" "Yes sir, there are 2 NPN and 2 PNP" "Ok, is there an engineer there I can talk to?" "no, we just sell the parts"

    Hopeless!

    Anyway, ordered 2 of each and I can just hope they're not too far out. At least they are genuine Toshiba parts.

    Now I've got to figure out how to set up the bias once I get it back together again, there is a preset pot in the middle of the push/pull quad output stages which must be it, but what to measure and where? Voltage across the output? Bias on the base of the finals? Current flow from the emitters?

    Actually I'm convinced the 30.3 needs setting up badly because it always runs hot, even when not being used, and I suspect the bias is set too high and allowing current to flow from +ve to -ve through all 4 finals.

    (yes its been donkeys years since I did this kind of stuff! :) )
     

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