Sanyo Plus Series P55 - condition unknown

Discussion in 'Dollars and Sense' started by 62vauxhall, Aug 10, 2018 at 5:20 PM.

  1. 62vauxhall

    62vauxhall AK Subscriber Subscriber

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    I may have just spent $10 on a doorstop or got a good deal on a 100 WPC power amp - Sanyo Plus Series P55.

    Never seen one of these let alone found one before so it was intriguing. Had to retrieve it from the top shelf in a reclaimed building material store and it's quite heavy despite being fairly compact.

    A while ago I swore off buying vintage gear to rehabilitate because I have trouble parting with stuff I've spent time fixing. Yesterday I walked away from a Yamaha CX-830 pre-amp and Pioneer A-7 integrated for $50 each. But I could not ignore a fairly scarce power amp for ten bucks.
     

     

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  2. saunadog

    saunadog Well-Known Member

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    706
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    For that price, I think you stole it! Plus Series is great stuff. I'd add "please keep it quiet", but the word has long been out on AK about this series.
     
  3. RichPA

    RichPA Don't drive angry Staff Member Super Mod Subscriber

    If you can get it working, that's a very nice amp.
     
  4. SoCal Sam

    SoCal Sam Lunatic Member

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    Dual transformer MOSFET, if memory serves. Nice score for $10.
     
  5. 62vauxhall

    62vauxhall AK Subscriber Subscriber

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    Well, at the moment it's a door stop. Brought it up with a variac and DBT and it's got issues. Will next be pulling and checking the output transistors and see what the DBT does with them out.

    Most likely be posting soon in the Solid State forum looking for help.
     
  6. blhagstrom

    blhagstrom Mad Scientist, fixer. Subscriber

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    If memory serves, you do not want to use a Variac or dim bulb on a MOSFET amp.

    MOSFET is a different animal.
     

     

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  7. 62vauxhall

    62vauxhall AK Subscriber Subscriber

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    After reading your post, I did a hard start. What had been happening when raising voltage with the variac was nearly all LED segments on both meters were solidly lit. Eliminating the variac, DBT and doing a hard start, the LED's all lit briefly then receded so only the first one stayed on.

    I did not realize MOSFET amps were treated differently. Only had one other MOSFET before and did not have to do a thing to it,

    I'm going to start that thread in Solid State as the right channel DC offset is high at over 150mv while the left is about 11mv. Accessing these PC boards does not look easy. Even after consulting the service manual, getting the case off to the degree that I have was a chore.
     
  8. ivandezande

    ivandezande Super Member

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    I had the C55 preamp and it was good gear. Good luck fixing her.
     
  9. 62vauxhall

    62vauxhall AK Subscriber Subscriber

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    It seems there is no need to post about problems in the Solid State forum after all.

    The lopsided DC offset reading weas due to adjustment pots in need of cleaning. As per the service manual, measuring bias voltage requires an 8 Ohm 100 watt (wtf?) resistor across the speaker terminals. I used a 25 watt because I had one. Bias is now at the specified ~10mv.

    There was also a 2nd adjustment explained in the service manual - Power Stage Current Adjustment. The goal for that was adding together voltages measured across two cement resistors (per side) so they total 50mv.

    DC offset is now 35 mv on right channel and 17mv on left. I can live with that.

    There are two things that need fixing. The right side terminal of speaker system A is not working (right side speaker system B is fine) and one of the input jacks is a bit loose. I think someone had one of those interconnects with the mondo tight RCA plugs and partially extracted the jack's outer barrel when pulling the plugs.

    So after spending a bit of time fiddling and a brief listen, I am satisfied this amp was a bargain for $10.

    And I learned something from blagstrom - that MOSFET amps get treated differently.
     
    Last edited: Aug 11, 2018 at 7:40 PM

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