Yamaha M-70 Thread

Discussion in 'Yamaha' started by Bratwurst7s, Jan 17, 2018.

  1. Oldsansui441

    Oldsansui441 AK Subscriber Subscriber

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    Those RCA and speaker terminals look great, which RCA's do you need to replace? Last night l just finished installing binding posts on the M-50, not as nice as the terminals you chose but came out nice all the same.
     
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  2. avionic

    avionic " Black Knights " Subscriber

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    I´ve had my eye on one of those. I have a dedicated duty for it. And Japanese 100V MX-2000.
     
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  3. Oldsansui441

    Oldsansui441 AK Subscriber Subscriber

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    Can a variac be used as a full time power supply (set at any voltage) or are they only designed for shorter term test purposes?
     
  4. avionic

    avionic " Black Knights " Subscriber

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    We use them at work for vibrator bowls for mini vial capping machines and syringe unscramblers running 24-7 at a constant value. I have absolutely no reservations about using one for my intended App.
     
  5. Oldsansui441

    Oldsansui441 AK Subscriber Subscriber

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    Thanks avionic, l was just curious having never owned one.
     
  6. brutal

    brutal YamaHoarder

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    I picked up an HP 339A for not too much money years ago that seemed to work OK the few times I used it. But of course, buying old equipment on ebay is always a crap shoot.
     
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  7. avionic

    avionic " Black Knights " Subscriber

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    HP 334A here.
    They are handy.
     
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  8. Bratwurst7s

    Bratwurst7s In The Frying Pan Subscriber

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    Huh. This learning curve thing can be tough sometimes. Especially at my age.

    ebay wise it's pretty slim pickins here, and as brutal said above it's always a crap shoot. There's a really beat up looking HP331a in Poland for around €100 with shipping. Everything else is crazy expensive.

    I can maybe swing that QuantAsylum QA401 mentioned in the thread that Oldsansui441 linked. It would be a real budget stretch but if it can do everything needed I'd rather buy something new than throw the dice with ebay. I figure I'd be looking at about €600 by the time that I got it past the friendly Customs people.

    So I'm inviting comments about the QA401 as to it's usefulness for what I need. It's software probably needs Windoze to run, I'll have to look at that. I have 1 laptop dedicated to W7 so that would have to work. I'll never buy another MS product in my remaining lifetime if I can help it.

    Cheers,
    James

    edit: On the other hand, no. After thinking it over a bit more rationally I'd have to be nuts to spend that kind of money for a Distortion analyzer. I could buy an MX-1 for that kind of money.

    I'll look into the pc/software/sound card direction. Or simply wait, not touch those zdr pots and think the whole thing over.
     
    Last edited: Apr 7, 2018
  9. Bratwurst7s

    Bratwurst7s In The Frying Pan Subscriber

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    The RCA's are for the input jacks.

    Do we get to see photos of the M-50? Or perhaps a thread? :)

    Cheers,
    James
     
  10. Oldsansui441

    Oldsansui441 AK Subscriber Subscriber

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    Haha, l must have been a bit tired when l asked that stupid question earlier today. Of course there is only one pair of inputs on your M-70 power amp. I have been playing with the C-50 also and must have had my place all over the head :rolleyes:.

    Sure l will take a photo for you.

    I will be very interested to hear how you go with the M-70 distortion adjustment.
     
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  11. Bratwurst7s

    Bratwurst7s In The Frying Pan Subscriber

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    So will I. ;):(:)

    James
     
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  12. OMGCat!

    OMGCat! AK Subscriber Subscriber

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    I've got the Quantasylum QA400 and it does run on windows.
    Mine is the older, low input power model so I have to use a differential probe to run it on loudspeaker amplifiers. I honestly haven't used it much at all so I can't really give any pluses or minuses.
    I really need to scoop out some time to sit down and really figure out how it works. Seems like a pretty useful tool from reading some of the threads where people used it.
     
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  13. Bratwurst7s

    Bratwurst7s In The Frying Pan Subscriber

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    Thanks for the input! It really looks like a nice tool. At ca €400 I could probably convince myself to buy it. But by the time $64 is added for shipping and another 19% VAT (which the friendly people at Customs include the shipping costs to calculate) I'm looking at around €600. And I just can't see that.

    So, what do I do? I think that for the moment I'm going to push this step off until later. While I know that the issue won't go away if I ignore it at the same time I think that if I leave my fingers off of those trim-pots at least I won't make anything worse and I can take some time to decide and look for a more cost effective solution.

    I did some looking at the HP 331/332/333/334 series. There are some of them around for €200-250 with shipping. But I'm not understanding something. The specs show a best THD resolution of 0.01% with these units. I don't understand how that can work to measure an amp with a THD of 0.002%. So I don't picture buying one without more information/knowledge.

    Cheers,
    James
     
  14. Bratwurst7s

    Bratwurst7s In The Frying Pan Subscriber

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    Today I replaced those 39k resistors with some Vishay metal film and raised them up off of the board a bit. 71-RN60D3902F.
    Then I took the one original 56ohm fusible on the bottom of that row from the right channel and moved it down to replace the unknown type replacement in the left channel so that at least R181-182 are the same. Then I put 2 of the RN's in 56 ohm in the fusible positions R179-180.
    Also got the MV12 diodes replaced.

    DSC05221.jpg DSC05224.jpg

    Cheers,
    James
     
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  15. Bratwurst7s

    Bratwurst7s In The Frying Pan Subscriber

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    After dealing with those resistors I replaced the idle current trim pots with Bourns 652-3299Y-1-501LF. I measured the old trimmers after removing them and pre-set the new ones to the old values.

    DSC05226.jpg DSC05227.jpg DSC05228.jpg

    Lead spacing on the old pots is 5x10mm and the new ones 5x5mm but the leads are long enough to bend and spread the spacing.

    I haven't touched the ZDR trimmers and won't until I decide what to do about an analyzer.

    After that I started with re-flowing the connections in the board, about 25% are done now.

    Cheers,
    James
     
  16. Bratwurst7s

    Bratwurst7s In The Frying Pan Subscriber

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    I was looking over the main pcb just now, checking out the area's that I'm going to re-flow today. I just spotted another ring crack. R270, a 0.1ohm/5w resistor directly in the right channel signal path. That can't have been doing the amp any good.

    DSC05232.jpg

    Middle of the photo, just to the right and above the big fat wire connection and directly to the left of the cable tie. I'm going to have to be sure/careful to re-flow every single connection.

    Cheers,
    James
     
    Last edited: Apr 8, 2018

     

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  17. Oldsansui441

    Oldsansui441 AK Subscriber Subscriber

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    The one l can see is to the left of the cable tie?. I feel for you as l have just spent hours reflowing about half of the joints on my pair, that's the one annoying thing with these early 80's Yammies, those damn dry soldered joints everywhere:thumbsdown:. Did you also find some on the meter board LED's?
     
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  18. Bratwurst7s

    Bratwurst7s In The Frying Pan Subscriber

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    Oops! Yes, that would be the left side of the tie. You would think that after 8 years in the military I'd be able to remember which left is the right one. (post edited, thanks for pointing that out)

    I haven't attacked the meter board yet. I'm saving that section for last. I also bought a couple of different LEDs for potential bulb replacements. That's one of the reasons that I bought the 30vdc bench power supply. I can use it to mock up a led+resistor and check the brightness before installing them.

    Cheers,
    James
     
  19. Oldsansui441

    Oldsansui441 AK Subscriber Subscriber

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    Ah, fair enough. Yes that bench power supply will be be super handy for that purpose.
     
  20. Bratwurst7s

    Bratwurst7s In The Frying Pan Subscriber

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    For the LED's I used an online calculator and came up with 430 to 510 ohms to reduce the power from 12v to 3v/20mA. I bought some 510 and 470 ohm.

    For the first test I tried the round nose 60° LED that will be for the power switch and protection indicator. 510 ohms gave me 2.976v at the LED and 470 ohms gave me 2.987v.

    DSC05235.jpg DSC05236.jpg DSC05238.jpg

    The last photo is with the LED shoved into the rubber glove only as far as the flange on the end of the LED. I'll have to sand off the flange to get the thing all the way in the glove. This is with the 470 ohm. I'll have to test this in the dark with the LED all the way in to see if it will be too bright.

    Cheers,
    James
     

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