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Mike's Stereo 20 refurbishment thread.

Discussion in 'classic' started by Mike P, Apr 23, 2019.

  1. Mike P

    Mike P pfm Member

    That all makes sense, I'll be sure to move it if I do fit a switch.
     
  2. Tony L

    Tony L Administrator

    Has anyone actually had the ‘magic resistor’ thing work and drop out? I like to think I’d get to the power switch in a fault scenario before anything got that hot! I guess it was designed in for the days when people had them tucked away out of sight in cabinets etc. Mine is right in front of me so I’d spot any red-plating or other valve lightshow even if I didn’t hear it.
     
  3. Mike P

    Mike P pfm Member

    The Russian K40y-9 paper in oil caps arrived today and have now been fitted.

    [​IMG]P1110146 by Michael Pickwell, on Flickr

    After fitting them it occurred to me that if the original big electros were still serviceable I could potentially give the amp a sneaky try. Too much temptation!

    I left the two big electros gently reforming at 12v for a couple of hours and then tested them.
    [​IMG]P1110141 by Michael Pickwell, on Flickr

    They obviously made 'em tough in those days.

    So, I couldn't resist firing it up. I connected it up to my 'sacrificial lamb' speakers and used an ipod as a source.
    [​IMG]P1110148 by Michael Pickwell, on Flickr

    It's alive!! I left it playing for about 1 hour and all is well, no magic smoke and no fireworks.

    Fortunately we're going away now for a few days so I won't have to fight the temptation to connect it to my Tannoy Ardens until after I get back, by which time I'll have the new F&T smoothing caps ready to fit.
     
    Wilson, John_73 and divedeepdog like this.
  4. John_73

    John_73 pfm Member

    Fabulous! Well done Sir!
     
  5. Mike P

    Mike P pfm Member

    Thanks John, I can't wait to try it with my Tannoys.
     
    John_73 likes this.
  6. Tony L

    Tony L Administrator

    Excellent stuff. If the big caps measure ok and there is no hum they are probably still functional! Still best to replace, though I know a lot of Japanese audiophiles try to keep their Leaks as authentic as possible with as many original components as are viable. I’m too cowardly/OCD for this by far, I need to know mine is bang in spec even if it has moved a little from original component types.
     
  7. toprepairman

    toprepairman Trade: HiFi repairs and servicing.

    If it works fine then I'd leave them in.
     
  8. Mike P

    Mike P pfm Member

    The new caps are just waiting to be painted in the colourmatched topcoat before being fitted. I'll report back with pics when they're done.
     
  9. snowman_al

    snowman_al pfm Member

    +1, if they work fine.
    Just make sure they do not heat up or get hotter than the chassis around them.
    You can do a simple leakage test if you pull all the valves out except the GZ34. Then switch on for a couple of minutes and measure the HT volts (say 330 volts), then switch off and see how long it takes to decay back to zero. The slower the decay the better. If it falls very quickly there is significant leakage and that is just extra current the mains transformer has to supply.

    Overlapped your post Mike. Replace and be sure... then keep the originals safe.
     
  10. Mike P

    Mike P pfm Member

    With no signs of misbehaviour connected to my test speakers I plucked up the courage to try the Leak in my main system driving my mk1 Tannoy Ardens. I used my Sony CDP-555ESD as a source which has a very good variable output.

    So how does it sound? Well, in summary it sounds absolutely wonderful! I can scarcely believe that a 58 year old 10w amp can sound so good. If it sounds any better with the new smoothing caps (and maybe some new valves) I'll be ecstatic.

    I'm away for a week or so now but I'll post details of the new smoothing caps and some beauty shots when I return.

    It might be time to start shopping for a decent passive pre and stocking up on valves.
     
    Taff63, John_73 and divedeepdog like this.
  11. Tony L

    Tony L Administrator

    They are just crazy good!
     
  12. divedeepdog

    divedeepdog pfm Member

    The 301 that came with it is the least used motor unit I've seen, if it wasn't for the B'stard dust bug I'd be passing it of as an SME :D
     
  13. Steve Taylor

    Steve Taylor pfm Member

    So would SME if it was sold to them!
     
  14. Arkless Electronics

    Arkless Electronics Trade: Amp design and repairs.

    I did say in a post a couple of weeks ago that the original smoothing caps, bizarrely, seem to never go wrong...:)
    Still in use in mine... but extra capacitance in parallel. I have a huge choke in the PSU of mine which isolates the GZ34 enough for me to put 220uF after the choke:)
     
  15. Mike P

    Mike P pfm Member

    I fitted the new smoothing capacitors today.
    [​IMG]P1110149 by Michael Pickwell, on Flickr
    Like Tony I took a bit of extra time to fill the groove that's on the capacitor side with a bit of car body filler. A couple of coats of primer followed by a few coats of colour and then a final few coats of clear lacquer finishes the job.

    The paint colour match isn't terrible but it's not brilliant either, though it certainly looks massively better than bright blue. The transformers are a markedly different shade than the chassis anyway.
     
    John_73 and Dowser like this.
  16. Tony L

    Tony L Administrator

    How is it sounding?
     
  17. Mike P

    Mike P pfm Member

    It's killing me but I haven't been able to listen to it yet and there's a baby sleeping upstairs so it's not going to happen today.

    I'll report back once I've given it a good listen.
     
  18. Mike P

    Mike P pfm Member

    To be honest it doesn't really sound any different with the new smoothing caps. That's fine by me as it already sounded great and just indicates that the old caps were still serviceable. I'm glad I changed them in any case, if only for peace of mind.

    I'm using the 8 Ohm setting at the moment and haven't experimented with the 4 Ohm tap.

    My next jobs are to sort myself out with a passive pre and a spare set of valves.
     
  19. a.palfreyman

    a.palfreyman pfm Member

    The colour looks close to that of the tx cans, just a bit denser / more flake. Nice.
     
  20. Mike P

    Mike P pfm Member

    The postie has just been....

    [​IMG]P1110151 by Michael Pickwell, on Flickr

    A matched quad of 6P14P-EV

    It seems to be generally considered that NOS Mullard are the best GZ34.

    What are the favourites for the ECC83s? Mullard? Brimar? Telefunken?
     

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