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Groovy Unobtainium?

Discussion in 'Tape' started by Akai66, May 15, 2018.

  1. Akai66

    Akai66 New Member

    Messages:
    17
    When I first dived into restoring my Akai X-355 reel-to-reel I first read A LOT about the deck and the joys of resurrecting vintage audio equipment. Sadly, I had not done as much homework as I should have. I found out how difficult it can be to replace some of the components in a 50-year-old machine.

    I will jump into my first forum query by asking if anyone can answer this question: Has anyone tackled the re-capping of the X-355 "oscillator card"?

    This card would seem to exhibit engineering protocols that went out with the last Ice Age.

    The card contains three caps. Three odd-balls, I think.........

    100uf 6V electrolytic--+/-1% tolerance (!)

    .068uf 400V "plastic condenser"--perhaps a polystyrene cap?? +/-1% tolerance

    .01uf 400 "oil condenser" +/-1% tolerance

    I have a second X-355 machine that I keep for parts. I made a rookie mistake by replacing the oscillator card caps in the first machine with what I thought were OK replacements. Wrong. W-R-O-N-G.

    When I belatedly obtained the machine's service manual I quickly discovered how badly I had missed the mark.

    I have located some .068uf 400V 1% tolerance caps of the "oil and paper" type. Old, but in-spec. However, I question their stability compared to a plastic film cap.

    The 'lytic I have no idea how to replace.

    The .01 uf 400V "oil consenser" might be replaced by a second .068uf 400V +/-1%??

    Being that this is an oscillator unit we are talking about, I am hesitant to wander off of the original Akai design. Am I being too particular??

    CALLING ALL KHARMICS!!
     
    Last edited: May 15, 2018

     

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  2. audiojones

    audiojones Jonesin' for audio Subscriber

    Messages:
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    For the 100uf I’d just use a general purpose electrolytic rated at 25 volts, the other two I’d use film caps rated at the approppriate voltage. If the oscillator isn’t working I’d be more concerned about the two germanium PNP transistors on that board. It’s getting harder to find appropriate Ge’s these days, used to be common as dirt.
     
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  3. Akai66

    Akai66 New Member

    Messages:
    17
    Thanks for the response! Right off the bat, cool avatar! Picasso--The Musicians. A favorite of mine.

    The lytic is a 1% tolerance cap. That tolerance concerns me as I can't imagine finding a film cap rated at 100uf. Film would be my first guess if I ever hope to get close to the tolerance of the old lytic. Yeah, I'm stubborn! :crazy:

    I don't know about the oscillator card yet; I haven't fired it up. I really want to try to hit the mark the first time in re-capping the oscillator card assembly. Those 1% Akai tolerances on all of the caps is a red flag to me.

    Question: How stable would a 1960's Japanese film cap be after 50 years?

    Thanks again for your help! :thumbsup:
     
  4. audiojones

    audiojones Jonesin' for audio Subscriber

    Messages:
    7,056
    Location:
    Central NJ
    Personally I wouldn’t get too hung up on it, I’d just replace it with a 100uf 25 volt 5% ‘lytic and be done with it. Modern electrolytic caps are going to be much closer to their values than anything Akai was using back in the early and mid 60’s regardless of what the tolerance claims to be. Replace films with films if necessary (though they are usually pretty stable) and small value ‘lytics up to 1uf with film if you want to (though not really necessary in a machine like this). Larger value ‘lytics just get changed out with ones of the same value and slightly higher (but not too much higher) voltages.
     
    Last edited: May 16, 2018
  5. Akai66

    Akai66 New Member

    Messages:
    17
    Check! Thanks AJones. More research has revealed that I probably shouldn't have touched the oscillator card. I was told that the caps on the card are very likely "proprietary" in nature. For those not familiar with the term: They could have been manufactured by Placon (.068uf 400V non-polar) and Nichicon (the other two) expressly for Akai--and possibly others. Even if I got the "plastic" (I found out it is actually polyester film) cap and the other two right as per spec the card probably still wouldn't work right. I am going to use the intact card from the second machine and give that a whirl. I have been flatly told that the oil cap and polyester film cap are still, very likely, fine.

    I will take your comment about 60's versus modern lytics under advisement. I will keep it in mind and swap out the lytic.

    Why not use a 6.3V rather than the 25V you suggested? I suspect there may be a particular reason.:idea:

    You mentioned not to go too much higher than original cap voltage throughout the machine. What is the safety margin, generally speaking? I understand that, in the audio path at least, going too high can cause problems even though the capacitance rating is right on.

    Question: The amplifier uses BIG 1000uf 25V axial lytics. Modern versions are nowhere near as big. Will having longer, exposed leads (to make up for the lost cap size) present interference problems? -----If so.................

    Question #2: Should I shield the leads somehow?

    Question #3: What is best to use as shielding in this application?



    Thanks again for your input!
     
  6. Akai66

    Akai66 New Member

    Messages:
    17
    The clouds opened up....What I thought was an "F" rating for the oscillator card caps is actually Akai's seemingly screwy way of indicating "Farad"! So the card's caps are identified just like this: Plastic Condenser .068u F 400V Oil Condenser .01u F 400V .

    At other places in the service manual parts list (Power Block, Relay Block) no "F" is used at all. Neither is "mu-f". Hmmmm. Cap ratings, when used, are placed after the indicated voltage ratings. The only caps with ratings other than the apparently presumed 20% are mylars.
     

     

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  7. audiojones

    audiojones Jonesin' for audio Subscriber

    Messages:
    7,056
    Location:
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    I like to shield the leads on axials with wire insulation when that situation comes up. I just strip some insulation off of a piece of wire that is of the same approximate diameter and slide it over the cap lead wire before fitting it onto the board.

    I don’t generally use any caps below 25 volt rating because when they get that small they don’t usually hold up very well plus it’s an unusual voltage that your cap may not be available in anymore. Back then it was more of a cost saving issue, if the circuit only ran at 3 to 5 volts then they’d put a 6 volt cap in there (too close IMO but good enough back then). Component structure has changed a lot in the past 50-60 years.

    If a cap is actually in the audio path then use a low leakage low noise cap like Nichicon CEANL with voltage close to the same as existing (in other words if the original is a 6 volt then use a 25 volt unless a lower voltage is available for your specific application) or a film cap if it’s 1uf or below (in which case don’t worry about the voltage ratings or the polarity). Never go under the voltage rating but it’s fine to go over by a little in audio applications and by a greater margin in power applications.
     
    Last edited: May 17, 2018
  8. Akai66

    Akai66 New Member

    Messages:
    17
    Hey AJones--

    Check, check and check! Thanks for helping me out with this stuff!

    The illustration I used for Akai's cap spec layout is not really dramatic enough. The Farad "F" is way over to the right; away from the mu.
    XXu F XXXV. I am quickly finding out that there is a balance between what is going on in the service manual and what is really going on. I have scribbled in little notations in the manual as I have been going through the machine.

    This X-355 project has been quite satisfying. I love the "vibe" of the machine and the rather interesting automatic features. It is built like a battleship, but I am slowly realizing that the electronics are indeed "riding the edge" of spec in some places. They wanted $800 for the thing back in '65 and I have to believe all of the hand-soldered/wired guts certainly added to the overhead in a considerable way.

    I don't expect the machine to perform as well as a deck made later on, but I am the kind that wants to have a good, solid restored machine that is reliable and everything that it should be (and a little bit more don't hurt!) for its time. I am digitizing a big reel collection that I have slowly somehow amassed over the years. They have peculiar styles of music on them (many live performances) that are right down my alley. They date from 1955 all the way through to 1980. Even if I had a top-of-the-line r2r (in most everyone's opinion), the reels would not do the machine justice. You know what I mean.

    I am just waiting for the time when I can start running the reels and my wife asks me, "What...are...tape...reels....doing...in...the...oven???"

    I have replaced all of the bearings (easy to get) and motor start caps. Perhaps I made a mistake replacing the (metallized paper?) start caps with lytic cans? Oh well. When I latched onto the idea of a "total re-cap" I meant it! As with any rookie venture, you quickly find out what you don't have to do and what you shouldn't do! One thing I knew I wouldn't touch is the interesting multi-section cap linked to the auto-function timer. I could only find one very old mention of the QAK-1, and it that was vague and cursory.

    I have had to back-track with the electronics because of the aforementioned uninsulated/extended, twisted wire cap leads in the amp and the fact my friendly electronics store owner sold me a bunch of (what I understand to be) crappy Jackon caps mixed in with other brands that I would not have put in had I known the reputation and virtues of Panasonic, WIMA and Nichicon ahead of time.

    Everything has been cleaned and lubed. However, I think I will probably replace the damping grease that was in the in the pots--IF they check out OK in operation. Weird, but just that sort of final touch does make the pots feel more "professional"; more "precise".

    Thanks Again!
     
  9. audiojones

    audiojones Jonesin' for audio Subscriber

    Messages:
    7,056
    Location:
    Central NJ
    For motor run caps I find it's best to use polypro caps used for ceiling fans and the like (little black plastic box caps). The values are dead-on, they are super reliable and inexpensive plus they'll fit anywhere. The UF rating must be exact for the motor run caps, if they're off by even 1UF and the motor will run hot and speed will drag. To illustrate my point, the only difference between 50hz and 60hz operation when you flip the machine's cycle conversion switch is that 1UF is added to the value of the run capacitor. Probably the only capacitor in the machine that has to be dead-on no foolin' since it's responsible for keeping the motor windings properly synchronized to the line frequency.

    If you run into any of those awful defective back coated "sticky shed" tapes a food dehydrator is the best method for dealing with them. An oven thermostat won't regulate well at the low temperature needed to re-form them, and neither method will help with "dry tape" syndrome (lubricant dried up in the tape formula) which is more common with certain older brown tapes such as Sony PR-150.
     
  10. Akai66

    Akai66 New Member

    Messages:
    17
    Hey AJones--

    I will file the motor start caps info for further reference. The tape baking thing is getting filed away, too. Who knows what I will find in my mountain of reels?:idea:


    Thanks!
     
  11. audiojones

    audiojones Jonesin' for audio Subscriber

    Messages:
    7,056
    Location:
    Central NJ
    That’s the fun part! You’re welcome, good luck getting ‘er going again! :trebon:
     

     

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