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    Getting ready to restore my pair of MK III's - questions

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    ViperZ

    Posts : 62
    Join date : 2010-03-26

    Re: Getting ready to restore my pair of MK III's - questions

    Post by ViperZ on Wed May 02, 2018 4:07 pm

    I know it's called strain relief. I just can't find the right one Sad. The hole is 9mm in diameter. The cord is round. All strain relief fittings are for flat cords at the local store, or for a bigger opening. I'll keep searching.
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    Peter W.

    Posts : 930
    Join date : 2016-08-07
    Location : Melrose Park, PA

    Re: Getting ready to restore my pair of MK III's - questions

    Post by Peter W. on Wed May 02, 2018 4:30 pm

    ViperZ wrote:I know it's called strain relief. I just can't find the right one Sad. The hole is 9mm in diameter. The cord is round. All strain relief fittings are for flat cords at the local store, or for a bigger opening. I'll keep searching.

    9mm..... Back in the day, Dynaco used the standard 2-wire line cord strain-relief, I believe that was based on a flat-sided 3/8" hole, so about 9.525mm. Maybe 9mm on the flattened side. It is interesting how choices drive choices, and those secondary choices might be quite troublesome. And you are in the position of either having to cut sheet-metal, develop an unsafe kluge, or create a modification that is neither necessary nor particularly useful - unless you are in a wet, salty environment. Then, I could *just* see the need.

    Writing for myself, I purchase basic quality US-made polarized line cords matching OEM otherwise, half-a-dozen at a time. So, if it came with 2, it gets 2. If it came with three, it gets three.

    That is as broad a hint as I will give at this time. Otherwise, the moderator(s) Might slap me down - with good reason.
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    ViperZ

    Posts : 62
    Join date : 2010-03-26

    Re: Getting ready to restore my pair of MK III's - questions

    Post by ViperZ on Wed May 02, 2018 6:09 pm

    Peter, all three of my Dynaco amps (ST-70 and MK-III), Dynaco used a grommet to protect power cord from being cut on the metal, then power cord was tied in a knot, so you wouldn't pull it out. There were no strain-relief fittings. Both of my MK-III have round holes, not modern flat-sided ones.
    Of course, I can easily go from 3-wire to 2-wire. Ground connection to chassis is just one of the transformer chassis bolts right beside the opening. I am also rewiring power switch in series with the fuse for the 3-wire change.

    I just hate ordering parts like that - weird that even a local parts store was sooo poor on strain relief selection Sad
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    ViperZ

    Posts : 62
    Join date : 2010-03-26

    Re: Getting ready to restore my pair of MK III's - questions

    Post by ViperZ on Wed May 02, 2018 6:25 pm

    Hm, anything 3-wire, even 18/3 would require 16mm round hole...
    http://www.essentracomponents.com.sg/images-line/pdfs/SRB.pdf

    So what, everyone who goes with 3-wire just ignores the code and doesn't use strain relief, or makes a bigger opening? I see some special cable grip on dynakitparts.com , and it works for 3/8" hole, which is 9.5mm - I guess, that's the hole that I have.
    https://www.dynakitparts.com/shop/power-cord-end-stop-kit/
    Looks like it uses cable tie to hold the power cord in place??
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    Peter W.

    Posts : 930
    Join date : 2016-08-07
    Location : Melrose Park, PA

    Re: Getting ready to restore my pair of MK III's - questions

    Post by Peter W. on Thu May 03, 2018 7:03 am

    ViperZ wrote:Peter, all three of my Dynaco amps (ST-70 and MK-III), Dynaco used a grommet to protect power cord from being cut on the metal, then power cord was tied in a knot, so you wouldn't pull it out. There were no strain-relief fittings. Both of my MK-III have round holes, not modern flat-sided ones.
    Of course, I can easily go from 3-wire to 2-wire. Ground connection to chassis is just one of the transformer chassis bolts right beside the opening. I am also rewiring power switch in series with the fuse for the 3-wire change.

    I just hate ordering parts like that - weird that even a local parts store was sooo poor on strain relief selection Sad

    OK - some history that may help.

    Up until Dynaco moved from Powelton Ave. to Jefferson Street, they had no factory. They occupied a three-bay garage with a couple of offices, a service bay and that was about it. "Factory Assembled" meant Drexel students on piecework, their cartons were packed in sheltered workshops and other consolidators from parts sent from many sources. Just like Henry Ford had the crates containing ignition coils for his Model T (in part from Atwater Kent, by the way) sized so that they could become floorboards, Hafler had his parts and sub-assemblies packed to fit into his cartons.

    What that means: No two 'factory assembled' units were the same. Piecework - meaning the assembler got paid if the unit worked. Sloppy, fast, painstaking or otherwise. And if an assembler ran out of strain-relief pieces of an evening, a grommet would do fine. And, you _will_ find that that hole is sized and shaped for a strain-relief however it arrived to you.

    Please use the correct parts, and please assemble the device as-designed. If everything else is done correctly, and if there are no failed parts, it is perfectly safe. If you really do want that extra level of safety, feed your system from a GFCI device.
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    Peter W.

    Posts : 930
    Join date : 2016-08-07
    Location : Melrose Park, PA

    Re: Getting ready to restore my pair of MK III's - questions

    Post by Peter W. on Thu May 03, 2018 7:06 am

    ViperZ wrote:Hm, anything 3-wire, even 18/3 would require 16mm round hole...
    http://www.essentracomponents.com.sg/images-line/pdfs/SRB.pdf

    So what, everyone who goes with 3-wire just ignores the code and doesn't use strain relief, or makes a bigger opening? I see some special cable grip on dynakitparts.com , and it works for 3/8" hole, which is 9.5mm - I guess, that's the hole that I have.
    https://www.dynakitparts.com/shop/power-cord-end-stop-kit/
    Looks like it uses cable tie to hold the power cord in place??

    I don't see a UR on that latter part. For what that is worth.

    The "Recognized Component Mark" is a type of quality mark issued by Underwriters Laboratories. It is placed on components which are intended to be part of a UL listed product, but which cannot bear the full UL logo themselves. The general public does not ordinarily come across it, as it is borne on components which make up finished products.
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    ViperZ

    Posts : 62
    Join date : 2010-03-26

    Re: Getting ready to restore my pair of MK III's - questions

    Post by ViperZ on Wed May 09, 2018 8:59 pm

    Peter, it's funny. The old amp (with cloth lead wires) had a 3/8" hole, where I had to use dynakitparts fittings - they hold the 3-18AWG cable very well. The newer amp (with more modern pvc? covered wires) had a proper 12.7mm hole with flat sides, where I installed a proper strain relief on the power cable.
    My newer amp also had an extra screw connection (70V?) on the binding posts (which wasn't even connected). So tubes4hifi binding post assembly didn't fit - I reused the original dielectric board and installed binding posts onto it.
    My newer amp also had an (extra) white wire sticking out of the output transformer, it was taped up, so I cleaned up the insulation and heatshrunk the end on that wire.

    Looks like I'm finished rebuilding. I'll double-check all connections with the meter tomorrow night, reinstall the tubes and will fire them up.

    Interesting that no input and output need to be connected to turn on the amps and do the initial bias adjustment. I'll leave the pots in the middle position to start with, as the manual recommends.






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    ViperZ

    Posts : 62
    Join date : 2010-03-26

    Re: Getting ready to restore my pair of MK III's - questions

    Post by ViperZ on Sat May 12, 2018 2:10 pm

    Put them back together, installed tubes, warmed them up without tube rectifier. Inserted rectifier, warmed up again, adjusted both sets to 1.56V (1.51V after an hour at good load).

    They sound pretty good with Carver C-1 preamp, but it feels like there must be some mismatch in this couple.

    I'll go fetch my PAS-3 and will start restoring it - electrolytic capacitors, rectifier replacement, LED instead of pilot bulb, and coupling caps on the outputs. If I'm adventurous enough, I'll also replace the RCA connectors on the back.



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    ViperZ

    Posts : 62
    Join date : 2010-03-26

    Re: Getting ready to restore my pair of MK III's - questions

    Post by ViperZ on Sat May 12, 2018 2:18 pm

    Oh, they have a dead-quiet background with 3-prong cords (the preamp has a 2-prong cord, and PAS-3 that I will use also has a 2-prong cord).

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