The Dynaco Tube Audio Forum

Dedicated to the restoration and preservation of all original Dynaco tube audio equipment - Customer support for Dynaco VTA tube amp kits, all Tubes4hifi.com products and all Dynakitparts.com products


    Restoring a pair of Mark IV mono blocks

    Share

    arkivel

    Posts : 6
    Join date : 2009-11-11

    Restoring a pair of Mark IV mono blocks

    Post by arkivel on Mon Dec 21, 2009 2:21 pm

    Hi there forum. I just picked up a nice pair of Mark IV mono blocks. They are all original and have had no mods or repairs that I can see. They came with all the original Dynaco labeled tubes, original manuals, and they even had the original Dynaco boxes that they were shipped in - shipped to California from the factory in June 1960.

    I want to do a mild restoration on them before I power them up. The transformers are actually pretty shiny looking and the chassis and cages look very good. The amps are pretty original so it's probably a good idea to keep them that way. I definitely don't want to experiment with changing boards or anything like that at this moment so I'm just looking at changing the critical components.

    This would involve changing the quad cap, filter caps, sockets, board caps, selenium rectifier etc. I need a little help determining the correct value components to use. Does anyone offer a rebuild kit with caps and sockets?

    What value of quad cap would you recommend for a stock Mark IV?

    What value filter caps?

    What value board caps?

    Am I missing any other caps or significant components?

    Any and all help would be greatly appreciated. I'd also like to post a few pictures as this project progresses.

    thanks

    Bob Latino
    Admin

    Posts : 2377
    Join date : 2008-11-26
    Location : Massachusetts

    Re: Restoring a pair of Mark IV mono blocks

    Post by Bob Latino on Mon Dec 21, 2009 9:59 pm

    arkivel wrote:Hi there forum. I just picked up a nice pair of Mark IV mono blocks. They are all original and have had no mods or repairs that I can see. They came with all the original Dynaco labeled tubes, original manuals, and they even had the original Dynaco boxes that they were shipped in - shipped to California from the factory in June 1960.

    I want to do a mild restoration on them before I power them up. The transformers are actually pretty shiny looking and the chassis and cages look very good. The amps are pretty original so it's probably a good idea to keep them that way. I definitely don't want to experiment with changing boards or anything like that at this moment so I'm just looking at changing the critical components.

    This would involve changing the quad cap, filter caps, sockets, board caps, selenium rectifier etc. I need a little help determining the correct value components to use. Does anyone offer a rebuild kit with caps and sockets?

    What value of quad cap would you recommend for a stock Mark IV?

    What value filter caps?

    What value board caps?

    Am I missing any other caps or significant components?

    Any and all help would be greatly appreciated. I'd also like to post a few pictures as this project progresses.

    thanks

    Hi,

    What I would do is ..

    1. Replace the two quad caps with two Dynakitparts 550 volt quad caps.

    2. Personally, I would pull both driver boards and replace them with two new boards and parts sets (with metal film resistors) from Dynakitparts OR if you want upgraded boards check out the replacement Mark IV boards from tbes4hifi. The old boards had carbon composition resistors which have probably drifted from their original values in the 50 years they have been in service.

    3. Pull the original selenium rectifier and replace it with a diode. You can use a two lug terminal strip in the same hole that held the selenium rectifier. Place the diode across the two lug strip and then connect the red/black wire to the banded side. Also replace the two 50 uF electrolytic caps on the 5 lug terminal strip. Make sure that the positive end of each cap goes to lug #3 which is grounded. I know that this seems strange (positive to ground) but remember that the bias system has reverse polarity. If you get a tubes4hifi replacement driver board you won't have to do this because the tubes4hifi driver board has the bias system and the new bias capacitors on the driver board itself.

    4. I would replace the tube sockets with new octal tube sockets. The original sockets were cheap plastic sockets. Call Kevin at Dynakitparts. He has some nice octal sockets with cadmium plated pins.

    5. You may want to replace some or all of the wiring. Dynaco used 22 gauge solid core copper wire. I recommend 20 gauge (one size thicker wire) solid core copper wire. You can also use stranded wire - it's just a little harder to work with. Either PVC or Teflon insulation is fine. The PVC wire of today is usually "irradiated" and is of much better quality than the PVC wire of 50 years ago ...

    Good luck and keep us informed of your restoration ... Yes - Post a few before and after photos for us ...

    Bob

    arkivel

    Posts : 6
    Join date : 2009-11-11

    Re: Restoring a pair of Mark IV mono blocks

    Post by arkivel on Tue Dec 22, 2009 1:00 pm

    Thanks Bob!

    I'm curious about the tubes4hifi Mark IV board; does it have individual bias controls on the board?

    Bob Latino
    Admin

    Posts : 2377
    Join date : 2008-11-26
    Location : Massachusetts

    Re: Restoring a pair of Mark IV mono blocks

    Post by Bob Latino on Tue Dec 22, 2009 1:08 pm

    arkivel wrote:Thanks Bob!

    I'm curious about the tubes4hifi Mark IV board; does it have individual bias controls on the board?

    Hi,

    Yes - not only does it have the amp's complete bias system on board it also has individual bias controls for each output tube. Check the link below for more information.

    Tubes4hifi Mark III and Mark IV driver boards

    Bob

    Pooch

    Posts : 53
    Join date : 2009-12-01
    Age : 66
    Location : Wa

    What Bob said...

    Post by Pooch on Thu Dec 24, 2009 1:03 am

    I just finished doing the upgrade on my mk4s, using the tubes4hifi boards, larger multisection cap and silver plated, teflon coated 22awg wire and it's the best amps I have, so far ( Eico hf-81, Sherwood 5500,Golden Tube se-40 modded). The Eico has a real nice, euphonic sound and most everything sounds good tru it, but the upgraded mk4s sound cleaner, more accurate without giving any etched, edgy sound. Still sweet with all the detail.I'm using the Russian k-40 coupling caps.
    If it were me, I'd listen to the 4s with the original boards first, just to compare how good they can sound, modded with the new boards.
    Gordy

    Sponsored content

    Re: Restoring a pair of Mark IV mono blocks

    Post by Sponsored content Today at 7:59 pm


      Current date/time is Tue Sep 27, 2016 7:59 pm