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


    can you identify this board?

    Share

    prismstudios111

    Posts : 4
    Join date : 2013-05-18
    Location : Harvard, IL

    can you identify this board?

    Post by prismstudios111 on Sun May 19, 2013 12:27 pm

    I'm trying to identify this board on my dynaco amps. I picked these up from a guy on ebay. I have no experience with these amps and not sure if they are mk2's or mk3's. according to the layout of the tubes I would think they are mk3's? Is this correct? What i'm trying to do is bias them correctly according to the manual of the mk3. The left amp will only bias up to 1.03v and the highest I can get with the right amp is 1.3v. thats with the bias turned all the way to the right. I just ordered new 5ar4's hoping this will fix the bias problem. I am I going about this the correct way? Not sure because this has been modded for sure and I don't know if the original bias setting still applies. I can't find another pcb board the same that I have on the net. They hold two 6dj8's. Any comments will be greatly appreciated. I am new on here so it won't let me post any pictures. If you go on photobucket.com, search for "prismstudios" and look for folder "dynaco mk111". My pictures of the board are on there.



    Bob Latino
    Admin

    Posts : 2415
    Join date : 2008-11-26
    Location : Massachusetts

    Re: can you identify this board?

    Post by Bob Latino on Sun May 19, 2013 1:08 pm

    This may or may not be the case with your two amps but > If the selenium rectifier has been replaced with a diode on your two amps then you may have to drop the value of the 1000 ohm main bias resistor on a Mark III OR replace this resistor with a jumper wire to "expand" the range of the bias system on your two amps.

    I tried getting into your "prismstudios" photos on Photobucket but was unable. When you get posting privelages on the Forum, post photos of the inside wiring of one of your amps.

    Bob

    stewdan

    Posts : 161
    Join date : 2010-03-07
    Age : 78
    Location : Houston Texas

    Re: can you identify this board?

    Post by stewdan on Sun May 19, 2013 1:13 pm

    Hi --- I went to photobucket.com and logged in, then did a search on prismstudios. The bucket said it could not find prismstudios (the reponse had some graphical(?) characters before and after prismstudios)????

    Is "dynaco mk111" one "word" or is a space between the 2 parts?

    Please advise.

    Thanks

    stewdan

    Posts : 161
    Join date : 2010-03-07
    Age : 78
    Location : Houston Texas

    Re: can you identify this board?

    Post by stewdan on Sun May 19, 2013 1:45 pm

    Hi Again --- your question stated that your PCBs used 2 6DJ8 tubes. On the off chance that you have Curcio Modified Mk3's (which uses 2 6DJ8s), please check the following link ....

    http://www.dynaco-doctor.com/#DYNACO%20MARK-2%20&%203%20MONO%20POWER%20AMP

    and see if Curcio is what you have.


    prismstudios111

    Posts : 4
    Join date : 2013-05-18
    Location : Harvard, IL

    Re: can you identify this board?

    Post by prismstudios111 on Tue May 21, 2013 6:11 pm

    I'm not sure why my albums are not pulling up under a search. I'm there. Anyway,
    I did a little more research, and my transformer numbers match those of the manual of the Mark 3. So believe them to be mark 3's. The board is actually yellow in color just like the Curcio boards on thier site, but are set up a little different. It may be an older model of Curcio? Tonite i'll pull it apart and take pictures of the inside and see if I can see a selenium rectifier or not. I had it apart before and don't remember seeing one. A selenium rectifier is usually a square thin metal box right? I just spent some good money on a new matched quad of gold lion kt77's and bought a new matched pair of 5ar4's. The el34's that were in it before were no good anyway. So I thought by updating the el34's and the 5ar4's it would bias correctly but didn't think about the mods affecting the bias. I'm really curious how these are going to pair with my Altec Lansing A-7 VOTT's. I have only ran digital recievers through them with dissapointing digital harshness. Thank you for all your help, i'll post the underside when i'm a free man.

    stewdan

    Posts : 161
    Join date : 2010-03-07
    Age : 78
    Location : Houston Texas

    Re: can you identify this board?

    Post by stewdan on Tue May 21, 2013 8:44 pm

    Hi -- Yes, the selenium rectifier is usually a square shaped "box" thing with 2 terminals and a screw and nut thru the center. If you look at and download the Mk3 Manual that is on the Tubes4Hifi Website, you will see the selenium rectifier in the Pictoral Diagram. The Mk3 schematic shows it as a diode, but you need to look at the Pictoral Diagram, which shows the parts placement of the selenium rectifier.

    There is an updated version of the manual which Dynaco released for Mk3's that could run KT-88 Tubes, so there are some component differences shown in the Pictoral and the Schematic. In the updated manual, the selenium rectifier is replaced by a diode(1N4007 type) and is shown thusly on the Pictoral.

    The link to the updated Mk3 Manual is:
    http://www.the-planet.org/dynaco/Amplifier/Mark%20III.pdf

    Stew


    corndog71

    Posts : 454
    Join date : 2013-03-19
    Location : It can get windy here

    Re: can you identify this board?

    Post by corndog71 on Tue May 21, 2013 8:52 pm

    If it's a Curcio mod then the bias point might be different. Check the bias resistors connected to pins 1 and 8 and ground. If they measure 10 ohms then your bias point should be .50VDC. There should be a little pot on the driver board which will allow you to balance the bias between the tubes as well. Look for a wire from each tube bias resistor going to the test point socket and you may find a test point for each power tube.

    prismstudios111

    Posts : 4
    Join date : 2013-05-18
    Location : Harvard, IL

    Re: can you identify this board?

    Post by prismstudios111 on Sun May 26, 2013 1:07 pm

    O.k. finally got some pictures, here is the link to my album.
    http://s366.photobucket.com/user/prismstudios/library/Dynaco%20mk111
    I didn't see a selenium retifier. Would that have been where that yellow rectangle thing is? As soon as I get home, i'll check the bias resistors. Do you have to unsolder the resistors to check the measurements? Sorry for that i'm an amateur at best when it comes to testing electronics. Please let me know if there is anything out of the ordinary that you might see that should be replaced or fixed. I'm not looking for these to be original since they already have been modded, just the best setup for what I have. Like I said these are powering 2 Altec Lansing A-7's.

    tubes4hifi
    Admin

    Posts : 1292
    Join date : 2008-11-30

    Re: can you identify this board?

    Post by tubes4hifi on Sun May 26, 2013 1:17 pm

    those are Curcio boards, and your solution should be as Bob mentioned above in post #2, put a jumper across the 1K resistor.
    You do have a diode that replaced the selenium rectifier.

    corndog71

    Posts : 454
    Join date : 2013-03-19
    Location : It can get windy here

    Re: can you identify this board?

    Post by corndog71 on Sun May 26, 2013 6:42 pm

    Wow, that's quite a mess. I would gut those completely and rebuild them from scratch. Get some new chokes and boards and start over. It would be a great learning experience.

    I did just that with my first ST70. Bought it used with some non-original driver board in there. Lived with it for a bit but really was not impressed with how it sounded. I got the upgrade driver and "quad-cap" boards from Curcio and rebuilt it with more modern parts. I also replaced the power transformer with a newer and better-made version from Dynakitparts.

    I guess you could just try to get these running first but personally I think that's a job for someone with more experience.

    prismstudios111

    Posts : 4
    Join date : 2013-05-18
    Location : Harvard, IL

    Re: can you identify this board?

    Post by prismstudios111 on Tue May 28, 2013 4:02 pm

    Thank you corndog for the honesty...I already had in mind that eventually i'll be doing a complete makeover on these someday, just wanted to make the best of them at the moment, as long as they are o.k. to leave them they way they are without damaging other components. They still sound much better than the sony digital reciever I was using thats for sure.

    Sponsored content

    Re: can you identify this board?

    Post by Sponsored content Today at 12:33 pm


      Current date/time is Sat Dec 10, 2016 12:33 pm