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


    New Build Questions

    Share
    avatar
    WireNut

    Posts : 67
    Join date : 2017-02-21
    Location : Twin Cities

    New Build Questions

    Post by WireNut on Fri Apr 13, 2018 1:47 pm

    Guys, I have a good start having built the VTA board, but wanted to start a thread for questions.
    Here is my first one:
    Do you take the nuts off the transformer before putting on the rubber spacers to mount it?

    avatar
    WireNut

    Posts : 67
    Join date : 2017-02-21
    Location : Twin Cities

    Re: New Build Questions

    Post by WireNut on Fri Apr 13, 2018 1:49 pm

    I used the little photo icon to imbed a photo bucket image of the nuts and it is not there?

    http://photobucket.com/gallery/user/CryoParts/media/bWVkaWFJZDoxNTUyMDcxNTM=/?ref=1
    avatar
    vtshopdog

    Posts : 114
    Join date : 2015-07-11
    Location : UT, USA

    Re: New Build Questions

    Post by vtshopdog on Fri Apr 13, 2018 5:58 pm

    The rubber grommets are intended to mechanically isolate the tranny from the chassis and mitigate transmission of vibration that might create microphinics in the tubes.  

    The nuts and bolts on the tranny hold the lamination stacks together and should be fully tight.  Loose nuts are likely to generate more vibrations as the laminations will rub against each other.  I have battled mechanical hum on my M125’s off and on, in general tightening the stack-lam bolts helps things, part of my once a year maintenance.

    So to answer your question,  assembly order is tranny with nuts and bolts fully tightened then rubber grommets then chassis with keeper nuts below the deck.  How much to compress the grommets is not clear cut issue.  At some point one can over tighten to degree that the rubber will be compressed enough to be ineffective.
    avatar
    WireNut

    Posts : 67
    Join date : 2017-02-21
    Location : Twin Cities

    Re: New Build Questions

    Post by WireNut on Sun Apr 22, 2018 4:03 pm

    Well, I got it all wired up and went to step on in the start up instructions. I installed three 12au7 tubes and nothing. In the trouble shooting part it says to check the voltage where the twisted pair comes in to the driver board, do you do that with the tubes in?
    I am including two photos of the wiring, front to back and visa versa. Please take a look and see if there are any errors you can spot- I have moved the on/off switch to the front & installed the digital bias meters- other than that it is as per instructions.
    Photo 1:
    http://illiweb.com/fa/pbucket.gif?sort=3&o=0

    Photo 2:
    http://illiweb.com/fa/pbucket.gif?sort=3&o=1

    Thanks for looking!
    avatar
    j beede

    Posts : 447
    Join date : 2011-02-07
    Location : California

    Re: New Build Questions

    Post by j beede on Sun Apr 22, 2018 4:12 pm

    Nothing... as in the 12AU7 filaments are not glowing?

    Do you have a clamp on current meter? If so what steady state current do you see when powered up? If you don't have one why not drive over to Harbor Freight and pick one up for $12 or so. It is a useful debug tool to have in your tool kit.
    avatar
    WireNut

    Posts : 67
    Join date : 2017-02-21
    Location : Twin Cities

    Re: New Build Questions

    Post by WireNut on Sun Apr 22, 2018 4:40 pm

    I have a Fluke 111 with attachments, so I am good. Do I test with the three 12AU7's installed or out of the sockets?
    avatar
    j beede

    Posts : 447
    Join date : 2011-02-07
    Location : California

    Re: New Build Questions

    Post by j beede on Sun Apr 22, 2018 5:01 pm

    Rectifier to remain out of socket for the following tests

    1) Power up with no tubes installed as a gross short test. Power down. If the fuse survived this gross shorts test on go to step 2. If the fuse failed stop testing and come back here.
    2) Install the 12AU7s only, power on and check for glowing filaments. Good glow then power down and go to step 3. No glow stop testing, check line fuse and come back here.
    3) Measure line current, power down. If line current is 100-300mA go to step 4. If line current was >300mA come back here.
    4) Install one output tube, power on and check for filament glow. Good glow then power down and go to step 5. No glow stop testing, check fuse and come back here.
    5) Install all four output tubes, power on and check for filament glow. Good glow then power down and go to step 5. No glow stop testing, check fuse and come back here.
    avatar
    WireNut

    Posts : 67
    Join date : 2017-02-21
    Location : Twin Cities

    Re: New Build Questions

    Post by WireNut on Sun Apr 22, 2018 5:18 pm

    Beede, thanks for the quick response. Do I test using the two spots on the board where the twisted wires were soldered?
    Also I powered it up like you suggested above, the fuse is OK but noting happened- it is like the unit is not getting power.
    This is how I wired it, the power cable comes in the chassis and the white is connected to a 17ga wire that goes to the switch, there is a 17ga wire that comes back and is connected to one of the black wires to the transformer, The black wire of the cable that comes from the wall A/C is connected to the top of the fuse holder, the switch was checked for continuity and passed, both wires to the black ones to the transformer were tested and passed.
    Here is a close up of how it is all connected:
    http://illiweb.com/fa/pbucket.gif?sort=3&o=0
    avatar
    tubes4hifi
    Admin

    Posts : 1463
    Join date : 2008-11-30

    Re: New Build Questions

    Post by tubes4hifi on Sun Apr 22, 2018 5:50 pm

    I'm not getting any images on your photobucket links, maybe the pages are protected?
    At any rate, is there some reason the VTA wiring diagram isn't simple enough to understand?

    avatar
    WireNut

    Posts : 67
    Join date : 2017-02-21
    Location : Twin Cities

    Re: New Build Questions

    Post by WireNut on Sun Apr 22, 2018 5:55 pm

    Thanks for the pretty diagram, I already have one, and followed it then rechecked it.
    I will check all the connections via the instructions again, then figure I have a bad transformer.
    avatar
    Bob Latino
    Admin

    Posts : 2652
    Join date : 2008-11-26
    Location : Massachusetts

    Re: New Build Questions

    Post by Bob Latino on Sun Apr 22, 2018 6:16 pm

    WireNut wrote:Thanks for the pretty diagram, I already have one, and followed it then rechecked it.
    I will check all the connections via the instructions again, then figure I have a bad transformer.

    Dave,

    Post a photo here of how you have the amp wired ..

    Bob
    avatar
    WireNut

    Posts : 67
    Join date : 2017-02-21
    Location : Twin Cities

    Re: New Build Questions

    Post by WireNut on Sun Apr 22, 2018 6:17 pm


    Lets see if this one will show up?
    avatar
    WireNut

    Posts : 67
    Join date : 2017-02-21
    Location : Twin Cities

    Re: New Build Questions

    Post by WireNut on Sun Apr 22, 2018 6:20 pm

    From the other angle:
    avatar
    WireNut

    Posts : 67
    Join date : 2017-02-21
    Location : Twin Cities

    Re: New Build Questions

    Post by WireNut on Sun Apr 22, 2018 6:46 pm

    Guys, I am not being rude if I don't respond anymore today, the last two days have been nice here and I am going to fire up the grill now... last week we had 17" of snow!
    More tomorrow.
    avatar
    WireNut

    Posts : 67
    Join date : 2017-02-21
    Location : Twin Cities

    Re: New Build Questions

    Post by WireNut on Mon Apr 23, 2018 7:58 am

    I got up early thinking about this- I thought it might be the power connector that goes into the wall.
    I took the connector apart and sure enough, the neutral wire was loose and would make contact sometimes. I must have tightened it on the insulation and when I turned the amp over to install the tubes it moved the wire enough to slip... anyway, it is clamped down now & I can continue with the tests. That would explain why I got power readings at first and later it seemed like it was not getting power.... because it wasn't.
    It is a nice connector even if it caused some issues:

    BNR_1

    Posts : 104
    Join date : 2013-06-11

    Re: New Build Questions

    Post by BNR_1 on Mon Apr 23, 2018 3:27 pm

    I am glad that you have figured out your problem. I am curious what is the purpose of the transformer that sits between the PT and choke?

    Thanks
    avatar
    WireNut

    Posts : 67
    Join date : 2017-02-21
    Location : Twin Cities

    Re: New Build Questions

    Post by WireNut on Mon Apr 23, 2018 4:04 pm

    That actually is the power supply for a pair of digital readout meters for the bias. I will include photos of that later as I blew the mains fuse when I turned it out of the neutral position on the switch. I am trying to figure out if I put a wire that came loose on the wrong pin when I installed it. The guy that sells them on Fleabay is pretty prompt with help.
    avatar
    WireNut

    Posts : 67
    Join date : 2017-02-21
    Location : Twin Cities

    Re: New Build Questions

    Post by WireNut on Mon Apr 23, 2018 4:15 pm

    OK, this is unique. I blew a fuse as mentioned above, when I went to install a new one the power cable was plugged in but the power switch was off. I was holding the chassis and got a 122v shock- is that normal or did I miss something else?
    avatar
    peterh

    Posts : 965
    Join date : 2012-12-25
    Location : gothenburg, sweden

    Re: New Build Questions

    Post by peterh on Mon Apr 23, 2018 4:30 pm

    WireNut wrote:OK, this is unique. I blew a fuse as mentioned above, when I went to install a new one the power cable was plugged in but the power switch was off. I was holding the chassis and got a 122v shock- is that normal or did I miss something else?
    120V is for kids :-) We use 230V here !

    The importance for safe working is everywhere. 120V is enough for bad things to happen.

    A few thumb rules when working with mains :
    - always unplug when working. IEC inlets makes this very convenient as the
    connector is where you are
    - two pole circuit breakers are an important safety item
    - fuses on both incoming is protecting you always
    - ground fault interrupter before the item in work is a good thing (Tm)
    - at the workbench there may be an advantage that the ground is left floating from
    the bench, provided that the worker is reasonable isolated ( no wet concrete floor, no
    grounded water pipes within reach)
    - use only one hand ! Keep the other in your pocket. This prevents current through the heart.
    - don't work alone, have someone nearby if something bad happens.

    Don't rush, think first grab later.
    avatar
    WireNut

    Posts : 67
    Join date : 2017-02-21
    Location : Twin Cities

    Re: New Build Questions

    Post by WireNut on Mon Apr 23, 2018 4:33 pm

    I should have read that before I put the fuse in :-)
    avatar
    tubes4hifi
    Admin

    Posts : 1463
    Join date : 2008-11-30

    Re: New Build Questions

    Post by tubes4hifi on Mon Apr 23, 2018 11:16 pm

    and I repeat !!

    - always unplug power when working.
    - use only one hand ! Keep the other in your pocket.

    I learned this about 55 years ago, once you get shocked, you won't forget (assuming you're still alive)

    BNR_1

    Posts : 104
    Join date : 2013-06-11

    Re: New Build Questions

    Post by BNR_1 on Tue Apr 24, 2018 4:03 pm

    Ouch that must hurt....but at least you are alive and able to share your experience.

    It is hard to see in your photos, but are your neutral and hot wiring both directly connected to your PT primaries via the fuse housing? I don't see the hot from your fuse to the switch.

    Generally, hot from the power cord to the rear end of the fuse housing and the side terminal of the housing goes to the switch. From the switch it goes to the PT primary (1). The neutral from the power cord goes to the PT primary (2).
    avatar
    WireNut

    Posts : 67
    Join date : 2017-02-21
    Location : Twin Cities

    Re: New Build Questions

    Post by WireNut on Tue Apr 24, 2018 4:36 pm

    I relocated my on/off switch to the front of the unit, that is why it does not look like most.

    buchela

    Posts : 46
    Join date : 2011-03-09

    Re: New Build Questions

    Post by buchela on Tue Apr 24, 2018 5:21 pm

    BNR :
    Why the fuse have to be before the switch ?, what am I missing

    audiobill

    Posts : 331
    Join date : 2014-03-13
    Location : Philadelphia

    Re: New Build Questions

    Post by audiobill on Tue Apr 24, 2018 6:21 pm

    With all respect, given the nature of your questions I recommend ripping out all your "upgrades" and build a stock unit. Then, one "upgrade" at a time add them until it fails again. Tried and true's the word.

    Sponsored content

    Re: New Build Questions

    Post by Sponsored content


      Current date/time is Tue Jul 17, 2018 11:45 am