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    Separate Driver Board Cage

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    AudioKMan

    Posts : 7
    Join date : 2014-06-07

    Separate Driver Board Cage

    Post by AudioKMan on Sun Jun 15, 2014 10:13 am

    All,

    I've just completed a Bob Latino VTA ST-70 kit.  I still have a couple weeks before I've collected the tubes and speakers so I'll share more of my experience once I've had a chance to hear the set up.  In the meantime, this is one of my first posts to this forum.  I really like the look of the original ST-70 but I am looking for options to cover the driver board (in my opinion, the driver board is the most "kit" looking part of the amplifier, everything else is gorgeous).

    So, I've found a handful of pics (3 in fact) of examples of a driver board cage.  The first two are my favorite and have been provided by Bob showing the original factory-assembled ST-70 that supposedly included a driver board cage during some years.  Of course, with the updated VTA board with 3 driver boards this option won't work.  Does anybody know where I could get a stainless steel version for a VTA driver board?

    The third pic is another example of a home-designed option.  I don't really like it since it completely covers the tubes and I don't think the metal mesh is really consistent with the vintage style of the ST-70.








    Cheers!
    AudioKMan


    Last edited by AudioKMan on Fri Jun 20, 2014 2:37 pm; edited 1 time in total

    j beede

    Posts : 316
    Join date : 2011-02-07
    Location : California

    Re: Separate Driver Board Cage

    Post by j beede on Sun Jun 15, 2014 12:46 pm

    I like #3. Anyone know of a source? I think I will have to build a pair for my Mk IIIs.

    AudioKMan

    Posts : 7
    Join date : 2014-06-07

    Re: Separate Driver Board Cage

    Post by AudioKMan on Sun Jun 15, 2014 1:00 pm

    j beede wrote:I like #3. Anyone know of a source? I think I will have to build a pair for my Mk IIIs.

    j beede, here's the website I found #3: http://www.canuckaudiomart.com/forum/viewtopic.php?f=9&t=9882&start=30

    Quoted construction details of #3:

    "The "mini-cage" is made from an aluminum alloy mesh screening that my friend had on hand, and is a type of "fold-over" construction - closed on all sides. The bottom edges are lined with brass L-shape to give it rigidity. So there are no ferrous materials in it. Hopefully that means that it won't affect the sound at all... "

    sKiZo

    Posts : 1285
    Join date : 2013-04-01
    Location : Michigan USA

    Re: Separate Driver Board Cage

    Post by sKiZo on Sun Jun 15, 2014 1:43 pm

    Was playing around with a "steampunkt" design when getting ready to build ...

    (A round of applause for photoshop ... clap clap ...)



    That would have been a simple cage made of brass rod stock with decorative screen brazed to the rod. Polish it up good, maybe a coat of paint ... Leave a couple of the vertical rods long and add a couple locator holes in the chassis to keep it from wandering around.

    I eventually went with Plan B ...

    AudioKMan

    Posts : 7
    Join date : 2014-06-07

    Re: Separate Driver Board Cage

    Post by AudioKMan on Sun Jun 15, 2014 4:27 pm



    Great photoshop work!  But maybe harder executing Smile  What ended up being "Plan B"?

    sKiZo wrote:Was playing around with a "steampunkt" design when getting ready to build ...

    (A round of applause for photoshop ... clap clap ...)



    That would have been a simple cage made of brass rod stock with decorative screen brazed to the rod. Polish it up good, maybe a coat of paint ... Leave a couple of the vertical rods long and add a couple locator holes in the chassis to keep it from wandering around.

    I eventually went with Plan B ...

    AudioKMan

    Posts : 7
    Join date : 2014-06-07

    Re: Separate Driver Board Cage

    Post by AudioKMan on Sun Jun 15, 2014 7:06 pm

    So now I'm thinking I could build a driver board cage myself (as shown on the original ST-70-A).  Seems doable for ~$60 (I'd have to purchase a small bending brake and sheet metal--I should have everything else needed).  Here's the tool list--maybe not yet complete:

    Tools Needed:

    • Drummel to cut steel


    • Bending BrakeExample Break


    • small piece of perforated sheet metal


    • soldering iron and solder wire to cold solder joints


    • rubber material to cover bottom edges (to prevent shorting and scratching of VTA board)


    • tool to cut circular holes on top of cage (not yet sure what this is)


    • 3 thin metal rings to attach to top of cage around driver tube holes




    AudioKMan


    Last edited by AudioKMan on Fri Jun 20, 2014 3:07 pm; edited 1 time in total

    sKiZo

    Posts : 1285
    Join date : 2013-04-01
    Location : Michigan USA

    Re: Separate Driver Board Cage

    Post by sKiZo on Sun Jun 15, 2014 8:05 pm

    Here's a nice little brake for the hobby shop ...

    http://www.harborfreight.com/18-inch-bending-brake-39103.html

    I'd still drill a couple locator holes to keep the cage where it belongs, Then, instead of rubber edging, maybe add legs and leave those a little long. Add some small rubber washers to those to keep it proud of the chassis. Just bend the bottom edge of the cage panels in to dress and stiffen them.

    And here's Plan B as requested. Somewhat different from the Steampunkt design:



    I mounted all the big caps under the board and adjusted the length of the mounting studs to get the right height for the tubes.



    Also swapped out the bias adjusters for some pots - you can see those along with test points at the sides of the top plate. Bit more work, but I figure it was worth it.

    AudioKMan

    Posts : 7
    Join date : 2014-06-07

    Re: Separate Driver Board Cage

    Post by AudioKMan on Sun Jun 15, 2014 9:14 pm

    sKiZo--Very nice work, both my wife and I are impressed.  It matches quite nicely with your tuner in the shelf below.  It looks like a VTA ST-120 "engine" with the chassis being your handiwork?  Do you happen to have any complete underside pics?  Did you salvage some of the parts from vintage amps (dials, meters, etc)?  I could see how these mods could become addictive. . .


    sKiZo wrote:Here's a nice little brake for the hobby shop ...

    http://www.harborfreight.com/18-inch-bending-brake-39103.html

    I'd still drill a couple locator holes to keep the cage where it belongs, Then, instead of rubber edging, maybe add legs and leave those a little long. Add some small rubber washers to those to keep it proud of the chassis. Just bend the bottom edge of the cage panels in to dress and stiffen them.

    And here's Plan B as requested. Somewhat different from the Steampunkt design:



    I mounted all the big caps under the board and adjusted the length of the mounting studs to get the right height for the tubes.



    Also swapped out the bias adjusters for some pots - you can see those along with test points at the sides of the top plate. Bit more work, but I figure it was worth it.

    sKiZo

    Posts : 1285
    Join date : 2013-04-01
    Location : Michigan USA

    Re: Separate Driver Board Cage

    Post by sKiZo on Sun Jun 15, 2014 10:42 pm

    While pondering my build, I decided I wanted more room for the big bottles, easier access to bias adjustments, bias meters, and dual volume pots so I could also balance the channels. Long as I had the room, I took the opportunity to hide the multi-cap and put in some larger chokes.

    CAUTION > NAKED PICTURES!!





    Wiring around the meters is pretty sloppy, but I went thru several versions of the circuit before I got them working properly. I do plan to clean that up one day, and at the same time, change out the bias pots for some 10 turn precision pots ... the ones I used are a might bit twitchy for my tastes.

    The meters are handy for doing quickie spot checks when I turn the amp on. They're surprisingly close, but I still use a VOM to do actual settings as it's more accurate.

    I built the case myself from an original design, using African cherry. That's the natural color. The final finish is just a couple coats of Watkins Poly run on. Kudos to Front Panel Express for the top plate ... I used their free software to lay out the panel, then just hit the buy button. Bit pricey, but hey, I'm worth it ... geek 

    The meters are Velleman and came from eBay. Really nice units for $10 each. The Mallory pots and scales were stashed for many years in the parts bins. The bias pots are vintage Fender, and  the chokes are Triad C17s ... here they are compared to the ones supplied with the kit ... those are more than adequate for the job, but as long as I had the room ...



    Other than that, it's pretty much a stock ST120.   ;-}

    AudioKMan

    Posts : 7
    Join date : 2014-06-07

    Re: Separate Driver Board Cage

    Post by AudioKMan on Mon Jun 16, 2014 7:54 am


    sKiZo,

    Thanks for the great ideas. Ok, I admit it's a bit more than just a separate driver board cage but it gives me some great ideas and inspiration for my next amp. The good news is that I can spend much more time on amp #2 since amp #1 will be up and running (don't stop the music)! Thanks again!

    AudioKMan

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