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


    My new ST-120A custom amp chassis

    Share

    baddog1946

    Posts : 304
    Join date : 2010-02-03
    Location : Costa Rica

    My new ST-120A custom amp chassis

    Post by baddog1946 on Sat Oct 22, 2011 5:05 pm

    Hi All:
    This is my latest DIY project:

    I finally figured out how to post images the one shown follows the original 2 piece ST-70 chassis format closely. The other on my photobucket link is a one piece chassis made for attaching cocobolo wood sides.

    I will be doing the wood side model first and will post more photos of this build now that I know how to do it soon and hopefully of the other one right after that.

    My new custom ST-120A (Aluminum chassis) amps are designed with "Front Panel Express" use a piece of aluminum plate (2.5 mm, thick) both are similar in layout to the Dynaco/VTA chassis on top but a little bigger and deeper to accommodate the bias meter and the caps on the driver board which are mounted on the bottom side of the driver board. I plan to use 3/8" solid Cocobolo slabs for the sides.
    The driver board itself is offset so the tops of the tube bases are flush with the top. Only the driver tubes and the holes for the bias adjustment are showing through the top.
    Everything else is 100% VTA/LATINO/Dynaco parts and layout.
    I will be buying the parts from Bob as soon As I have the plate back from Front Panel Express in a couple of weeks. Top plate chassis for the wood side cost was $137.43 US.



    Last edited by baddog1946 on Wed Nov 16, 2011 7:26 pm; edited 19 times in total (Reason for editing : typo mistakes from a sticky keyboard and I finally figured out how to post images so I had to edit the text as well.)

    Bob Latino
    Admin

    Posts : 2374
    Join date : 2008-11-26
    Location : Massachusetts

    Re: My new ST-120A custom amp chassis

    Post by Bob Latino on Sat Oct 22, 2011 7:20 pm

    Hi George,

    You did a real nice redesign and modernization of the VTA ST-120. You can tell a lot of thought was put in to the layout. You only have one triode/pentode switch and the original VTA ST-120 has TWO DPDT triode/pentode switches - one for each channel. You can do the switching with one switch though if you use a 4PDT switch. I am asuming that is what you had in mind ..

    Keep us informed on how the project progresses .. maybe take some photos along the way ..

    Bob

    baddog1946

    Posts : 304
    Join date : 2010-02-03
    Location : Costa Rica

    Re: My new ST-120A custom amp chassis

    Post by baddog1946 on Sat Oct 22, 2011 8:17 pm

    Hi:
    Thanks Bob, as soon as I get the chassis back I will start ordering all the components to go in it from you and try to photo document the build as I go.
    I appreciate your support. I did use intend to use a 4PDT switch for the triode/pentode switch setup but I want to keep the switch size as small as possible and am still looking for a good one. Any suggestions?
    cheers
    Baddog1946

    quad

    Posts : 14
    Join date : 2010-11-25

    Re: My new ST-120A custom amp chassis

    Post by quad on Sun Oct 23, 2011 11:01 am

    Your FPE top plate is looking great. Look forward to the final result.
    For my custom chassis for the VTA board, I had to
    diverge from the stock Dynaco design to accomodate toroidal
    transformers from Trafomatic.
    A pic here -



    baddog1946

    Posts : 304
    Join date : 2010-02-03
    Location : Costa Rica

    Re: My new ST-120A custom amp chassis

    Post by baddog1946 on Sun Oct 23, 2011 4:10 pm

    Hi Quad:
    Nice job! Where did you buy those torroid trannies with the covers? Is the chassis aluminium or painted steel?

    cheers
    baddog

    tubes4hifi
    Admin

    Posts : 1261
    Join date : 2008-11-30

    Re: My new ST-120A custom amp chassis

    Post by tubes4hifi on Sun Oct 23, 2011 9:15 pm

    Baddog - very nice, looking forward to actual photos.
    Quad - your project reminds me of one I did 4 years ago, and wound up selling

    quad

    Posts : 14
    Join date : 2010-11-25

    Re: My new ST-120A custom amp chassis

    Post by quad on Sun Oct 23, 2011 10:24 pm

    baddog1946 wrote:Hi Quad:
    Nice job! Where did you buy those torroid trannies with the covers? Is the chassis aluminium or painted steel?

    cheers
    baddog

    Thanks! Smile
    The chassis is painted steel.
    I got the Trafomatic set from Boris Sasic of Engineering Vista, in NY.


    Tom

    Posts : 166
    Join date : 2011-04-04

    Re: My new ST-120A custom amp chassis

    Post by Tom on Mon Oct 24, 2011 8:17 am

    SWEET!!!

    I hadn't even thought of torroids
    and <$150 is great for a custom chassis.

    This just keeps getting
    better and better!

    Very Happy


    davidness

    Posts : 39
    Join date : 2010-09-15

    ST-120A

    Post by davidness on Mon Oct 24, 2011 11:58 am

    I like the layout. Wood sides sound great, too.

    I know next to nothing about the circuit, but I was once told that the circuit (and the aesthetics/symmetry in general) might be improved with a second rectifier tube. Your thoughts?

    baddog1946

    Posts : 304
    Join date : 2010-02-03
    Location : Costa Rica

    Re: My new ST-120A custom amp chassis

    Post by baddog1946 on Mon Oct 24, 2011 12:51 pm

    I think Bob has it dialed in when he recommends a Weber WZ68 solid state rectifier which has plenty of current flow even for the KT120's running at 60 millvolts. I plan to install the relay delay module he sells which should stabilize things further.
    There is a point of over complication and overkill that goes against the KISS principle. the less you have in the signal path the better.


    Bob Latino
    Admin

    Posts : 2374
    Join date : 2008-11-26
    Location : Massachusetts

    Re: My new ST-120A custom amp chassis

    Post by Bob Latino on Mon Oct 24, 2011 1:20 pm

    davidness wrote:I like the layout. Wood sides sound great, too.

    I know next to nothing about the circuit, but I was once told that the circuit (and the aesthetics/symmetry in general) might be improved with a second rectifier tube. Your thoughts?

    Hi David,

    The ST-120 works fine with a single GZ34 TUBE rectifier - BUT - in the ST-120 you are near the flow limit (250 milliamps) of a GZ34. I feel that the ST-120 does work better with the Weber WZ68 (450 milliamp flow limit) IF ...

    (1) your speakers present a complex load to the amp and, as such, are hard to drive
    (2) your speakers are relatively inefficient
    (3) you play the amp loud a lot

    With the ST-120 you have a CHOICE of tube or solid state rectifier and the change is easy - just take out the tube rectifier, install the Weber and rebias the amp.

    Bob

    jdm

    Posts : 45
    Join date : 2011-04-04

    Re: My new ST-120A custom amp chassis

    Post by jdm on Wed Oct 26, 2011 10:44 pm

    Baddog,
    I like the Aluminum chassis design it is a logical update to the original. Big improvement. Is someone in the States cutting the aluminum? If so I would like to buy one if yours turns out to be the quality ordered. Please post that information.
    JDM

    baddog1946

    Posts : 304
    Join date : 2010-02-03
    Location : Costa Rica

    Re: My new ST-120A custom amp chassis

    Post by baddog1946 on Wed Oct 26, 2011 11:18 pm

    I will keep you posted and try to photo document the build on this forum.
    The chassis is being made by "Front Panel Express". I should have it by the first of November.
    How long it will take will depend on getting all the parts from Bob to me as I live in Costa Rica. I am pulling the $$ together for that right now. Stay tuned.

    Sponsored content

    Re: My new ST-120A custom amp chassis

    Post by Sponsored content Today at 3:05 pm


      Current date/time is Sun Sep 25, 2016 3:05 pm