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The Dynaco Tube Audio Forum

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


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    ST-70 CHASSIS

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    moodyj2000


    Posts : 12
    Join date : 2023-01-18

    ST-70 CHASSIS Empty ST-70 CHASSIS

    Post by moodyj2000 Wed Jan 18, 2023 6:25 pm

    I have  been reading on this forum for a while but just recently decided to join.  Great information!

    I recently purchased some Dynaco parts from a gentlemen and it had two sets of ST-70 transformers and chassis.  I am working on putting one set back together currently and noticed something interesting about the chassis.  In the location of what should be the mounting point for the twist lock can capacitor there is just another tube socket.  Everything else is stock.  I ordered a 1-3/8" can capacitor clamp that I am planning on just installing at that point to hold it in place.  Anyone else ever seen this?  Was there some other intent for this location?

    Also, neither chasis in the lot had any markings.  One is chromed and the other is stainless steel.  The stainless steel one I am thinking about getting a black oxide treatment on but the chrome one is what I am working on now.

    Thanks in advance for any advice on that can capacitor issue.

    Jason
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    moodyj2000


    Posts : 12
    Join date : 2023-01-18

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    Post by moodyj2000 Wed Jan 18, 2023 6:35 pm

    ST-70 CHASSIS 2023-010
    peterh
    peterh


    Posts : 1718
    Join date : 2012-12-25
    Location : gothenburg, sweden

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    Post by peterh Wed Jan 18, 2023 7:33 pm

    By altering the cap mounting slots you will have some trouble mounting a dynacp-type cap.

    You could junk this and get a new ( stainless less vibrant) chassies at dynakitparts.com that has
    all the lettering.
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    stewdan


    Posts : 227
    Join date : 2010-03-07
    Age : 84
    Location : Houston Texas

    ST-70 CHASSIS Empty St-70 Chrome Chassis

    Post by stewdan Thu Jan 19, 2023 12:18 am

    Moody --- over the last 50 years or so all sorts of mods have been done to the original ST-70.  

    One mod was to add a 2nd Rectifier tube in parallel to the original GZ34.   They would re-cut the hole for the Quad Cap and mount the 2nd GZ34 in its place. This was done so they could use a power tube that required more current than a single GZ34 could provide, like the 8417 tube which is no longer manufactured or available.

    The quad cap would then be mounted underneath the chassis (space permitting) or individual caps making up 30-20-20-20 or they would mount a capacitance board in the space under one of the output transformers.

    See Triode USA Electronics .....  http://www.triodeelectronics.com --- under Dynaco AMPS and Kits for their cap board for the ST-70 to see what I explained.

    Here is their description ----
    Triode Electronics ST70 Capacitor Board:This Power Supply board replaces the original can capacitor in Dynaco ST70. (You can leave the old one there for looks if you like) Bolt on standoffs under the output transformer, no cutting or drilling required to install, just bolt in, hook up the wires and go! NEWLY DESIGNED! Upgrade Cap Board: New Updated Version!!! This is a new, updated, version of the classic, SDS Labs, ST-70 Capacitor board. We have upped the capacitance to over 500uF @ 500V (Increases capacitance from original 30-20-20-20 to 40-195-135-135) while at the same time shrinking the board to make it fit into the chassis more comfortably. The board still replaces all bias supply components and we have also added 0.1uF Wima MKP series metallized polypropylene bypass capacitors onto the board. There are no more surface mount resistors as used on the old boards, instead we have standard axial metal film resistors that are easy to mount and solder in place. There is also a cutout on the back of the board to make clearance for using binding posts in the amplifier rather than the original screw terminal strips. The board is a high quality .062 FR4 2oz Copper with plated through holes which allow you to solder/resolder connections with the board already mounted in place. Now with clearer and more detailed instructions.
    (Note that the maximum capacitor size is 25mm long by 30mm diameter, board requires 8 pieces rated 250V or more)
    Board with instructions, all capacitors, parts & amp; hardware.

    I dont use a Quad Cap on my St-70, but I use one of the Triode Cap Boards.

    Hope I answered your question about the Quad-Tube Socket issue.  If you need any more info, just ask.
    Stew

    10-E-C and moodyj2000 like this post

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    moodyj2000


    Posts : 12
    Join date : 2023-01-18

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    Post by moodyj2000 Thu Jan 19, 2023 1:41 pm

    Stew,

    Thanks for the information. I have actually seen a 70 modded like you mentioned. At the time I just didn't know that much about them and it make since. I have a cap holder in route that I will see if it will work. If not then I will mount a dummy socket in this spot and put a matching 5AR4 in it. I have one that is new but damaged on the inside and was about to throw it away.

    As part of this lot there was another stainless steel chassis with brand new power and output transformers along with a VTA Octal board. That one I am going to order the capacitor board for. It is one of Triode Electronics chasis anyway and it doesn't have a hole for a can cap.

    Jason
    baddog1946
    baddog1946


    Posts : 320
    Join date : 2010-02-03
    Location : Costa Rica

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    Post by baddog1946 Tue Jan 24, 2023 2:16 pm

    The other anomaly of that chassis is the power transformer cut out is different than normal. Is this some heretofore unknown mfr, or a stock Dynaco variation?
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    moodyj2000


    Posts : 12
    Join date : 2023-01-18

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    Post by moodyj2000 Tue Jan 24, 2023 2:22 pm

    That board is a definite anomaly. It was apparently a pitted chassis that someone chrome plated. While cleaning off some of the dirt the chrome plating started to peel at a few points. I ordered a new chassis from dynakit.com. I will probably have a friend powder coat this on and either save it for a project chassis or sell it.
    peterh
    peterh


    Posts : 1718
    Join date : 2012-12-25
    Location : gothenburg, sweden

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    Post by peterh Tue Jan 24, 2023 2:24 pm

    baddog1946 wrote:The other anomaly of that chassis is the power transformer cut out is different than normal. Is this some heretofore unknown mfr, or a stock Dynaco variation?
    It seems that the previous owner has been active. Maybe cutting for another mains transformer ?

    ( this is shown on picture in post #2 )

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