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    Dynaco lore - Differences between factory wired and kit built ST-70 - photos ..

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    Bob Latino
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    Posts: 1957
    Join date: 2008-11-26
    Location: Massachusetts

    Dynaco lore - Differences between factory wired and kit built ST-70 - photos ..

    Post by Bob Latino on Fri Dec 26, 2008 7:01 am

    Dynaco offered the ST-70 in both kit and factory wired versions. Although over 350,000 ST-70's were sold during the run of this amp, it is estimated that less than 5% of all ST-70's were factory wired units. Only a few ever show up for sale on Ebay. Are there any differences between the kit built units and those that were factory wired ? Although the circuit is the same there were some cosmetic and at least one one wiring difference ...

    Bob

    1. The wired ST-70 was called the "70-A" (A = assembled) and came with a different user manual. This 6 inch by 9 inch manual was smaller in size than the standard 8 1/2 by 11 inch manual that came with all kit amps.


    2. The 70-A had its chassis components attached with rivets instead of 4-40 pan head screws. The exceptions were the front stereo/mono switch and the power switch on the rear of the amp. Reason - those two switches were threaded and the rivets wouldn't pass through the threaded hole.


    3. The driver board on the ST-70-A had its own separate "driver board cage"


    4. The rear of the amp had a small "factory assembled" tag.


    5. The chassis had a factory installed "spanner screw" to discourage the user from removing the bottom cover. You could remove the tube cage for bias adjustments because the cage had a slot that slid over the spanner screw but in order to remove the bottom cover and get at the internal wiring you needed a spanner wrench.


    6. On KIT ST-70's the assembly manual tells you to install a 1000 ohm resistor between pins 5 and 6 of each output tube. Pin 6 is not used on an EL34 and is just used as a tie off point for one side of the resistor. On the factory wired units the 1000 ohm resistor goes directly from pin 5 to the driver board and there is no connection for pin 6

    Clik2media

    Posts: 40
    Join date: 2009-01-18

    Re: Dynaco lore - Differences between factory wired and kit built ST-70 - photos ..

    Post by Clik2media on Tue Jan 20, 2009 7:08 pm

    Would you say "factory wired" are more in demand [now-a-days], than "kit" wired.... just a thought. Very Happy

    Bob Latino
    Admin

    Posts: 1957
    Join date: 2008-11-26
    Location: Massachusetts

    Re: Dynaco lore - Differences between factory wired and kit built ST-70 - photos ..

    Post by Bob Latino on Tue Jan 20, 2009 7:18 pm

    Clik2media wrote:Would you say "factory wired" are more in demand [now-a-days], than "kit" wired.... just a thought. Very Happy

    If you are a "collector" of Dynaco tube gear then the factory wired version is more "collectable" and therefore worth more. From the standpoint of sound quality the sound is the same from either the kit or the factory wired unit.

    Bob

    vav2sab

    Posts: 6
    Join date: 2010-09-08

    Re: Dynaco lore - Differences between factory wired and kit built ST-70 - photos ..

    Post by vav2sab on Thu Sep 16, 2010 1:01 am

    Hi Bob,

    I have seen some ST-70 (mainly on eBay) claimed as "factory-wired", but, according to your post, they are "kit-wired" for sure. Here's one example (already sold as "factory-wired"): http://cgi.ebay.de/Factory-Original-1962-Dynaco-Dynakit-ST70-ST-70-Stereo-/160472356592?pt=Vintage_Electronics_R2&hash=item255ce5d6f0.

    Even after the inquiry with the reference to this forum topic, the seller has answered:

    "There is no doubt in my mind that this was factory built in 1962- three to four years before the one shown on the site.
    Regards,
    Radioorphanage"

    Could it be that DYNA used other wiring techniques at the beginning?

    I bought mine ST-70 as a "kit-build", although it carries a "factory-wired" label similar to the one shown in one of the photos of the referred eBay article. Bias pots are dated 1964.

    Vytas

    Bob Latino
    Admin

    Posts: 1957
    Join date: 2008-11-26
    Location: Massachusetts

    Re: Dynaco lore - Differences between factory wired and kit built ST-70 - photos ..

    Post by Bob Latino on Thu Sep 16, 2010 6:43 am

    Hi Vytas,

    The usual yardstick for checking out whether an ST-70 was factory wired was whether RIVETS were used to attach most of the components on the amp. Also, that the amp had a cage over the driver board and a "factory wired" sticker. That amp at the Ebay link has the factory wired sticker but no rivets or driver board cage. It is possible that because this amp was an earlier ST-70 that it is truly a wired ST-70. I don't think anyone would go through the bother of having a wired amp sticker made up just to sell the amp for a little more money. My opinion - It probably is an earlier wired ST-70.

    Bob

    vav2sab

    Posts: 6
    Join date: 2010-09-08

    Re: Dynaco lore - Differences between factory wired and kit built ST-70 - photos ..

    Post by vav2sab on Fri Sep 17, 2010 3:12 am

    I am starting to believe, mine ST-70 is factory-wired as well (as I wrote before, the pots are dated 1964). Does anybody know, if this could be tracked via the serial number?

    GP49

    Posts: 499
    Join date: 2009-04-30

    Re: Dynaco lore - Differences between factory wired and kit built ST-70 - photos ..

    Post by GP49 on Fri Sep 17, 2010 9:41 am

    vav2sab wrote:I am starting to believe, mine ST-70 is factory-wired as well (as I wrote before, the pots are dated 1964). Does anybody know, if this could be tracked via the serial number?

    Not since the real, original Dynaco company shut down. They maintained them and continued to have them for reference after they moved from Philadelphia across the river to New Jersey; they could look up any serial number you wanted but as far as I know, those files went to a landfill after Tyco closed the factory. Panor didn't get anything but the name, trademarks and the rights to the designs, most of which they promptly threw away.

    Valvebloke

    Posts: 4
    Join date: 2010-09-19
    Location: Southern England

    Re: Dynaco lore - Differences between factory wired and kit built ST-70 - photos ..

    Post by Valvebloke on Sun Sep 19, 2010 11:37 am

    Hi Everyone,

    I'm new here, and from England, so apologies if my language is sometimes incomprehensible. I'll do my best to remember "tube" and "wrench" and the fact that the metric system may not be everyone's first choice Smile.

    I'm also new to Dynaco, as of yesterday, when I finally got hold of an ST-70. Sadly they're not so common over here, so I've had to wait a while, nor are they as cheap as in the US I'm afraid. But now I have one, and having made up some speaker leads I spent the rest of yesterday listening to it. It's a peach ! So now I'm ready to see what I can find out about it.

    It seems to be factory wired. At least, it's got the rivets and the label. But it doesn't have the "spanner screw" - in fact it's only got two screws each side. And the 1k grid-stopper resistors are wired onto the tube bases, not direct to the PC board. I can't see any sign of a factory inspection stamp either. Strangest of all is that the PC board appears to be contemporary with the rest of the amp, but it is green (fiber glass ?) with the legend STEREO PC3 in one corner. Was this kind of board ever used by Dynaco or is it a more recent replacement ? And is the general opinion that this really is a factory wired amp ?

    I'd also be interested to know what date it is. The electrolytic capacitors are no help - they've been renewed. The serial number is 6410912. I read in another thread that Dynaco's serial number records no longer exist. But maybe there are forum members who know both the date and the serial number of their amps and who might at least set some limits on which ones were made when ? I also read that the bias pots can be dated. I can't see anything which looks obviously like a date on mine. But they have the numbers 1376402, and EQ9373 stamped into the underside as well as the 10k resistance value. Is the date in there somewhere ?

    In general I think the amp is in quite good condition. There are some blemishes (scratches, small rust spots etc in the chrome, a few scrapes on the cage paint, some lettering missing). But it's probably not much younger than I am and I'm not scratch-free either ... If I could change one thing I would quieten the mains transformer. It buzzes significantly and the cage and chassis seem to resonate and amplify this. Of course the AC supply runs at 50Hz here so it may be that I will see different problems from the ones you're used to. I think I will try the anti-vibration isolators first. They're not expensive and I can take them out again if they don't work. I have to say I'm tempted by a replacement transformer. This should both fix the hum and also let me wire the primaries for 240V which would mean I could dispense with the step-down transformer I'm currently using. On the other hand a new transformer won't be cheap (I've got transatlantic shipping as well as import duty on top of the base price). And some part of me really doesn't want to mess with what might be a fairly untouched unit. So I think I'll wait a while and see what the isolators do.

    OK, enough for now. I've attached a few pictures to show what I've been talking about.

    All the best,

    Valvebloke







    Greg_M

    Posts: 40
    Join date: 2010-09-18
    Location: Poulsbo, WA

    Re: Dynaco lore - Differences between factory wired and kit built ST-70 - photos ..

    Post by Greg_M on Mon Sep 20, 2010 8:29 pm

    Is it possible to get a larger size version of the "Factory Wired" interior picture.

    It would help a lot in tracking wires down and finding potential screw ups.

    Thanks

    Valvebloke

    Posts: 4
    Join date: 2010-09-19
    Location: Southern England

    Re: Dynaco lore - Differences between factory wired and kit built ST-70 - photos ..

    Post by Valvebloke on Tue Sep 21, 2010 2:08 am

    My digital camera is not new, so the resolution is not up to the best modern standards, but it still produces original pictures with about ten times as many pixels as the reduced-sized version which the forum software enforces (we're limited to 800x600 on the forum whereas my originals are 2560x1920). There isn't a great deal more detail in these than in the ones posted here but if you think they might be useful then I'll happily send them to you. I don't have them hosted anywhere on the web but if you want to PM me your e-mail address I'll copy them to you directly. Just let me know which ones you want. I also have a similar-sized interior shot taken with a flash. Overall I think it is less good than the one shown above, but it may show some details better.

    All the best,

    Valvebloke

    vav2sab

    Posts: 6
    Join date: 2010-09-08

    Re: Dynaco lore - Differences between factory wired and kit built ST-70 - photos ..

    Post by vav2sab on Tue Sep 21, 2010 5:06 am

    Hi Valvebloke,

    You should have read the post about the bias pots more thoroughly - the number 1376402, means the pots are dated week 2 of the year 1964 (137 is a kind of item ID which is likely to be common for all original ST-70 bias pots). The age of your ST-70 is similar to mine's, but mine has no rivets although has the label with the serial. I'm confused again now, while I was starting to think, mine was factory-wired too (see previous posts in this topic). Nevertheless, everything seemed untouched when I bought it two weeks ago, and I think the overall condition was excellent - no rust or noticeable scratches.
    Your driver bord is definitely some later replacement, while the original should be the brown (phenol?) one. I have only replaced selenium rectifier with a diode so far - awaiting for the bias caps and paper-oil driver caps. I have experienced no hum or any other noise from the amp, just right channel makes som "scratching" noise during the warm-up phase.

    Greg_M

    Posts: 40
    Join date: 2010-09-18
    Location: Poulsbo, WA

    Re: Dynaco lore - Differences between factory wired and kit built ST-70 - photos ..

    Post by Greg_M on Tue Sep 21, 2010 7:08 am

    Valvebloke wrote:My digital camera is not new, so the resolution is not up to the best modern standards, but it still produces original pictures with about ten times as many pixels as the reduced-sized version which the forum software enforces (we're limited to 800x600 on the forum whereas my originals are 2560x1920). There isn't a great deal more detail in these than in the ones posted here but if you think they might be useful then I'll happily send them to you. I don't have them hosted anywhere on the web but if you want to PM me your e-mail address I'll copy them to you directly. Just let me know which ones you want. I also have a similar-sized interior shot taken with a flash. Overall I think it is less good than the one shown above, but it may show some details better.

    All the best,

    Valvebloke


    I have PMed you my email address


    What I'm mostly interested in is a photo of the interior of the ST70. The different colored wires used by the factory makes it easier to zoom in and look and see where the wires should be going. Whoever wired mine was not very "clean" in his techniques.

    Having a high resolution photo will make it easier to zoom in on an area and see how it is supposed to look.

    Thank you for you time and effort

    Greg

    Valvebloke

    Posts: 4
    Join date: 2010-09-19
    Location: Southern England

    Re: Dynaco lore - Differences between factory wired and kit built ST-70 - photos ..

    Post by Valvebloke on Tue Sep 21, 2010 8:54 am

    vav2sab wrote:You should have read the post about the bias pots more thoroughly.

    The post I read was yours - #4 in this thread. I don't think it contains an explanation of the code, but thanks for explaining it here.

    vav2sab wrote:The age of your ST-70 is similar to mine's.

    Well, strictly speaking the age of the bias pots is. I guess, in principle at least, Dynaco could have bought a large quantity and used the stock over a number of years. Or they could have made repeated purchases from a wholesaler who kept a large stock of the '64 production. But at least we know our amps are not from before '64 which, for me at least, is real progress Smile .

    vav2sab wrote:Your driver bord is definitely some later replacement, while the original should be the brown (phenol?) one.

    Actually since my original post I read in this thread http://dynacotubeaudio.forumotion.com/basket-f2/dynaco-st-70-pc-3-driver-board-parts-layout-photo-t191.htm that Dynaco supplied fiberglass boards with their later ST-70s. The one that Bob Latino shows looks a little different from mine, but he seems convinced it's original (and not phenolic). However if you're sure that he and vleena (post #16) are wrong then that's very interesting. In any case there's some incompatibility between my fiberglass board (late production ?) and my '64 pots. Hmmm ...

    Valvebloke

    vav2sab

    Posts: 6
    Join date: 2010-09-08

    Re: Dynaco lore - Differences between factory wired and kit built ST-70 - photos ..

    Post by vav2sab on Tue Sep 21, 2010 9:51 am

    I am sorry - I was (and I thought you were too) referring to this post

    http://dynacotubeaudio.forumotion.com/basket-f2/st-70-mark-ii-mark-iii-and-mark-iv-to-check-your-date-of-manufacture-t105.htm#390

    Now we have some new facts which influence the mentioned post about the age of some Dynaco devices. On one hand Bob wrote, the pots used to come and go at Dynaco's, but on the other hand your ST-70 (rivets, some components and newer driver board) suggests that they probably kept larger stocks of some components.
    However, your ST-70 has a rectifier diode instead of the original selenium rectifier, bias caps seem to be relatively new, and the quad cap shape is different from the original (lower and thicker). Did those components come with later batches, or the unit has already been repaired or modified - I cannot say. There are much more experienced members of this forum who may have noiticed more significant details.

    Vytas

    Valvebloke

    Posts: 4
    Join date: 2010-09-19
    Location: Southern England

    Re: Dynaco lore - Differences between factory wired and kit built ST-70 - photos ..

    Post by Valvebloke on Tue Sep 21, 2010 10:28 am

    No problem Vytas, and thanks for the link to the pot date thread. I am pretty sure that the Quad cap and the two electrolytics on the tag strip have been replaced very recently. I am not so sure about the diode which is where the selenium rectifier would have been, but I suspect that that is recent too. As far as the board is concerned, I think the Dayton capacitors are in fact current production http://www.daytonaudio.com/loudspeaker/capacitors.html ! However when I look really closely I can see traces of solder flux around the pads that these are connected to. There seems to be no flux around the other pads, so perhaps the new Dayton capacitors have been put into an older board ? I don't know how much older though. The 82pF Erie capacitors look identical to the ones shown in Bob's picture of his fiberglass board.

    Valvebloke

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