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    Best way to clean ST70 Chassis? Best replacement components?

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    heyraz

    Posts : 58
    Join date : 2011-10-26

    Best way to clean ST70 Chassis? Best replacement components?

    Post by heyraz on Mon Oct 31, 2011 4:47 pm

    The ST70 I recently got from an estate sale was assembled by a hack. Never saw anything like it, no wonder it hummed. Therefore, I've decided to pull everything out, clean the chassis up, use a VTA driver board, replace everything else and put things back in there nice and neat.
    I have a few questions:
    1- What's the best way to clean the grime etc from the chassis without ruining the lettering? I used a little rubbing alcohol that removed most of the dirt, but I'm wondering if anyone has another tried and true method.
    2- Once the transformers are off, wouldn't it be a good idea to put rubber grommets in the holes where their wires pass through? I can't think of a reason not to other than cost, unless they can't stand the heat or get in the way of something else.
    3- Since this is actually a "new build" using the old chassis and transformers, is there an assembly manual rather than an upgrade manual available (as though I was building a new VTA Amp)? I'm sure I can figure things out for myself, but I like to check things off once and a while. For example, I think the heater wires should be solid and color coded to ensure proper phase, what gauge is recommended? Should I look for a high temperature wire, perhaps THHN or Thermostat wire?
    4- The original choke has leaked all over the place, is there a preferred replacement brand/value?
    5- Any recommendations with regard to resistor types and where they go? Carbon comp, metal oxide, NOS?
    6- New tube sockets-I plan on keeping them black. I've read that a tube socket should be regarded as an important component. I see there are different contact types, gold plated round, cadmium plated finger contacts, what's recommended? Any preferred brands? The original sockets were loose fitting, which I think contributed to ruining a tube and resistor. I'd like to prevent any future problems. I'm not too concerned about cost, but I don't want to waste money either.
    Thanks in advance... Rich

    tubes4hifi
    Admin

    Posts : 1261
    Join date : 2008-11-30

    Re: Best way to clean ST70 Chassis? Best replacement components?

    Post by tubes4hifi on Mon Oct 31, 2011 9:11 pm

    Hi Rich,
    you can download the ST70 assembly manual here: www.tubes4hifi.com/DynaST70.pdf
    you may want to consider getting a complete new kit, less the chassis and transformers.
    Either Bob at Tubes4HiFi.com or Kevin at DynaKitParts.com can help you with that.
    Kevin also has new chokes and grommets (as does the complete kit Bob sells).
    I'm sure someone will recommend some industrial metal cleaner, but for what's around the house,
    I've used 409 cleaner/degreaser, and the green scruff pad on a kitchen sponge.
    The lettering on the chassis won't come off unless you actually try very hard to scrub it off.

    j beede

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

    Re: Best way to clean ST70 Chassis? Best replacement components?

    Post by j beede on Tue Nov 01, 2011 1:50 am

    Hum is typically an idicator that the quad cap has bad segments. Are you trying to clean or polish the chassis? Flitz has worked pretty well for me--the chassis will never look like chrome though. ST-70 assembly manual is available on this site. Have you done listening tests with heater phase changes? What did you learn? Is the choke humming? If not, clean up the goo and reuse it.

    heyraz

    Posts : 58
    Join date : 2011-10-26

    Re: Best way to clean ST70 Chassis? Best replacement components?

    Post by heyraz on Tue Nov 01, 2011 2:30 am

    I briefly ran the ST70 right after I got it. It was obvious from the hum and it's general condition that it would need some work. As I tried to measure and adjust the bias I smelled smoke and saw a tube start to run away, but I couldn't unplug it fast enough. When I opened the bottom I found a blown bias resistor and was disgusted by the shoddy workmanship, that's why I decided to rip everything out and start fresh.
    Phasing the heaters is just something I think should be done, I mean why not? I'll need different colored wires to do that, which is why I'm wondering what's the preferred gauge and insulation. Regarding the choke, it just doesn't make sense to reuse it, so I'll change that too. And the sockets, they were very loose, while I'm at it, I'll replace them too.
    Concerning the assembly manual, I have the original but it pertains to the 7199 board. The VTA upgrade instructions has me removing things from the original design (for example-no mono switch). I was looking for an assembly manual for a new amp based on the VTA board. No big deal though, I can figure it out, I just like to keep good records for the future when I build things.
    Thanks for responding. Rich

    stewdan

    Posts : 160
    Join date : 2010-03-07
    Age : 78
    Location : Houston Texas

    ST120/VTA Assembly Manual

    Post by stewdan on Tue Nov 01, 2011 8:42 am

    Hi -- There is an partial assembly type manual on the Tubes4HiFi Website for the ST120/VTA which is a "ST70 with 60 watts per channel plus the VTA Board". It is not exactly what you have, but might be helpful and what you are looking for.

    Go to http://www.tubes4hifi.com/bob.htm and scan down the page until you see the link for the partial manual at --

    www.tubes4hifi.com/ST-120_sample_manual.pdf

    Another user also posted a link on Bob's page with pictures of his build of a ST70/VTA amp.

    Have fun!!



    j4570

    Posts : 141
    Join date : 2010-08-30

    Re: Best way to clean ST70 Chassis? Best replacement components?

    Post by j4570 on Tue Nov 01, 2011 11:15 am

    Take a look at my rebuild, I only used the chassis and output trannies from the original (the power tranny had rotted wires, so I got a new one as a precaution). I got everything else new from Bob. I could have almost went new for the price (probably saved $100 or so, as I did pay something for the used amp). But I have all the upgrades, caps, Russian PIO, attenuator, etc. I used a variety of cleaners like Windex, and some Flitz as mentioned in some really cruddy areas. Bob included complete step by step build instructions. Here's a pic to my build thread, read the whole thread as I made some comments too (on wire, etc):

    http://dynacotubeaudio.forumotion.com/t804-my-st70-rebuild-progress

    Here is the built VTA board:

    http://dynacotubeaudio.forumotion.com/t790-pics-of-my-vta-st70-driver-board-build

    I love my amp.

    kaner

    Posts : 88
    Join date : 2011-09-20

    Cleaning the chassis

    Post by kaner on Wed Nov 02, 2011 10:15 pm

    I know this may sound a bit scary but I used 0000 steel wool and it really worked well to clean the chassis. Try it on the inside first if you're skeptical. It won't scratch the finish and it takes off rust and other grime.

    GP49

    Posts : 717
    Join date : 2009-04-30
    Location : East of the sun and west of the moon

    Re: Best way to clean ST70 Chassis? Best replacement components?

    Post by GP49 on Thu Nov 03, 2011 10:21 am

    kaner wrote:I know this may sound a bit scary but I used 0000 steel wool and it really worked well to clean the chassis. Try it on the inside first if you're skeptical. It won't scratch the finish and it takes off rust and other grime.

    What's the plating on the stock Stereo 70 chassis? Is it hard chrome, like car bumpers before they became plastic? 0000 steel wool is a cleaning method that's been used on hard chrome for ages.

    tubes4hifi
    Admin

    Posts : 1261
    Join date : 2008-11-30

    Re: Best way to clean ST70 Chassis? Best replacement components?

    Post by tubes4hifi on Thu Nov 03, 2011 2:01 pm

    the old original Dynaco ST70s used a hard nickel chrome on steel chassis, just like bumpers on cars from the 50s and 60s.

    heyraz

    Posts : 58
    Join date : 2011-10-26

    Re: Best way to clean ST70 Chassis? Best replacement components?

    Post by heyraz on Thu Nov 03, 2011 4:50 pm

    Mine is an old original, cloth insulation on the trannys. I'll try some chrome cleaner and let you know.

    j4570

    Posts : 141
    Join date : 2010-08-30

    Re: Best way to clean ST70 Chassis? Best replacement components?

    Post by j4570 on Thu Nov 03, 2011 8:49 pm

    Chrome cleaner is very similiar to Flitz. Matter of fact, I threw out a little bit of dried up Car Bumper Chrome cleaner last month. Probably 15 years old. I probably could have added water, but it wasn't worth it.

    When we had chrome bumpers, I used steel wool as a last resort! But always 0000. No point buying a mix pack that Wally World or some others sell, you'll probably never have a use for the coarse stuff.

    Steel wool still works better for stuff like this than scotchbrite pads (even if you get the fine ones). I was taught to use WD-40 and steel wool. The WD-40 is not only a little lubrication, it's a great solvent to erase the crud. WD-40 removes stickers, etc off file cabinets quite well, with a real cotton rag, and some elbow grease.

    Jason

    Luddite

    Posts : 235
    Join date : 2009-02-04
    Age : 66
    Location : Texas

    Re: Best way to clean ST70 Chassis? Best replacement components?

    Post by Luddite on Thu Nov 03, 2011 9:37 pm

    I've mentioned this before in an earlier post, but after you get the chassis cleaned up, I would recommend a silicone impregnated gun cloth for occasional polishing. It helps remove and reduce fingerprints. These should be readily available from your local gun or sporting goods store.

    Best Regards,
    Charlie

    heyraz

    Posts : 58
    Join date : 2011-10-26

    Re: Best way to clean ST70 Chassis? Best replacement components?

    Post by heyraz on Thu Nov 03, 2011 10:00 pm

    Thanks for the suggestions. Now that I know what it's made of (nickel chrome on steel), I'll speak to some auto restoration buddies of mine.

    sailor

    Posts : 269
    Join date : 2011-04-04

    Re: Best way to clean ST70 Chassis? Best replacement components?

    Post by sailor on Fri Nov 04, 2011 5:50 pm

    Flitz liquid polish is the way to go. It uses chemicals in stead of abrasives to clean and polish. You can make ordinary metal shine better than new. I used it on some of my Dynaco gear with great results, except really bad rust and super pitted dynaco 70's. Can you say sand paper and primer time. I also use it on my sailboat to clean all of the different types of metal. Its great stuff. You just put a little on and polish until no more black residue shows up on the rag.

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