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    Dynaco SCA35

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    Peter W.
    Peter W.

    Posts : 1168
    Join date : 2016-08-07
    Location : Melrose Park, PA

    Dynaco SCA35

    Post by Peter W. on Wed Jan 23, 2019 11:21 am

    https://www.ebay.com/itm/Dynaco-Dyna-SCA-35-Stereo-Tube-Amplifier-Factory-Wired-SUPER-COOL/303032107484?hash=item468e1f01dc:g:wvoAAOSwGYhcGAQ2:rk:3🇵🇫1&frcectupt=true

    Note the red-plating 6BQ5 about photo #4.

    I have a rather low snipe set for this beast, and over the years, I have accumulated all the various parts-and-pieces as it might need for repair, including boards, transformers and so forth. But, if anyone wishes to save me from myself, you are most welcome...

    Should I get it, I do enjoy the challenge! And when restored, I would most likely recycle it to one of the grandkids. The oldest has my Revox system, the next in line has expressed an interest in tubes, and the SCA35 is a very nearly perfect (as in kid, pet and bulletproof) option.
    WLT
    WLT

    Posts : 86
    Join date : 2013-07-13
    Location : Rochester NY

    Re: Dynaco SCA35

    Post by WLT on Wed Jan 23, 2019 12:42 pm

    I will not save you. Hope you get it

    I just finished rebuilding one for a guy. All new caps on both board and in the power supply. The 95 ohm cathode resistor tested fine but when I inspected the bottom of it I found a very dark area and a crack running thru it. An important resistor that was close to the end of its life. I have a supply of 10 W 100 ohm wire wound resistors that works out great for these. Slightly higher resistance yields slightly lower output tube idle current and the 10 watt rating runs much cooler. Also enough room under their to mount without bumping into other stuff.
    peterh
    peterh

    Posts : 1107
    Join date : 2012-12-25
    Location : gothenburg, sweden

    Re: Dynaco SCA35

    Post by peterh on Wed Jan 23, 2019 1:12 pm

    Gillespies EFB board fits very well for these, and you don't have to search for new can-caps.
    Peter W.
    Peter W.

    Posts : 1168
    Join date : 2016-08-07
    Location : Melrose Park, PA

    Re: Dynaco SCA35

    Post by Peter W. on Wed Jan 23, 2019 1:31 pm

    peterh wrote:Gillespies EFB board fits very well for these, and you don't have to search for new can-caps.

    Thank you!

    I would not use new can-caps in any case. I would either install the separate board, or restuff the cans. I have a plumbing tubing cutter that does an excellent and very clean job of cutting the cans right where it is needed. Ridgid, of course.
    Peter W.
    Peter W.

    Posts : 1168
    Join date : 2016-08-07
    Location : Melrose Park, PA

    Re: Dynaco SCA35

    Post by Peter W. on Wed Jan 23, 2019 7:18 pm

    Got it. OK with the price, shipping is a little rich, but such is life. I will post pictures of the process.
    Peter W.
    Peter W.

    Posts : 1168
    Join date : 2016-08-07
    Location : Melrose Park, PA

    Re: Dynaco SCA35

    Post by Peter W. on Wed Jan 30, 2019 8:46 am

    It arrived last night (9:00 pm via FedEx). Upon brief examination, it is 'all there' but for the two missing knobs - I have plenty of those. I will take a range of 'before' pictures on Saturday and post a link.
    Peter W.
    Peter W.

    Posts : 1168
    Join date : 2016-08-07
    Location : Melrose Park, PA

    Re: Dynaco SCA35

    Post by Peter W. on Mon Feb 04, 2019 8:35 am

    https://www.dropbox.com/sh/byzusvy367c3cfc/AAAp2A5qpD0Y1FfSogHk-xWIa?dl=0  

    a) Bent sheet-metal - the fencing pliers took care of that.
    b) Frozen controls - why izzit that individuals insist on using so-called 'lubricants' off-label. In this case, lithium grease that has turned to lithium concrete. The controls are soaking in Kroil as I type.
    c) Just plain filthy - as the pictures will show. The bass control may be unsalvageable. I do have spares.
    d) A mix of German (OEM Dynaco 12AX7s x 2), Japanese (3 x Raytheon 6BQ5) and US (RCA 7199 x 2, Zenith 6BQ5 x 1). They all test OK on the big Hickok.
    e) Draws about 95 watts @ 118 VAC unloaded. Nameplate is 110 watts. After I clean it up and check the caps that may calm down a bit.
    f) 5A standard fuse. Ouch!

    Gonna be a challenge.
    Gonna be fun.
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    nmchiefsfan

    Posts : 48
    Join date : 2012-03-21

    Re: Dynaco SCA35

    Post by nmchiefsfan on Mon Feb 04, 2019 11:43 am

    Looks like fun! Enjoy!!
    WLT
    WLT

    Posts : 86
    Join date : 2013-07-13
    Location : Rochester NY

    Re: Dynaco SCA35

    Post by WLT on Mon Feb 04, 2019 4:23 pm

    Did the straightening of the sheet metal leave a crease? It looks nice and true in the photos.

    I see there are new circuit boards for both the phono and audio sections available on Ebay. They are from China but they do not look bad. Made from FR4 with thru plating of the holes in what looks like the correct locations. I have not tried any but wondered if you or others have?
    Peter W.
    Peter W.

    Posts : 1168
    Join date : 2016-08-07
    Location : Melrose Park, PA

    Re: Dynaco SCA35

    Post by Peter W. on Mon Feb 04, 2019 4:37 pm

    WLT wrote:Did the straightening of the sheet metal leave a crease? It looks nice and true in the photos.

    I see there are new circuit boards for both the phono and audio sections available on Ebay. They are from China but they do not look bad. Made from FR4 with thru plating of the holes in what looks like the correct locations. I have not tried any but wondered if you or others have?

    I spend several years of my mis-spent youth as a machinist, and worked my way through school as an electrician. During that time, I learned a few very basic skills with sheet metal. No creases, and no visible marks. Fencing pliers allow me to reach around flanges so that I can grip the flats. Handy to avoid creasing (crimping).

    I have a set of Chinese boards - as you suggest, they do not look bad, and after a few re-solders, they are actually pretty good. What will happen is that after the basic diagnosis, cleaning and electrical checks, I will either install the new boards or rebuild what is there. Either way, the incumbent boards will be rebuilt for 'the next one'. The Chinese boards came out of a donor SCA - that, somehow, had blown the power transformer and one of the output transformers. Go figure. But that will be the source of spare controls and such, if needed.
    Peter W.
    Peter W.

    Posts : 1168
    Join date : 2016-08-07
    Location : Melrose Park, PA

    Re: Dynaco SCA35

    Post by Peter W. on Sun Feb 10, 2019 6:17 pm

    Update: Pictures tomorrow.

    After washing the beast down in WD-40 into a trash-can properly lined with kitty-litter I could see actual components on the boards beneath the sludge and scum - as seen previously. Then a rinse in CRC Electrical solvent to get the last of the hardened lithium grease from the controls and where it had melted all over the bottom of the chassis. . I freed the frozen controls completely, but for the selector switch, using a combination of Liquid Wrench and Kroil. The selector switch is undergoing its "second Kroil" immersion, as I type.

    Previously, I had checked all the connections, cleaned the tube sockets and tested the tubes. I applied power without the tubes and got a rock-steady 20 watts, with no discernible heat at the caps or transformers. 20 watts over all that is not-much, so I was not at all surprised that after an hour, I should be getting no significant heat signatures.

    Meanwhile, the selector worked free enough for me to set it on the "Spare" position.

    More cleaning with a stiff artist's brush and high-proof alcohol. Soaked the knobs in hot ammonia with dish soap, then a tooth brush. More can be done, but I will have to raid my wife's Cream-of-Tartar for that work. Replaced all four feet, did a very brief plate-current match of the output tubes, replaced the tubes and fired up the amp unconnected to anything, spare input shorted. Went to about 80 watts quiescent, rock steady for an hour, no more heat than one might expect anywhere.

    Let it rest for 20 minutes. Added speakers and a signal (Dynaco AF6 tuner) - and Thar She Blows - music! Not a trace of hum, buzz or fuzz. Test-point voltage right were they should be. I shut it down after about 40 minutes due to other demands. Next weekend, I will run it for several hours not on the Iso-Variac, and do leak tests, and re-test the various test points. I will also replace the line cord with a polarized cord so that the switch will directly switch the HOT - not that it should matter - and replace the fuse with a 1.5A dual-element rather than the 5A !! conventional fuse in place.

    It has already found a home - my son-in-law is interested. So, it must be properly set for polite society in that case, and I will also replace the outputs with truly matched pairs of Telefunkens that I have stored.

    I am not so sure, at this point, of whether or not I will replace the boards. This was a 'Factory (Drexel student) kit, with all the various parts-and-pieces riveted instead of screwed. Drilling out all those rivets, what with the marl to worry about getting into the pots and switches ... maybe not.  

    Again. Voltages are good, things are staying cool, no hum.

    Same Link as above now includes additional photos.

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