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    SCA-35 Selector Switch

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    Tom_Johnson
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    SCA-35 Selector Switch

    Post by Tom_Johnson on Tue Nov 27, 2018 3:08 pm

    OK Guys, please bare with me for a minute. I picked up a factory wired SCA-35. Upon inspection, I found one of the selector wafers is broken beyond repair, 3 parts, spent hours trying to fix it. Done with that.
    Since this is a shorting type selector (for no cross talk between components) and made just for this amp, it is Irreplaceable so be careful with what you have. I started looking around and there is nothing that is compatable or, drop in ready. I contacted a couple companies that make selector switches, for them to R&D the switch is way to much $$$. Since the original is a double wafer switch, it is more akin to a 4 pole 5 throw switch. I purchased a couple of these Russian selectors seen below. I was thinking with a few modifications, It might work. Any thoughts would be greatly appreciated. Thanks, Tom


    peterh
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    Re: SCA-35 Selector Switch

    Post by peterh on Tue Nov 27, 2018 3:29 pm

    You might have more fun with an relay board, which may be bought cheap on ebay :
    4 channels :
    https://www.ebay.com/itm/Switch-Signal-Selector-Audio-Input-Signal-Amplifier-Board-Board-Relay-DIY/222466373655?hash=item33cc077817:g:Ao4AAOSw03lY554O

    or 6 channels
    https://www.ebay.com/itm/6-Channel-Unbalanced-Stereo-or-Balanced-Mono-Audio-Input-Selector-Relay-Module/201225517448?epid=1382862099&hash=item2ed9f9b988:g:bMMAAOSwBadTq6UA

    Both may be rebuilt ( if not already ok) so the unused inputs are shorted to ground.
    Board may be mounted at the back, switch mounts in it's usual place. 12V may be created by
    doubling the filament.
    Tom_Johnson
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    Re: SCA-35 Selector Switch

    Post by Tom_Johnson on Tue Nov 27, 2018 4:34 pm

    Thanks peterh, I saw another post where you said this could work, I need to research the shorting or map it somehow. I understand the concept, implamenting it is the challenge.
    Cool avatar by the way. Whats the story?
    peterh
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    Re: SCA-35 Selector Switch

    Post by peterh on Tue Nov 27, 2018 5:53 pm

    Tom_Johnson wrote:Thanks peterh, I saw another post where you said this could work, I need to research the shorting or map it somehow. I understand the concept, implamenting it is the challenge.
    Cool avatar by the way. Whats the story?
    The avatar is a graffiti made by an unknown artist in a railway tunnel. Long gone,
    i think my fotos is the only memories. I found it appealing.

    Tom_Johnson
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    Re: SCA-35 Selector Switch

    Post by Tom_Johnson on Tue Dec 18, 2018 7:14 pm

    I did some clean up on the original drawing for the SCA-35 selector switch. This is one side (A side) with front and back of waffer shown. Now to figure out how to make something else work in its place. The Russian ones above will not work the way I thought after studying the drawing further. It would be cool to make a board similar to the one peterh suggested to do this job.


    Tom_Johnson
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    Re: SCA-35 Selector Switch

    Post by Tom_Johnson on Tue Dec 18, 2018 7:41 pm

    This is the side A Preamp


    WLT
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    Re: SCA-35 Selector Switch

    Post by WLT on Tue Dec 18, 2018 9:59 pm

    Finding a parts amp would be the easiest source. Finding a parts amp might be pretty difficult though. Long ago I had one but the parts are gone now.

    I will check with a friend of mine who may have one.
    Tom_Johnson
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    Re: SCA-35 Selector Switch

    Post by Tom_Johnson on Wed Dec 19, 2018 10:48 am

    Thanks WLT
    Peter W.
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    Re: SCA-35 Selector Switch

    Post by Peter W. on Wed Dec 19, 2018 12:50 pm

    https://www.alliedelec.com/electroswitch-inc-d2d-51/70152358/?mkwid=sjXpftxgT&pcrid=30980760979&pkw=&pmt=&gclid=CjwKCAiA9efgBRAYEiwAUT-jtCK3GM_b0n8UpwtjOMje5EIdpSW35vr97aaXnuGTF9715toTtpoaNRoCrqgQAvD_BwE

    Long link - but you could actually create a replacement from OTC parts. A major PITA, but entirely possible.

    I have gotten all sorts of stuff from this source - and adapted it with various combinations and permutations of surgery and jumpers:

    https://www.surplussales.com/switches/SWRoMisc-2.html

    Were I to find an SCA 35, I would be extremely hesitant to junk it, and far more likely to attempt to restore it.

    Good luck with it!
    Tom_Johnson
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    Re: SCA-35 Selector Switch

    Post by Tom_Johnson on Wed Dec 19, 2018 4:09 pm

    Thanks Peter, I looked and if I could make a 10P5T, It could be done and have the tape head like the original. It is the grounding scheme that is so hard to replacate.
    Peter W.
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    Re: SCA-35 Selector Switch

    Post by Peter W. on Wed Dec 19, 2018 4:14 pm

    Rotary Switch
    17P3T

    Shorting functions built in, more than you need. And a 12-pole switch front-back.

    You would use an X-Acto or similar to cut the traces as-needed to duplicate the pattern on the OEM.

    Been-there-done-that. Fully agreed on the PITA part.
    WLT
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    Re: SCA-35 Selector Switch

    Post by WLT on Wed Dec 19, 2018 10:35 pm

    No spare part switch readily available. The parts amp should be at my friends place but buried and not easily found.

    It was on a unit with no transformers, or covers. Not sure it even had circuit boards. But I remember it had some switches.

    Sorry
    Tom_Johnson
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    Re: SCA-35 Selector Switch

    Post by Tom_Johnson on Thu Dec 20, 2018 11:40 am

    Thanks WLT for looking around. I only need one waffer if anything turns up.
    Tom_Johnson
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    Re: SCA-35 Selector Switch

    Post by Tom_Johnson on Sat Dec 22, 2018 11:57 am

    I went ahead and purchased two 6 Channel Unbalanced Stereo Audio Input Selector Relay boards that peterh suggested. I will just use 5 channels and will install a 2p5t selector switch. They are not big at all (3.86 x 1.97 x 0.63 inches).


    Tom_Johnson
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    Re: SCA-35 Selector Switch

    Post by Tom_Johnson on Sat Dec 22, 2018 2:11 pm

    The other board will help me finish a conversion of a junk Pat 4 to some type of Pas preamp. I will know more when I get the boards. Looks like some trace cutting and Relay lifting may be involved. Better order a couple extra relays just in case.
    tubes4hifi
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    Re: SCA-35 Selector Switch

    Post by tubes4hifi on Sun Dec 23, 2018 9:13 pm

    that's the best and easiest solution, Dynaco always had to complicate things with their preamp switches,
    I've always just tossed them in the trash and used a common 2P6T shorting rotary switch,
    but you don't get the "special" connections that way, (does anyone use special connections anyway??)
    Tom_Johnson
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    Re: SCA-35 Selector Switch

    Post by Tom_Johnson on Mon Dec 24, 2018 11:11 am

    The special connection is on the Pas. and it is a 6T switch. The SCA-35 is a 5t switch and the tape head could be removed and made into another phono output. I have 8 track tape decks, cassette decks and a couple reel to reels. Do I use them much, no I don't. If I can't make this work, I will eliminate the tape head. I also ordered a couple 2 channel  DPDT Signal Relay Module Boards. I was thinking (Dangerous) maybe come out of one relay on the 6 channel board and into one of the relays on the 2 channel board with the Resistor and Capacitor on the ground between the two. The boards are activated by the power supply ground through the selector switch, according to the schematic.
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    audiobill

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    Re: SCA-35 Selector Switch

    Post by audiobill on Mon Dec 24, 2018 6:41 pm

    tubes4hifi
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    Re: SCA-35 Selector Switch

    Post by tubes4hifi on Thu Dec 27, 2018 2:43 pm

    audiobill,
    just a note for someone who might wonder why you do this . . .
    so you are replacing a simple switch, for a simple switch connected to a bunch of relays.
    Anyway, for the original thread, replacing a complex switch with a simple switch connected to a bunch of relays.
    Very Happy
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    audiobill

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    Re: SCA-35 Selector Switch

    Post by audiobill on Thu Dec 27, 2018 8:48 pm

    I guess I'd prefer that the actual audio connections take place inside a modern sealed relay switch than through a corroded, phenolic antique that was worn out decades ago....unless one believes that's the key to "vintage" sonics............the front panel switch is just a relay energizer, no audio involved.
    peterh
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    Re: SCA-35 Selector Switch

    Post by peterh on Fri Dec 28, 2018 9:47 am

    tubes4hifi wrote:audiobill,
    just a note for someone who might wonder why you do this . . .
    so you are replacing a simple switch, for a simple switch connected to a bunch of relays.
    Anyway, for the original thread, replacing a complex switch with a simple switch connected to a bunch of relays.
    :D
    Relays may be located right at the incoming connectors, no long wires hanging
    across the amp. Short signal cables, That's a clear plus for me!

    Relays are easily replaced if needed, and a future benefit is that they might be
    remote controlled ( if needed=

    peterh
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    Re: SCA-35 Selector Switch

    Post by peterh on Fri Dec 28, 2018 12:27 pm

    The best relays i have found is mercury-wetted potted DIL relays. Unfortently mercury is banned
    and those relays are unobtainable. The potted relay screen is easily interconnected by a grounding
    strip, thus screening from outer hum sources or interferens.
    The mere act of controlling them via 5V ( or 12V ) DC invites to easier control. One such example was
    a before/after switch for not one but two tape recorders using only a on-off-on two pole switch.

    Peter W.
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    Re: SCA-35 Selector Switch

    Post by Peter W. on Fri Dec 28, 2018 1:09 pm

    peterh wrote:The best relays i have found is mercury-wetted potted DIL relays. Unfortently mercury is banned
    and those relays are unobtainable. The potted relay screen is easily interconnected by a grounding
    strip, thus screening from outer hum sources or interferens.
    The mere act of controlling them via 5V ( or 12V ) DC invites to easier control. One such example was
    a before/after switch for not one but two tape recorders using only a on-off-on two pole switch.


    They are not banned in the US, and are readily available as current stock.

    http://relays.struthers-dunn.com/viewitems/reed-relays/134-series-mercury-reed-relays

    https://www.mouser.com/Search/Refine.aspx?Keyword=mercury+relay

    And in Europe.

    https://www.willow.co.uk/Mercury-Contactors/View-all-products.html

    Not cheap.
    peterh
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    Re: SCA-35 Selector Switch

    Post by peterh on Fri Dec 28, 2018 1:16 pm

    Peter W. wrote:
    peterh wrote:The best relays i have found is mercury-wetted potted DIL relays. Unfortently mercury is banned
    and those relays are unobtainable. The potted relay screen is easily interconnected by a grounding
    strip, thus screening from outer hum sources or interferens.
    The mere act of controlling them via 5V ( or 12V ) DC invites to easier control. One such example was
    a before/after switch for not one but two tape recorders using only a on-off-on two pole switch.


    They are not banned in the US,  and are readily available as current stock.

    http://relays.struthers-dunn.com/viewitems/reed-relays/134-series-mercury-reed-relays  

    https://www.mouser.com/Search/Refine.aspx?Keyword=mercury+relay  

    And in Europe.

    https://www.willow.co.uk/Mercury-Contactors/View-all-products.html  

    Not cheap.

    That was good news ! Thanks !
    Tom_Johnson
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    Re: SCA-35 Selector Switch

    Post by Tom_Johnson on Thu Jan 17, 2019 3:23 pm

    The Relays have landed and are being shipped from Chicago so they should be here soon. I emailed Dave Gillespie at tronola.com about replacing, rebuilding the PEC modules in the SCA-35. Dave said "Generally no — unless testing indicates that there is an issue with a PEC, which has rarely ever happened. I’ve found that at least with this amplifier, the PECs typically run quite true to their intended internal values, so that the balance through the tone control section is usually quite good"

    I had already cleaned up the PEC schematics just in case.




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