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Project: SX-1250 (2nd Take)

I Should Stop Buying Vintage Units - What is My Problem?

  • Sick

  • Not Right Upstairs

  • Sucker to For What Lots of Folks Refer to as Junk

  • Easily Hypnotised By Brushed Aluminum

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Film caps don't usually fail, unless there is a darn good reason to change them I would leave them alone. That is not a high voltage circuit that might have punched a hole through the dielectric film. Factory changes during production (unless major) almost never make it into field documentation.
 
I was thinking about better sound quality with the polypropylene cap . This cap is the input on the base of the first differential pair transistor .

>>>>>> It appears Pioneer may have had a parts shortage on this run. The 470 caps on this board caps are different one is the LL yellow and one the standard black color. Made July 1977 .
Wonder why the change from 2.2uf to 1uf .
 
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Maybe a parts shortage, the -3db point is about 1 Hz for the 2.2µF, and about 3.5Hz for the 1µF if I calculated it correctly. Can't see any frequency response reason to change, they are just dc blockers.
 
Super Noob said:
Final Pics:
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Looks as good as it sounds. Hope these posts inspire some folks to rebuild their SX-xx50 receivers.

Best Regards & Thanks for Viewing.
Click to expand...

My Goodness, that is beautiful. What a labor of love.
 
markthefixer said:
Rumble? Rumble filtering? (phono)
Click to expand...
That is as good a thought as I could come up with. When I got my NEW SX-1050, I also got a Garrard Zero100c. I bought a copy of Dark Side of the Moon that had a warped edge, like it had leaned at an angle in a hot environment. When I played it I could see the woofers motoring in and out on my Infinity Column II speakers. When I took it back for replacement the shop owner put it on his shop system and his woofers did not move. I am guessing that was about a 3Hz signal, but it was about a 1/4" hump in the vinyl. :dunno:
 
I'm done working on the boards time recheck and reassemble this Sx1250 and DBT test it . I did find a few discrepancies with tuner board BOM . C33,C48 . By looking at the finished tuner board picture they appear to be typo's.
 
I am restoring another SX-1250. I am at the equalizer board, what do you think about using one 10uf BP (ES) cap for the two 22uf back-to-back tantalum caps? FYI, I measured. The tantalum caps and they're @ 200uf.and 100uf, I used to different testers. I thought it was displaying NF. it wasn't.
 
I won't need the 50V ratting that the back-to-back caps have? I don't want play around with the uF I'm not sure what it will change.
 
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When your are talking components in a design, specify the exact ones on the schematic, BOM rather than guessing what ones you are referring to
the two 22uf back-to-back tantalum caps meaning, C25,26,30,31, two 22uF/16V in series = 11.5uF/32V
if you want BP, then use 22uF/35V, 647-UES1V220MPM, its not currently EOL
https://www.mouser.ca/c/passive-com...citors-radial-leaded/?q=UES&capacitance=22 uF
Nothing wrong with using two UKL back to back either, need to check what's available now
This is the list I have, it old, probably derived from Mark and others, many Nichicon could be EOL, its been years
AWF-021-A: C11: 470uF 6.3v CEANL: 647-UKL1C471KPD 470uF 16v
AWF-021-A: C12: 470uF 6.3v CEANL: 647-UKL1C471KPD 470uF 16v
AWF-021-A: C17: 3.3uF 50v CEANL: 647-UKL1H3R3KDDANA 3.3uF 50v 505-MKS2B043301H00KI
AWF-021-A: C18: 3.3uF 50v CEANL: 647-UKL1H3R3KDDANA 3.3uF 50v 505-MKS2B043301H00KI
AWF-021-A: C25: 22uF 16v CSZA: 647-UKL1V220KEDANA 22uF 35v
AWF-021-A: C26: 22uF 16v CSZA: 647-UKL1V220KEDANA 22uF 35v
AWF-021-A: C27: 220uF 63v CEA: 667-EEU-FC1J221 220uF 63v
AWF-021-A: C28: 220uF 63v CEA: 667-EEU-FC1J221 220uF 63v
AWF-021-A: C29: 100uF 35v CEA: 667-EEU-FM1H101 100uF 50v
AWF-021-A: C30: 22uF 16v CSZA: 647-UKL1V220KEDANA 22uF 35v
AWF-021-A: C31: 22uF 16v CSZA: 647-UKL1V220KEDANA 22uF 35v
AWF-021-A: C32: 100uF 35v CEA: 667-EEU-FM1H101 100uF 50v
 
Right If two 22uf /16v =11.5uf /32v Shouldn't I use one 10uf /35V BP? Is 35V really needed here? What is the advantage of using back-to-back? I'm thinking a 10uf BP cap was too costly in 1978 and a film cap just too big. I thought I was clear on what caps, I'll put the numbers next time.
 
I stayed with the four 22uf/35v for C25,26, C30,31 .
I do have an DC offset problem. The DC offset is low but is fluctuating fast and I get a split second spike that gets higher over time, 15mV so far. My differential pairs hfe on the amps inputs are close within 6 or 7 points. Defeating the tone controls helps. Checking my work, any ideas?
 
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