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Pioneer SX-636 - Rebuild and Speakers

Rob Wain

Rob Wain

New Member
Hi. I've used the great info you Gents/Ladies' post here to start the rebuild on my SX-636 and PL-12D turntable. Like most, this was the kit my Dad had when I was a kid (the turntable was his, the amp is beyond repair so I have a new to me unit from eBay).

They both work pretty well, but I started to get popping from the right speaker, intermittently, only lasting a few seconds and no influence from the volume control. I only have cheap Pioneer bookshelf speakers from an old stereo I had in the dining room. The right speaker is now not working.

So I've replaced the two 2SC1451 with ONSEMI KSC3503DTSU and the blown 4amp fuse. I've also replaced all the caps on the power supply board.

All is working as I write, but I have some more parts ready to go in if I need to (including some KSA992 that I've got matched pairs collected together).

I do have 3 questions though:

1) Does DC current gain matter on transistors (I realise it does for differential pairs) ? I'm looking at the power supply, and in particular the 2sd234 for which the KSC2073TU are listed substitutes. However, ONSEMI no longer make these KSC2073TU, but do have KSC2073H2TU. The only difference being the DC current gain (KSC2073TU - 40hFE; KSC2073H2TU - 60hFE).

2) What do people recommend for cleaning the flux off the board after you have installed the new components?

3) What bookshelf speakers should I buy for the system? I would like some period Celestion Ditton speakers (Dad had 44s). However, until I find a reasonably priced pair, I will buy some new speakers to get me up and running again. Looking to spend about £125 max. I cant afford them to be too big, as its all in my home office, and not much room left!

4) I know I said 3, but I thought of another. How do I tell which manufacturer/component is best for audio grade?

Thanks for any advice you can give.

Rob (England)
 
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Welcome Aboard!

Regarding the regulator (pass-regulator) transistors in the power supply, current gain is less of a factor in selecting replacements for this application, but it is still a factor. The schematic shows the 30V supply has a design load current of around 25 mA. If a pass transistor installed in that application (Q1) has an hFE of 10, the theoretical base current for that transistor would be approximately 2.5mA. As long as the transistor operating the base of Q1 has a collector current rating above 2.5mA, everything should be acceptable. Of course, we always like to apply some safety factor, so if Q2 has a collector current rating of 100mA (as it does) and Q1 has a minimum gain factor of 40, the load of the 30V supply could be 4A before Q2 is stressed. That's a lot of reserve capacity, but generally good design practice.

In short, selecting a replacement for Q1 should be based on the maximum collector current of that device, the voltage rating of that device, and a gain factor sufficient to keep Q2 in a safe operating range. I would suspect that anything over a 20 hFE would work reliably.

A KDS526Y, MJE15030G, or that KSC2073H would work, along with a host of others, like MJE15032G, TIP41C, BD241CG.
 
As for flux removal, there are specific products sold to remove flux, but some of those can be detrimental to some of the plastics and imprinting encountered in older equipment. An isopropyl alcohol solution and swabs or a stiff brush can be used successfully, and they are readily available from your local chemist or market.
 
The speakers are as much a matter of preference as specification. What speakers are presently in use? They might not be all that bad for a moderate power system such as this, at least as a beginnning.
 
Watthour said:
Welcome Aboard!

Regarding the regulator (pass-regulator) transistors in the power supply, current gain is less of a factor in selecting replacements for this application, but it is still a factor. The schematic shows the 30V supply has a design load current of around 25 mA. If a pass transistor installed in that application (Q1) has an hFE of 10, the theoretical base current for that transistor would be approximately 2.5mA. As long as the transistor operating the base of Q1 has a collector current rating above 2.5mA, everything should be acceptable. Of course, we always like to apply some safety factor, so if Q2 has a collector current rating of 100mA (as it does) and Q1 has a minimum gain factor of 40, the load of the 30V supply could be 4A before Q2 is stressed. That's a lot of reserve capacity, but generally good design practice.

In short, selecting a replacement for Q1 should be based on the maximum collector current of that device, the voltage rating of that device, and a gain factor sufficient to keep Q2 in a safe operating range. I would suspect that anything over a 20 hFE would work reliably.

A KDS526Y, MJE15030G, or that KSC2073H would work, along with a host of others, like MJE15032G, TIP41C, BD241CG.
Click to expand...

Very detailed answer, thank you.
Is there any need to change the transistors if I now have no issues? I've re-capped the power supply, should I leave the transistors etc?
 
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Watthour said:
As for flux removal, there are specific products sold to remove flux, but some of those can be detrimental to some of the plastics and imprinting encountered in older equipment. An isopropyl alcohol solution and swabs or a stiff brush can be used successfully, and they are readily available from your local chemist or market.
Click to expand...

I have some iso. alc. in the workshop, will use that then. Thank you.
 
If the power supply is working now, there should be no need to change the transistors just because they are original.
 
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