Sansui 350A troubleshooting discovery

[c.coyle]

Don't know how many of these are out there, and it looks like the following problem hasn't been discussed.

I picked up an all original Sansui 350A receiver from the late '60s or earlier '70s. The seller got rid of it because of low and distorted right channel output. This was true on all inputs when I ran it through speakers. But, when I listened through headphones, both channels were fine.

Unlike a lot of receivers with an OFF/A/B/A+B rotary selector, the 350A has a 2 position speaker toggle switch labeled simply A/A+B. A look at the schematic revealed that the speaker cut-off switch is an integral part of the headphone jack, and the amplifier output gets routed through it on the way to the speakers. Pushing in the headphone plug opens contacts for each channel and disconnects the speakers. A little deoxit and some pushing and pulling cleared it up. I'm glad, because the jack is probably unobtainium.

This is a cute little low power, cap coupled receiver. Built like a tank, as was all Sansui gear from that early period. Haven't yet cranked it up, but it seems to run cool. The sound is thin and tinny, so I'll do a recap, a complete power supply rebuild, and a replacement of the 2SC458s. No flying saucers in this one. It also has 8v fuse dial lamps, so they will become LEDs.

 

[Hyperion]

Yep, that problem has been mentioned fairly recently, well done on finding it

 

[Sansuiman]

Gave one of these to my brother who uses it in his workshop. A little beat up but works great (all original) and is a surprisingly strong little receiver. Don't know the actual specs on it but figure it is about 12 wpc. And in typical Sansui fashion, packs a lot of bang for the buck.

Glad you noted this design idiosyncrasy, as I wasn't aware of it. If it ever starts sounding "off" will need to check the headphone jack as the first order of business.

Kevin

 

[smurfer77]

I think this era of sansui receivers are my favourite so far. I have a few. I don't have the 350A but I do have a 350; the 350 is very very warm sounding, much like an AU-222 (I can't really think of another sansui integrated that sounds as warm as these receivers) so unless the 350A is very different to the 350 you most likely do need to replace some parts if yours sounds tinny. I'm looking forward to seeing your receiver getting some love; I think there is a too much (for my tastes anyway) emphasis on other receivers and i can only guess it's because they are higher powered or 'TOTL'

 

[c.coyle]

This is a later model 350A with a March, 1972 serial number. There were no 8002 / 9002 flying saucer transistors. Instead, 2SC875Es and 2SA532Es in TO-39 cans, which I replaced with ZTX694B and ZTX795A.

This thing has a hellacious turn-on thump that I need to address. Right after I got both channels working, I replaced the output caps with 2200uf in place of the original 1000uf. I should have listened to the originals with 2 good channels for comparison. I may put the 1000uf caps back in just to see if the thump remains.

 

[Roy Skinner]

Mr. Colye, you just made up my mind about working on my 2000, or 350A. Nothing like working on a unit that someone much more knowledgable has just worked on.
I used my 350A with Bose 301s for years. I had no idea it was considered low power, neither did my next door neighbor.

 

[Hyperion]

neither did my next door neighbor.

 

[smurfer77]

This is a later model 350A with a March, 1972 serial number. There were no 8002 / 9002 flying saucer transistors. Instead, 2SC875Es and 2SA532Es in TO-39 cans, which I replaced with ZTX694B and ZTX795A.

This thing has a hellacious turn-on thump that I need to address. Right after I got both channels working, I replaced the output caps with 2200uf in place of the original 1000uf. I should have listened to the originals with 2 good channels for comparison. I may put the 1000uf caps back in just to see if the thump remains.

I suspect the thump will remain.

 

[c.coyle]

I suspect the thump will remain.

Actually, the thump is gone. This goes under the heading of "did I do that?" I replaced the 2SC1081 regulator pass transistor in the power supply with a higher gain darlington, and, honest to goodness, next time I fired up, no thump. I wasn't trying to eliminate the thump with the new transistor, and I am sure it was thumping up to the moment I replaced the old one.

I have been trying to think of an explanation. Maybe the new transistor regulates the voltage faster on power up, causing the coupling caps to charge quicker or at the same rate? Maybe the old transistor was passing over voltage before regulation kicked in? I am stumped.

Because of the peculiar speaker switch configuration (see Post #1), I couldn't turn the unit on with speakers off and wait 10 seconds to see if it thumped on delayed speaker turn-on.

This is a lovely little receiver - sonically and visually - which I don't have room for, so it's probably going to get sold.

 

[smurfer77]

Actually, the thump is gone. This goes under the heading of "did I do that?" I replaced the 2SC1081 regulator pass transistor in the power supply with a higher gain darlington, and, honest to goodness, next time I fired up, no thump. I wasn't trying to eliminate the thump with the new transistor, and I am sure it was thumping up to the moment I replaced the old one.

I have been trying to think of an explanation. Maybe the new transistor regulates the voltage faster on power up, causing the coupling caps to charge quicker or at the same rate? Maybe the old transistor was passing over voltage before regulation kicked in? I am stumped.

Because of the peculiar speaker switch configuration (see Post #1), I couldn't turn the unit on with speakers off and wait 10 seconds to see if it thumped on delayed speaker turn-on.

This is a lovely little receiver - sonically and visually - which I don't have room for, so it's probably going to get sold.

Good stuff! I have a few receivers from that series and they all thump with original caps. Which transistor did you use?

 

[c.coyle]

Looks like it was a TIP141, but I am definitely not saying that that is what stopped the thump. It could have been a complete coincidence.

 

[Denf]

This is a later model 350A with a March, 1972 serial number. There were no 8002 / 9002 flying saucer transistors. Instead, 2SC875Es and 2SA532Es in TO-39 cans, which I replaced with ZTX694B and ZTX795A.

Hello CCoyle . I’m currently attempting to repair a 350a for a friend. His also has the same ‘flying saucer’ 875 and 532’s. I see where you indicated that you used the replacements listed above. My question (as a newbie!) the ZTX694 & 795 are both NPN, but the 532 is a PNP. Does this matter?

Did these replacements get rid of the issues you were having?

Appreciate your time and any help you can provide.

Thanks,

Dennis

 

[sregor]

Hello CCoyle . I’m currently attempting to repair a 350a for a friend. His also has the same ‘flying saucer’ 875 and 532’s. I see where you indicated that you used the replacements listed above. My question (as a newbie!) the ZTX694 & 795 are both NPN, but the 532 is a PNP. Does this matter?

Did these replacements get rid of the issues you were having?

Appreciate your time and any help you can provide.

Thanks,

Dennis

ZTX parts usually if first number even, then NPN, if odd, then PNP. So looked up both, in Mouser and ZTX795 is PNP, 694 is NPN.

 

[dly66]

With these old Sansui fresh electrolytic capacitors and replacing the noise prone vintage transistors with modern low noise ones yield a nice sounding unit. First had experience with the 800, 2000A, and 5000A all are relatively quiet in terms of background noise and I personally like the old Sansui cap coupled sound. Usually the old cap coupled designs thump on turn on but should not be obnoxious. On mine it is pretty mild.

 

[dlucy]

Hello CCoyle . I’m currently attempting to repair a 350a for a friend. His also has the same ‘flying saucer’ 875 and 532’s. I see where you indicated that you used the replacements listed above. My question (as a newbie!) the ZTX694 & 795 are both NPN, but the 532 is a PNP. Does this matter?

Did these replacements get rid of the issues you were having?

Appreciate your time and any help you can provide.

Thanks,

Dennis

@Denf as per AK rules, you should post a question in just one thread, not two.

 

[Denf]

Roger that and apologies. (Actually thought I was messaging to individual members).