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Sansui 555a - resistors replacement

H

harobike

New Member
Hi, everyone!
I did recently full recap in my sansui AU-555a. I want also to replace some transistors (CDC8002, CDC9002, XA495 and maybe 2SC281), but I began to wonder if I should not even replace all the carbon resistors for low noise metal foil resistors. Is it worth it? Or maybe it's just worse?
 
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It won't make a measurable difference. Replace the caps and the flying saucers and enjoy the amp. It's one of Sansui's best.

- Pete
 
Pete, 2SC281 is classified as flying saucers too? I understand that I do not have to replace the resistors, but should I replace the other not electrolytic capacitors?
I wonder also over the choice of transistors. Rob, comparing the characteristics of the original transistors with provided by you will see that they are much different. Why these transistors will be good substitutes?
 
The 2SC281 is not a "flying saucer" transistor, it is the bias control transistor (tubular metal can with three long wire leads. You can see the two of them from the bottom of the amp, they are attached physically to the heat sinks by a metal holder. If you replace these with the KSC1815 (TO92 plastic package) then you will need to make sure that you get a good thermal bond to the metal holder.

Cheers

John
 
Okay, the 2SC281 I replaced with a KSC1815 was probably in the 800 I did recently. So I may be wrong on that one.

When I restored my AU-555a I used the subs I posted. Since then, it's what I replace all the CDC8002/9002s I come across with. Work fine for me.

That's my pic of them above.

Rob
 
skippy124 said:
The 2SC281 is not a "flying saucer" transistor, it is the bias control transistor (tubular metal can with three long wire leads. You can see the two of them from the bottom of the amp, they are attached physically to the heat sinks by a metal holder. If you replace these with the KSC1815 (TO92 plastic package) then you will need to make sure that you get a good thermal bond to the metal holder.

Cheers

John
Click to expand...

The crucial thing about that T0-1 case transistor is that it has an isolated can, there is no contact with any of the 3 legs, which allows it to be in metal to metal contact with the heatsink(s). Because they are so hard to source now, that's what makes the T0-92 substitutes attractive because of the naturally isolated package - albeit plastic.
There are few transistors of other case styles with isolated metal cans, I believe some kinds of T0-39 case transistors are suitable.
 
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Thanks you so much for help:)
I only have a little problem. I'm from Europe actually and I do not have access to these transistors.
I searched such replacements:
CDC8002 - BC639 or BD139 ?
CDC9002 - BC640 or BD140?
XA495 - BC560 or BC556C ?
2SC281 - BC109 ?
Do you think that any of them will be good?
 
Interestingly, there is some anecdotal evidence from a few AKers who have tinkered with replacing carbon film resistors with metal film resistors in vintage Marantz gear, a NAD 3020 and a Sansui AU-D11 II from memory, and have noticed an improvement in clarity and resolution. In particular, the Marantz apparently sounded much less like an old Marantz! I don't think there was any data or measurements to back up these impressions, but the feedback was consistent from all three people who undertook the tweaks.

Food for thought anyway!
 
Just a note - don't handle the 2SC281 metal-can transistors unless you really have to - the leads can snap off at the base of the body fairly easily and then you are proper-fcked because it is hard to replace them these days.....just saying......I learned from experience with my AU-999.
 
harobike said:
Thanks you so much for help:)
I only have a little problem. I'm from Europe actually and I do not have access to these transistors.
I searched such replacements:
CDC8002 - BC639 or BD139 ?
CDC9002 - BC640 or BD140?
XA495 - BC560 or BC556C ?
2SC281 - BC109 ?
Do you think that any of them will be good?
Click to expand...

Hi,

For the CDC8002, use BD139
For the CDC9002, use BD140

The KSA2690/KSA1220 as Rob posted above are better subs,mount I have use the BD's without a problem

XA945 - use BC560C (BC560 would be better the XA945's that I have measured have all had gains ranging from 140 to 200)

For all,of the above, be careful of the different in pin outs between the original and replacement transistors

Re the 2SC281, why do yo need to replace these - are thy damage or faulty?

Cheers

John
 
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Hi!
Thank you Skippy for your answer. In that case, I buy BD139, BD140 and BC560C (you wrote XA945, I think that you mean XA495?).
I don't really know if my transistors (2SC281 too) are good or not.. I do recap in my Sansui 555a and when I turned it on, I noticed that there is much less noise (nice!) but still one channel is worse than the other. It's muddy and quieter. Do you know which transistors may be responsible for this?
 
I wouldn't look at the 2SC281's unless your bias is hard to set, then that could be an issue with one of these trannies, and you should test it in that case. With your "muddy and quieter" channel - is this after u did the recap work? Double check at all your new cap polarities, check all connections, ensure all your knobs & switches are as clean as u can get them.
 
One channel was muddy and a little bit quieter before the recap. After that, unfortunately it doesn't improved in this regard.
I hope that after exchange CDC8002, CDC9002 and XA495 everything will be fine.
 
And even going back to what pete_mac wrote; I read that it may be well to replace the carbon resistors with metal film resistors in the preamplifier section. What do you think?
 
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