Sansui AU-317 Restoration: Zener question

[dedero]

Hello All,

I'm actually doing a restoration of a AU-317 which is in a very good condition and never opened (it seems), performing a full recap, relay change, replace carbon for metal film resistors (including fuse resistor ones), pot cleaning and checking all broken/cold solder joints.

Everything is going fine (although I'm still struggling with the deadly glue) until I found out yesterday that there is a pair of never seen Zener diodes:

ZD601 is totally fine, with the corresponding Zener as per service manual.
ZD602 has a pair of ITT ZX15 instead of the same Zener as ZD601 (should be exactly the same ones as per service manual)

AU317_Double_ITT_Zener

• dedero
• Feb 25, 2019

ZD601 = 2x ZX15 ITT Zener instead of the original EQA01-30R

Any ideas/experiences with this?, I'm planning to replace ZD601 and ZD602 with 2 new pair of Zeners 1N5256B (https://www.mouser.de/ProductDetail/78-1N5256B) and I also realized that the actual ZD601 is a black one when the new 1N5256B are the small red ones, as far as I understood the black are the "normal" diodes and the red ones are the zeners...

Sorry for the confusion I'm quite new with restorations and I tried to collect all information from the forum for this restoration but it seems it's not enough...

Any help will be appreciated!

Cheers,
Bruno.

 

[Hyperion]

I'm planning to replace ZD601 and ZD602 with 2 new pair of Zeners 1N5256B (https://www.mouser.de/ProductDetail/78-1N5256B)

Yes, do that - those metal cased monstrosities need to go.

and I also realized that the actual ZD601 is a black one when the new 1N5256B are the small red ones, as far as I understood the black are the "normal" diodes and the red ones are the zeners...

This may be the case sometimes - but do not use the colour of semiconductor components as a guide. I can show you 2 diodes side by side which look identical, both clear glass and red coloured inside, and one is an ordinary diode and the other is a zener. Similarly with the black/grey plastic encapsulated types - exactly the same thing applies.

 

[Leestereo]

...I'm planning to replace ZD601 and ZD602 with 2 new pair of Zeners 1N5256B (https://www.mouser.de/ProductDetail/78-1N5256B)...

Consider using this 2%, low-noise, very high stability (as per data sheet) 30V zener replacement: https://www.mouser.de/ProductDetail...=sGAEpiMZZMtQ8nqTKtFS/KE3JtglsWdkGWVTmel/wHE=

 

[dedero]

Yes, do that - those metal cased monstrosities need to go.
This may be the case sometimes - but do not use the colour of semiconductor components as a guide. I can show you 2 diodes side by side which look identical, both clear glass and red coloured inside, and one is an ordinary diode and the other is a zener. Similarly with the black/grey plastic encapsulated types - exactly the same thing applies.

"those metal cased monstrosities need to go"

Thanks for the info!, I thought so about the materials and colors for diodes but I just wanted to make sure!

Consider using this 2%, low-noise, very high stability (as per data sheet) 30V zener replacement: https://www.mouser.de/ProductDetail/Vishay-Semiconductors/BZX55B30-TR?qs=sGAEpiMZZMtQ8nqTKtFS/KE3JtglsWdkGWVTmel/wHE=

Thanks for the hint!, I was taking a look in digikey and several distributors here in Germany and nobody have stock for it... the only one is Mouser but they're charging 20eur shipping for 2 diodes... it's a pity but I'm afraid I will go for the mentioned Zeners, I will keep the stability feature in mind for the future!

 

[Bob]

just as a side note - you may wish to keep the carbon comp/film in the sound chain.

I have noticed over the decades, looking/reading Japanese audio unit's schematics, that
they are predominantly non- metal films. I speculate that this is there "house-sound" voicing.
Because there so many, very few folks swap them out, and they tend not to go out of range.

On the other hand, I have modified many Hafler dh-101s and replaced all carbon resistors
with metal films. the sound stage gets spooky dark. and even here with fewer resistors
there are few folks who replace them but when done, the sound changes for the better.

before the deniers jump in, when you buy millions of resistors, the difference between
the various resistors is far, far less than the cost of the chassis, front panels, knobs, etc