Standard SR-157SW

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Hi,
Has any of you ever heard of the (Norwegian? Japanese?) brand Standard? And if, of the SR-157SW amplifier? It's a 2x7.5W amp.

I have picked up one of these at a second-hand store and put it in the kitchen as lo-fi amp. But, after opening it up a minute ago I saw it has AD149 and 2SB449 germanium BJTs in it :). After searching, I could only find some images but no information at all. The name Standard makes it a hard search...

Does any of you have some information? Data, manual, anything really!? The board is very densily populated, so it'll cost me some time figuring out the circuit...

Some pictures can be seen at:
http://www.electricalhobby.com/unit_pages/standard_SR157SW.htm
http://www.audiokarma.org/forums/showpost.php?p=950713&postcount=84
 
No-one? Still?

Yesterday I replaced all large electrolytics (> 22 uF), making it sound much better. But, it still has some issues with low frequency sounds, which are a bit harsh and distorted... Could this be leaking Germanium transistors? Or should I replace the very small electrolytics as well?
 
you have to

replace all electro's inside without even thing anything about them

you also might wana take a look here
http://www.diyaudio.com/forums/showthread.php?s=&threadid=136261&highlight=e

to be honest with you since i am 42 that device from looks rings a bell but nothing else ....it seems to me that i ve seen this sometime in the past like 25 years ago in a parts shop but with another brand name .....
 
take

a look at that

a JVC 4 channel amplifier ..... removed all caps from it after 30years .....

only four of them where within specs

its these elna's that have red marks on their tops these particular caps are sealed so they never fail ...
 

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Thanks sakis! I'll replace all 'lytics next weekend and have a look at the huge list of improvements you mention in the other post..

So you've seen this amp you think, that's great :). I thought it might have been an amp of which only a few were built, since it has some DIY artefacts to it. The wooden case looks as if it were built from some board somebody had lying around, no screw is the same, pcb traces are all tinned and wires are very carefully assembled, again with all kinds of different material. Could be a rework job ofcourse, since I noticed that (probably) two of the AD149's have been replaced by 2SB449's..
 
Alright, I promiss you now I'll do this next weekend! Since I am away for the week there's no time to do it today... I was already planning on drawing it myself, so I will...

Have patience, and you'll get a nice germanium amp :). What I figured out (might not be true):
- 2*PNP output stage w/ AD149 (don't know the topology)
- driver stage/VAS w/ 2SB33 (Ge, P) and 2SC967 (Si, N) --> Strange! (might be a replacement, therefor I want to have a manual!)
- single 2SC372 (Si, N) differential amp (possible?) or VAS

The output signal is fed back to this first stage (2SC372) and as I remember to an even earlier stage as well. But, it'll all be clear next weekend!
 
I got a schematic from the Norwegian guy! It was a bad scan, so I redrew it :). I could've made a mistake, but I'm pretty sure it's right the way I drew it. It's a strange topology to me, but you might be able to figure it out! Please have a look and comment on it freely...
 

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AD149, because Germanium, is biased having only 200 milivolts from base to emitter

If you replace this transistor with another one... a non germanium transistor, them you will have strong distortions, in special while reproducing low level..low volume.

I am not sure about this 2SB you told... i am not sure if the unit is Germanium or not.... you must search into internet to be sure.

AD149 was a low gain unit, used as Voltage amplifier in many amplifier, and as i could remember it was almost unique... substitution resulted bad.... i think some guys have used AD161 or AD162 (the PNP unit i think) to substitute when the AD149 started not to be found into the electronic shops (1973)..it became a rarity..was a problem... was a not easy to find a good substitute to that transistor.

I have used many times..and i found this transistor as very nice... copper case..heavy unit...Chromium cover.... good fellow that one.


Was used into automobile radio receivers output.... 2 to 4 watts RMS output.

Silicon transistors needs more voltage from base to emitter... more than 500 milivolts, more often used is 600 milivolts when the standard is 650 milivolts from base to emitter.

So.... removing a Germanium unit and entering a Silicon unit into the place will produce enormous mess with the sound quality...will be harshing, distorting alike crazy.... to do that has to change something to increase voltage to the base.... increasing the resistance from base to ground...or from base to the rail power line, in order to have developed over that resistance more than 500 milivolts.... it is an increase of value of resistance, to increase voltage to that transistor base.... or changing the bias trimpot adjustment to increase current into the system when using AD149 as driver or output.

I am not sure if this is what is happening...maybe your 2SB is a Germanium unit too....you must check that.

Carlos
 
Yep... the AD149 was used in this kind of schematic down the seventies and sixties

And the unit was more often used as voltage amplifier, in the place you see the red circle.

It was used into older style schematics that had not the differential amplifier into the output... the one is very old, but this does not means sounds bad...the opposite..sounds excelent.

The resistance, into the input used to be adjusted in such way to "develop" 200 milivolts to the transistor base to emitter junction..so..it was smaller than the one you see...maybe 270 ohms,

To use the Silicon, they had to increase this resistance value in order to develop more voltage, and this was needed to "force" the unit to conduct.

regards,

Carlos
 

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