Re: the evil Hitachi 2SC458 transistor

62vauxhall

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#1
If anyone likes to tinker with old junk like me, don't believe the data sheets. They show a pin configuration of ECB but that is not correct. At least it isn't for early squarish 2SC548 with the beveled top. Those are actually BCE. It seems that when they changed the shape from square to round the pin arrangement changed as well to ECB.

This has just now confounded me while fixing an Akai CR-83D with a bad noise problem. Having learned through an Akai GX4000 of the existence and reputation of 2SC458's, I figured it likely there were some in the CR-83D and there were - four of them.

I put in replacements with the same pin configuration as per the data sheet but there was no sound of any kind afterwards. I scoured forum threads and found one from 2009 on AK which explained this discrepancy. The GX4000 had fourteen of those things and I did replace them all but I can't remember reversing them. Maybe i did and just forgot in the intervening time - memory is the first to go they say.

In any case after reversing the transistors i just put in, the CR-83D plays fine now.

2SC458's were supposed to have been used by many Japanese manufactures in the 1970's not just Akai - Marantz, Sansui, Pioneer, Kenwood etc. I just thought it worth mentioning the irrelevancy of the datasheet in case anyone runs into this same dilemma.
 

orange

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#2
Are you sure it wasn't just a dumb mistake by some manual writer in Japan?
 

62vauxhall

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#3
Nope. This is part of the 2009 post in the AK thread I read earlier today. Poster's handle was Fred Longsworth:

"The original 2SC458 was made by Hitachi, and installed in a funny-looking rectangular package with a little "roof" on the top that slopes down from front to back. These were based BCE reading left to right. At the time of manufacture, these were considered an excellent choice for a low-noise, small-signal transistor -- and were used widely. Unfortunately, they began to leak and generate noise and operating-point errors".

"A few years ago, "new generation" 2SC458's began appearing. These were in a more modern package -- like the 2SC2240, which read ECB from left to right. I consider many of these "new 2SC458's" to be counterfeits, i.e. other transistors relabeled".
 

orange

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#5
There have been some substitutions for this transistor for a long time I think, although maybe not all applications.

I wonder if my Pioneer QX-8000 has any? I had two and the one I tore down had noise problems such as that.
 
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8991XJ

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#6
Could it be that the slanted roof units are ECB from the short face, not the named face and the TO-92 style are ECB from the flat named face? I don't know if there is a naming convention for the slanted roof transistor types that would make it the side to read.
 

62vauxhall

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#7
AFAIK, transistor pin designation is standardized L to R while looking at the name side in all cases. With "slant roof" Hitachi's, the name is on the wide side. In the case of those I just pulled, there is printing on the other side too but it must be a date code or something. I had to look closely because at first glance, because they're so small, I could have easily mistaken back for front, just looking for writing.

Substitutes that I read were acceptable were 2SC2240 and KSC1845. I understand 2SC2240's have been out of production for a while and when forum searching this recent repair, learned KSC1845's are discontinued now too. I used KSC1845's because I have more of them than 2SC2240.

I don't know when 2SC458's went from "flat roof" to round, but the round one's may not be susceptible to the same problem. Those that I've encountered all had black oxidized legs. Although that in itself may not an issue, if I see that, I will change it out.

Speaking as a lay person, if anyone here plans on revitalizing pretty much any 1970's decks/receivers/amps, it would be a good idea to lay in a supply of KSC1845's while they're still available.
 
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