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2sc458, 2sc2240 Clarification please

Yankee Dog

Yankee Dog

Well-Known Member
OK, so I am going to replace the leaky 2sc458 (6 of them) in my 2220 when the new trannys arrive next. I ordered the 2sc2240 as a replacement from MCM.

I read a thread on this forum that stated something to the effect that the 2sc2240 has "opposite basing" than the 2sc458. Then a similiar thread mentions to "put them in backwards". The post was made by someone who is well respected and very experienced in this forum, so this is my reasoning for questioning what I have found in the data sheets.

So looking at the data sheets I am not seeing it. It looks like a direct drop in. Not backwards, or whatever:

http://www.audiolabga.com/pdf/2SC2308.pdf

http://www.datasheetcatalog.org/datasheet/toshiba/968.pdf

Am I a dope and just reading it wrong? I really want to be sure before I put these things in. Thanks, YD
 
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Dear friend:

transistor basing are the same for both 2SC458 and 2SC2240, but there are most suitable transistors to replace 2SC458 LIKE 2SC1815 , 2SC945 ETC.

i upload a Transistor Substitution data book about 2SC458
 

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lalomarantz said:
Dear friend:

transistor basing are the same for both 2SC458 and 2SC2240, but there are most suitable transistors to replace 2SC458 LIKE 2SC1815 , 2SC945 ETC.

i upload a Transistor Substitution data book about 2SC458
Click to expand...

Thanks! That sub chart helps. I ordered the 2sc2240 based on the info I found on this site regarding replacements for the 2sc458. I was not aware that there was a more suitable replacement than the 2sc2240.

That chart helps because, I do have a bunch of the 2sc945 already. So that would save me from having to wait wait even longer for a reorder.

So, I still don't understand why I found those posts in this forum regarding the basing (more than one post). Maybe just a simple mix up. Maybe an entirely different reason that I am not aware of. Who knows.

Thanks for the information. YD
 
Trannys are in (2sc945) and it sounds a little sharper, and clearer if that means anything. Am I hearing more separation or is just because of less noise?

I understand now why I was confused on how to place the transistors. On one side, the transistors go in like normal. On the other side the trannys are basically a mirror of the first side (preamp board). Sorry it's hard to describe, but in a way, they do go in backwards (sort of).

Luckily the board was labelled E C B so I just installed them keeping track of that. Now I'm just waiting for my caps to arrive so I can breath more solder fumes. YD
 
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Transistor basing for original 2SC458's reading left to right is BCE.

Transistor basing for 2SC2240 reading left to right is ECB.

The advisory posted above is WRONG. Some new-production 2SC458's have the same basing as the 2SC2240, but those new devices are not installed in vintage gear.

2SC945 is NOT suitable for low-noise circuits.

Fred
 
"2SC945 is NOT suitable for low-noise circuits."

I was afraid you were gonna come along and say something like that...:D

I did pay attention to the circuit board with the location of E C B and put the legs of the 2sc945 in the apropriate holes, and unit is working fine, but, it looks like I'll be pulling them. :thumbsdn: I assume that as long as I pay attention to E C B, it will keep me out of trouble (like when installing the 2sc945) when I install the 2sc2240.

What about the data sheets I have posted? To me it looks like they are the same. Is that what you mean by "Some new-production 2SC458's have the same basing as the 2SC2240, but those new devices are not installed in vintage gear"?

The original 2sc458 does look different. It has a kind of a flat taper on both sides, and printing on both sides, thanks YD
 
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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.

* * * * *

Back in the late 1970's, when 2SC458's began to fail, I used the 2SC1775 as a replacement. I chose it because in the spec manual it was called out as a low-noice small-signal device with a bandwidth not dissimilar to the 2SC458, and because the 2SC1775 was used in many machines I encountered -- and the device never seemed to fail.

By the early 1990's, the 2SC2240 had proved itself as a wonderful small-signal, low-noise transistor, again with an acceptable bandwidth, so I began using it as a replacement for the 2SC458.

* * * * *

A brief look at the specs reveals that the 2SC945 is an older-generation small-signal transistor not intended for super low-noise applications. It works fine as a basic, small-signal transistor, and is fine for many applications. I would never stick it in a low-noise circuit.

In transistor selection, like many other aspects of electronics, the devil is in the details.

* * * * *

As of this writing, I have probably replaced about 10,000 2SC458's with better-performing devices.

Fred
 
Fred, thanks for the detailed information. The 2sc2240's arrived today and they are installed. Things are working and sounding fine. YD
 
So, should 2SC458's of any age be replaced anywhere they are found?

I found a few in my 1000X

John
 
Thank you for the update - I found 2 - they looked so odd I checked up on them - particularly here on AK, and found them pretty much regarded as the spawn of the devil himself. I used BC182 as the replacement in my 1000X - they work just fine. The old ones are now in my 'rogues gallery' :D

Thanks again EW :thmbsp:
 
So I'm looking to replace some 2SC458LG s in an Akai GX-635D and have some 2SC1815s here I planned on using, but would I be better off with some 2SC2240s???
 
The 2SC1815L, which is a low noise version of the 2SC1815, is close to the 2SC2240 in regards to noise performances.

Any one of them, including the regular 2SC1815, is better than the 2SC458LG. Try the 2SC1815s you have.
 
The issue here is not so much the noise level of the transistor, but the fact they need to be matched to each other in this situation. You can buy a bag of 100 2SC945s for peanuts and beta match/curve trace them and you will get a better performing GX625 than just putting 10 or 12 so-called lower noise transistors in that you haven't matched.
 
restorer-john said:
The issue here is not so much the noise level of the transistor, but the fact they need to be matched to each other in this situation. You can buy a bag of 100 2SC945s for peanuts and beta match/curve trace them and you will get a better performing GX625 than just putting 10 or 12 so-called lower noise transistors in that you haven't matched.
Click to expand...

I disagree. In the GX-635D, the 2SC458s (7 per channel) are at the input stage of the mic preamp, line preamp, play head preamp, and source/tape preamp. Noise factor is the most important criterion for this particular application. Furthermore, they are in single ended circuit, not in differential stage, and they don't need to be matched.
 
hello: I'm trying to buy some 2SC2240 transistors from Digikey or Mouser, but am not having any success at all with this part number (to replace my 2SC458s)

can anyone recommend an alternate, or, better still the correct Digikey part #?

thanks!
 
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