View Full Version : Help needed - Transistor replacement / substitution


BruceRPA
05-13-2010, 10:10 PM
I am working on a Marantz 2270 for a friend. It cleaned up very nicely, the amplifier sections adjusted perfectly and everything works for the first few minutes until there is a LOT of random noise through the left channel. I have isolated the problem to transistor #H408. The schematic shows that it is a "2SC493 Y or Gr". I searched for a couple of hours and can not find a replacement or a substitute that is not in a TO-3 case. The original is a TO220 case. I am really frustrated that I can not find a simple replacement for this thing. It doesn't look like anything all that unusual, at least to me. I did find an old comment in the archives of another forum about a similar model from our very own Echowars that stated that these transistors are troublesome and should be replaced as complimentary pairs (it's mate is a 2SC1000 Gr or BL). I am all for doing exactly that if only I could find the transistors to do so.

While we are at it, I am also working on a Technics SU-8600 for the same friend with exactly the same symptoms. In this case the trouble has been isolated to TR405, which is a 2SA794Q.

If anyone can point me in the right direction I sure would appreciate it!

KingBubba
05-13-2010, 10:30 PM
Might be of help.

http://www.audiokarma.org/forums/archive/index.php/t-206653.html

goat67
05-14-2010, 07:31 AM
The best I could find for the 2SC493 is this it has a lower ft 863-BU406G at Mouser.
Maybe someone else can verify as a good sub?

BruceRPA
05-14-2010, 12:32 PM
Thanks guys! I read through the thread and picked some good up info. I am not sure about the transistor sub either.

With all the power of this Internet thing, I am surprised that I have not been able to find much at all about the OEM transistors. I will search some more over the weekend but I think that I actually found the end of the Internet last night. :rolleyes: I did find quite a few obviously bad search results that took me into some peculiar territory along the way.

I sure could use some help on this one.

ecluser
05-14-2010, 12:48 PM
H408 can not be a 2SC493, it is probably a 2SA493, in a TO98 body

Replace with any low noise PNP: 2SA970, 2SA872, 2SA992, 2SA1015L, 2SA1048L, 2SA1049, 2SA1084, 2SA1085

Check your pin-out and the pin-out for the replacement transistors.

BruceRPA
05-14-2010, 01:12 PM
H408 can not be a 2SC493, it is probably a 2SA493, in a TO98 body

Replace with any low noise PNP: 2SA970, 2SA872, 2SA992, 2SA1015L, 2SA1048L, 2SA1049, 2SA1084, 2SA1085

Check your pin-out and the pin-out for the replacement transistors.

Well that certainly would explain a lot of things! I am at work now but this weekend I will check the schematic and verify the numbers on the transistor itself. It would not be the first time that I have encountered an error on a schematic - or the schematic reader himself!

ecluser
05-14-2010, 08:27 PM
The schematic says 2SC493 but it is not possible for a NPN to work in this position.

BruceRPA
05-14-2010, 09:54 PM
Bingo! I think you nailed it ecluser! Thank you! :thmbsp:

The schematic definitely does read#H408, "2SC493 Y or Gr" but the transistor itself is marked A493 and it has a "Y" stamped on the top of the case. It is a TO98 case.

It's mate on the PCB is #H406 and the transistor is marked "C1000". The top of the TO98 case is stamped "BL". I Hope this one is correct and the transistor actually is a 2SC1000 BL. Does that make sense to you?

I plan to replace both pairs (both channels). I will look for replacements to order in the morning unless you have a specific recommendation (it is almost 11PM now - and I am tired).

Once again, thank you and everyone else that offered to help. :thmbsp:

donberry
05-14-2010, 10:01 PM
KSD526 is the replacement in the right case

ecluser
05-15-2010, 08:24 AM
The KSD526 is a NPN, 30W power transistor. No place for such a transistor in a preamp...

The 2SC1000BL is frequently used in preamp. It is not really important that the NPNs and the PNPs are the exact complementary pairs in this application. But if you want to do it, just consult the datasheets for the correct mate. For example, the mate for the 2SA970BL is the 2SC2240BL. The 2SA1015L and the 2SA1048L are low noise versions of the 2SA1015 and 2SA1048. In this case, the "L" is not the hFE class.

donberry
05-15-2010, 02:17 PM
he asked for the replacement for a 2SC493 in a T220 case.
The replacement for a 2sc493 is the KSD526

BruceRPA
05-15-2010, 07:06 PM
Actually, I am the one that caused the confusion. I am working on two units at the same time and I mixed up the physical properties of the two transistors that I am looking for. The Technics unit does need a power transistor that is not in a TO3 case. The Marantz needs the small TO98 case for use in the preamp. I am afraid that I asked for the wrong transistor number due to the schematic error (and my not comparing it to the markings on the device) and compounded the problem by asking for the wrong case type. You fine folks stepped up trying to help find what I asked for even though I was way off. Sorry for the confusion. I do appreciate everyones help. :thmbsp:

BruceRPA
06-22-2010, 12:46 PM
AH, the sweet sound of success! :music:

I want to be sure to offer my most sincere thank you to everyone that offered to help. I really do appreciate it. :thmbsp:

The information was spot-on and both the Marantz receiver and the Technics integrated amplifier work great now! My friend is thrilled with the sound and the performance of the Marantz even though the Technics that he had been using for many years is no slouch.

Just as a side note to this story, some may find that how this all came to be may be of interest since we all seem to share some aspect of our interest in music and / or vintage equipment. I will attempt to be brief. I met my new friend just recently while looking through the LPs at a GW store nearby. We struck up a conversation and one thing led to another. As it turns out he makes his living buying and selling Vinyl. After a few more chance encounters with him at the GW store he mentioned that he had an increasingly annoying problem with his system but he had no idea about what to do about it. It had just reached the point of being unbearable. He did know that he couldn't just run down to a store and buy another amplifier (with two phono inputs) that would be close to the quality of his present equipment. I mentioned that I do minor repairs on vintage equipment and offered to take a look and listen. He lives right around the corner from where I work. It only took a minute to determine that he had something more serious than a noisy pot in his Technics amplifier so I offered to loan him a Sansui receiver while I looked at the amp. He then drug out this crusty Marantz that he had in storage for quite a few years.

I think I pretty much covered the rest of the story in the OP so I think that you can take it from here. The Karma that has resulted from this chance encounter has laid the foundation for a new friendship that I am really looking forward to developing - and you fine folks have contributed in no small way! I think that we are very similar in a lot of ways but with different backgrounds. Josh knows more about music and artists than I could ever hope to learn so as we get to know each other and share our experiences we will both get to share in the sweet sounds that the Karma has provided.

So, once again, I want to thank you all for more than just your technical help.