M4 output transistors

[Komodo]

I've seen the 2SC2460 / 2SA1050 pairs replacement recommendation of MJ21193G / MJ21194G.

Also dug up this post:
http://audiokarma.org/forums/index.php?threads/yamaha-m4-maintenance-notes.412844/

Where he states: "Don't try to replace with standard power transistors with Fc=4MHz because it won't work (oscillates). What I used instead was the pair 2SC5242+2SA1962, they have better breakdown voltage and current. Fc is only (!) 30MHz but it works. The case is not the same (TO3 x TO3P), so you will need a piece of metal to adapt, making contact between collector (soldered) and the screw."

Does anyone have opinions on this?

 

[clinic-audio]

You can easely make adaptation to use perfect sub for :
2SA1050 = 2SA1301
2SC2460 = 2SC3280

They are not in TO3 but TO3-PL (mica insulator different and 1 fixing screw in center )

 

[avionic]

MJ21193G/94G will do the job just fine. I've never had any issues with oscillation.

 

[Komodo]

I have complete faith in the 93/94 pairs as has been recommended. In the interest of curiosity, would an adapter plate be ideally copper sheet in the same size as the TO3-PL body, with an extension in the middle to solder the collector leg? Then the other two would be bent 90 degree to insert? Mica would still go under the transistor adapter, but not under the extension? I've never seen a picture or illustration of this and trying to picture it.

 

[avionic]

Mica would still go under the transistor adapter, but not under the extension?

Mica goes under the transistor.

 

[avionic]

BTW..A little trivia. TO-3 Transistor sockets were designed with round transistor leads in mind. .

 

[Komodo]

BTW..A little trivia. TO-3 Transistor sockets were designed with round transistor leads in mind. .

Point well taken!

 

[Komodo]

OK, one follow up question / scenario:
Right channel is good with all original transistors.
Left channel, original 2SA1050 pair are good, but you were replacing bad 2SC2460 pair - and have the choice of either the new MJ21194G or a known good vintage Toshiba 2SC2461: http://html.alldatasheet.com/html-pdf/108554/TOSHIBA/2SC2461A/596/2/2SC2461A.html

Would you:
A. Replace all transistors in the left channel with the MJ21193G/94G pairs
B. Use MJ21194G / 2SA1050
C. Use 2SC2461 / 2SA1050

 

[avionic]

A. Replace all transistors in the left channel with the MJ21193G/94G pairs

Don't mix different pairs.

 

[tmsears]

Just to throw out my 2 cents, I screwed up my M4 a few months back by letting my meter probe slip while checking voltages... Took out the right channel's 1050s. I went ahead and replaced all outputs on both channels (not necessary) with the 93G/94G pairs. No oscillations, no problems. Sounds just as good as it did before I blew it up.

 

[Komodo]

After an exhaustive search I may have found a parts supplier in Japan who has stock of original Toshiba 2460 \1050 pairs. Are people sitting on stock piles of these or do you think there is interest in some group buy?
I fully understand the depth of counterfeiting and I’m going to great lengths to verify authenticity.

 

[OMGCat!]

You really never know. You'll find stocks of NOS stuff on buyouts/cleanouts sometimes or in repair shops that used to do warranty work but there are also about tons and tons of counterfeit operations out there.

 

[DEAFASABAT]

BTW..A little trivia. TO-3 Transistor sockets were designed with round transistor leads in mind. .

TO-1's? I have one in a monster heat sink, came out of a Nike Hercules system power supply. Seems pretty beefy compared to a TO-3. Stud mount, IIRC