Obsolete Transistor Substitution

ZeroG

ZeroG

Super Member
Could use a little help with finding the correct sub for the differential pairs 2SA722 T or U for the amp section of my Marantz 2265.

The NTE has the correct pin-out, the Fairchild does not. Consensus here is that NTE products are last-resort. Are there any other brands to check?

Here are some data sheets I've found, but I could use a little help with determining what's a good or close match.

Thanks!
 

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KSA992 Fairchild correct pin-out. Better and cheaper than original. Mouser.com
Also 2SA970 if you can find them - but I have read a lot of fakes out there. Good luck.
 
As far as I can tell (looking at fairchilds web site), the first letter (P,F,or E) would be Hfe range - all the wants in stock were F which is 300 to 600 hfe. The TA or BU refer to "bulk" or "ammo" packaging for shipping. So expect FBU is the preferred suffix.
 
ZeroG said:
Could use a little help with finding the correct sub for the differential pairs 2SA722 T or U for the amp section of my Marantz 2265.
Click to expand...
I assume you mean the 2SA733. Fairchild has the KSA733C, which is a center-collector part just like the original. The highest gain code available, 'L' (350~700), can be had only in the reel tape packaging. Not a big deal, just have to learn how to work the leads out of the tape without bending them too badly. The full Mouser part number is 512-KSA733CLTA.

The next highest gain code for a center-collector part, 'G' (200~400), is also only available in tape.
 
Differential pair in the schematic are 2SA722 T or U. 2SA733 is complement to 2sc945 general purpose transistors. IMO they would work, but ksa992 would work much better.
 
SB Marantz said:
Why is that?
Click to expand...

Why is What? KSA992 has higher breakdown voltage, lower noise, higher gain. It's the closest available replacement for 2sa992 and 2sa970 spec wise and performance wise. Basing is the same. There are probably a lot of other possibilities. This one seems to be one of the more popular, and works for me.
 
I never used that ksa992 and i am sure that it is treu what you are telling about the spec's but i do not think that the circuit is going to ''gain'' anything from it.

A-722 55V-0,05A-0,15W cutoff 250Mhz
A-733 60V-0,1A - 0,25W cutoff 180Mhz

A-970 120V-0,1A-0,3W-cutoff 100Mhz (a very good low noise Tr)

What more do you want i wonder?
 
I think that sregor's first intention was to correct this information:

SB Marantz said:
2sa 970 / 1815 / 945 wil do just fine.
Click to expand...

because the 2sa1815 is a low voltage (Vceo -12V) HF transistor and 2sa945 doesn't exist. What do exist is the 2sc945, which his a NPN and is not appropriate for the differential stage in the Marantz 2265.

The 2sa733 (the complement of the 2sc945) is not a bad transistor but the KSA992 (or 2SA992, which is the same) has less noise and is another option to the 2SA970, which is not available everywhere.
 
Perhaps I shouldn't have said "much better" the 2sa733 is a fine transistor and would work. I see it used all the time, especially as a current limiter (as in the 2265) and in power supplies and other circuits. I just never see it used for amplifier input stages (I've seen 2sa640, 2sa722, 2sa750, 2sa872, 2sa970, 2sa798, 2sa922, but not 2sa733, so I presumed the others were preferred. (I also assumed that the 1815 and 945 were 2sc typos.) Notice I started with IMO, which means I'm not necessarily correct.
 
Thanks, guys!

Geez, I love this site! Amazing, the degree of expertise that can come forth.

I'll order the KSA992FBU, but I get it that the KSA733 would be fine as well.

I've recapped the main filters, the P800, the tone board, and the phono board, and next would be the P700 boards. So now I can get the differential trannies and replace those at the same time.

This 2265 (as is) is an impressive-sounding unit, and I'm really looking forward to listening to it after a full re-cap.
 
Sorry for my confusion...I did not get out the schematics for the unit, and I am unfamiliar with the 2SA722. Yes, the KSA733 would work well, but as sregor suggests I have not seen it used in a differential mode...although I see no reason why it would not work well as a differential pair tranny. Still, in that application, I'd go for the KSA992 as others have suggested.
 
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