Replacement output transistors for 2SA747 and 2SC116 - Yamaha A-1

Jump to Latest
C

cb1

Member
Joined 2014
#1
Need to replace a pair of OT’s on a Yamaha A-1.

Have a couple of recommendations but can anyone say which transistor pair is best suited OR has worked well in this particular amp (or both, of course!)

Would like to place an order today if possible, so all replies much appreciated.

Existing:
2SC1116/2SA747 140V, Ic=10A, Ib=4A, Pc=100W, Ft=15MHz

Possible replacements?:
MJ15022/15023 200V, Ic=16A, Ib=5A, Pd=250W, Ft=7MHz, mouser 23/1
MJ15024/15025 250V, Ic=16A, Ib=5A, Pd=250W, Ft=7MHz mouser 31/575
MJ21193/MJ21194 250V, Ic=16A, Ib=5A, Pd=250W, Ft=7MHz mouser 1176/737

Is lower Ft significant?
And should both channels be replaced whilst repairing the faulty pair?
 
#4
Also, in terms of pairing the two transistors.. if I managed to get an original 2SA747 from Yamaha and then had to use it with the substitute 2SC2461B.. would that likely be better a 'better' pairing than one of the MJ pairings for this particular amp? (It's direct DC coupled and apparently a bit fussy..)
 
#5
If I was doing it , I'd rely on yamaha's substitutes, but I'd always replace them as a channel pair at least (if not both sides)


(I'm not sure if Yamaha sell semi parts to private individuals, I've just got a trade account with them and was just offering the info - from the horses mouth as it were.)
 
#10
Thanks for the links.
Both sellers have very good approval ratings, but one hears so much about 'fakes' etc..

which then drives one towards MJ series from the few main distributors.. Decisions, decisions.,
Ever heard of people being especially happy with MJ21193 being used as replacements?
 
#11
Nikko and littlediode are both ok (I use them), and if you ever did get fakes from them they would refund.

I've only ever got one fake semi from one of them (cold welded/pressed new legs , so perhaps not exactly fake but recovered and relegged) - but I spotted it and I got a refund easily enough.
It's not in their interests to sell fakes
 
#12
cb1 said:
Need to replace a pair of OT’s on a Yamaha A-1.

Have a couple of recommendations but can anyone say which transistor pair is best suited OR has worked well in this particular amp (or both, of course!)

Would like to place an order today if possible, so all replies much appreciated.

Existing:
2SC1116/2SA747 140V, Ic=10A, Ib=4A, Pc=100W, Ft=15MHz
Click to expand...

Ft is around 15 MHz for the 747
sometimes the PNP can be faster.
Think the 1116 is slower around 5 MHz

Sounds very similar to the MJ15015 / MJ15016

where the pnp is around 15 to 18 MHz
and the npn around 5 to 6 MHz
 
#14
Thanks White Dragon.
Because I’m new to this I have to ask whether the specs that you’ve quoted translate into these OT’s working well in this amp? Possibly even better than the originals, or should I try to replace with refurb / items that aren’t from the big distributors?
Thanks again.
 
#15
Don’t use MJ15015/6 - the gain is VERY low on the NPN. Can be decent on the PNP but the spread is all over the map. They *are* an upgraded epitaxial 2N3055, and you can’t polish a turd. If you don’t get original types *from Yamaha* use the MJ21193/4. Obsolete types on E-bay are almost always fake, especially popular Japanese types like Toshiba and Sanken. From surplus dealers, it’s 50/50, but they almost *never* have anything other than old 60 and 80 volt 2N types.
 
#16
Thanks Wg-ski, that’s exactly the sort of informative advice that is so helpful.
MJ21193/4 seems to get recommended most.
With a full set of them in the A-1... can I ask how one might expect the sound quality to change compared to the originals?
 
#17
You probably won’t even notice a difference. Gain linearity is actually pretty decent up to about 8 amps on the MJ2119x. And it is far more important to use high speed flat gain drivers than outputs. Which is why you never skimp on driver transistors (NO TIPs!!!).
 
You must log in or register to reply here.
Top Bottom