Transistor Replacement 2N5551

[benproiii]

I am building a DX Blame MKII Supercharged and I was wondering If it was a big deal to replace some of the transistors with the types I have on hand.


With these:

Small Signal:
2N5551 = KSC1845FTA
2N5401 = KSA992FTA

VAS Transistor:
MJ15032 = KSC3503

Driver Transistors:
MJ15032 = KSC2690A
MJ15033 = KSC1220A

Output Transistors:
MJL4281A = 2SC5200
MJL4302A = 2SA1943

VBE Multiplier:
BD139 = KSC2690A

[AndrewT]

The 992/1845 has higher voltage and higher hFE and lower current ratings.
I don't have 3503 data.
The 1220/2690 have lower current and lower SOA ratings. Don't use them with 4ohm speakers unless your reduce the Rail voltage significantly.
The 1943/5200 have the same problems as the 1220/2690. Don't use them for 4ohm speakers.
6ohms speaker might be gentle enough, but I'd recommend usage only with 8ohm or higher impedance speakers.

[Tekko]

As Carlos would say: do NOT change anything!!! Use what is stated in the schematic or come up with a design of your own, using the transistors you have.

[jaycee]

It should work well. You may have to adjust the compensation but I don't think so.

[CBS240]

IMO a good design should be able to work with similar transistors or rather ones with the similar characteristics in play. I see no reason why one couldn't use this circuit with the transistors they already have lying around. The IPS diff bias is about 2.3mA per leg so KSC1845/KSA992 would suffice here. Perhaps adjusting R5/R6 & R8/R9 to reflect the change in beta and %difference of re'. It may be possible to squeeze more GBW out of the IPS with higher Hfe and lower capacitance so C13 might be adjusted as well. KSA2690A should be a good replacement for the VAS as 160Vceo should suffice but it would need heatsinked at 7mA * 60V=420mA. They do not have metal tabs but rather solid plastic TO-126. (I have some lying around too.) I'm not so sure they would work as well for the driving stage since Hfe drops out above 600mA vs >1A for the MJE15032. The MJL4281A appears to have slightly bigger SOA and larger Cob than 2SC5200. Other than the higher Vceo, which makes no difference here, they look fairly similar. 60V/4R=15A or 7.5A per device. The beta of the output devices drop out at about 5A. A 4R speaker is assumed to present at some point an even lower impedance drawing more current and at less current gain the drivers would be under lots of stress, not to mention the added distotion. I would recomend at least 1 more pair of outputs for 4R duty.