Sansui AU-222 smaller transistor replacements

[jd-audio]

Hi Guys,

I have an nice little AU-222 amp. It is working fine and is used as a daily driver.
But I am wondering about the replacement transistors that are present on the amp board.
I have got this amp recapped in the past and also had it serviced/repaired once or twice over the years (due to crackling/popping of the sound), during these processes the smaller transistors on all boards are replaced (I have no further details about the services/repairs).

Instead of the original transistors, the following transistors are on the amp board:
Now BC547C F01 instead of both 2SC871 and 2SC815 (according to the service manual).
Now CTBC557B JC instead of 2SA539 (according to the service manual).

As I do not know anything about transistors, but have a curious mind, I have the following questions:
1. Are the present transistors correct or decent replacements for the original ones?
2. If not, what would be the consequenses (soundwise, durability, etc.)?

-John-

 

[stereofun]

Judged on hfe, speed and Voltage ratings, yes they are good replacements in the sense that they don't fall short. - where it gets a bit murkier and where you really have to understand the circuit is when it comes to current ratings. So the originals 2sc871/815 have a collector current rating of 30mA and 200mA respectively. The replacement is rated at 100mA - which means that you are 100mA short vs the 2sc815.

Before we begin to over-analyze we should consider that current ratings are arbitrary in the sense that an engineer might need say a 50mA current rating to be on the safe side, so the "next step up" from a 30mA, just happens to provide 200mA.

However, there are some indicators to go by for us mortals - A) does the amp sound good and can stay on for hours without developing pops or noise. B) does any of the replacements feel hot to the touch (here you can use a thermoscan device or simply let the amp run for a while, turn it off and check the temp between thumb and index finger). A transistor that is running against its current rating will develop heat, if that is the case we can help you find a better replacement for long term reliability.

For the other transistors just check on alltransistors.com and compare ratings.

 

[quadmatrix82]

If i was restoring a au-222 i'd use ksc1845 or 2sc2240 in place of 2sc871.

For the 2sc815 i'd try to source originals or ksc815

not sure if the substitute you mentioned is the best to replace those components in those areas - others can chime in on that but the above suggestions i made are proven replacements for this amp.

 

[Hyperion]

KSC815 (for 2SC815) and KSA539 (for 2SA539) - both exist ! - this is pretty handy as they are a complementary pair. Always desirable to use rather than a couple of randomly chosen devices which happen to meet the specifications.

KSC815
https://www.mouser.co.uk/ProductDetail/ON-Semiconductor-Fairchild/KSC815YTA?qs=/ha2pyFaduio36%2BTlkxBjeKT3T3Uok114ltqWIk702w=

KSA539
https://www.mouser.co.uk/ProductDetail/ON-Semiconductor-Fairchild/KSA539CYTA?qs=/ha2pyFaduidMWpQ4l/EE%2Bbol6%2BUVM83XSq9P1KSLMs=

@jd-audio - want you to see this^^^

I would be very wary of any 2SC2240 transistors you may be able to buy, as they are likely to be fakes, which is a shame as they were useful devices.

 

[jd-audio]

I am very happy to see that I have got some very informative replies to my post.

@stereofun
Thank you for your clear explaining and for your advise. The transistiors don't heat up and the amp is behaving normally, so I won't take any action for now.

@quadmatrix82
Thank you for your information.

@Hyperion
Now I understand what a complementary pair is (I have investigated a bit after reading your reply), I will use your information if this amp needs service in the future. Thank you.

Have fun
-John-