Cyrus One - problem with new 2SC1775/2SA872

[lightning999]

Hello,

I am currently refurbishing a Cyrus One that suffered a lot of rust/corrosion damage.

I have purchased 2SC1775 and 2SA872 transistors from several places (imported from the USA to UK, just noticed www.elclondon.co.uk sell them for the same price I imported them).

I received the first lot, 25 of each, from one company. Before fitting them I decided to test them quickly on my multimeter, comparing with the original devices I took out (well, the ones that had legs left on them). The original ones gave hFE readings within the specs in the datasheet (2SA872 ~440 and 2SC1775 ~580). The new 2SA872s gave similar readings. The 2SC1775, however, gave hFE readings of 80-280 (datasheet specifies 400-1200). I contacted the company and they refunded the money for these devices stating to not return them (this made me wonder a bit...).

I ordered some more from MCM (30 of each, might build some monoblocks based on the cyrus one someday), these have arrived. Inspecting the devices, 7 of the 2SA872 look the same as the original hitachi devices, the rest look different (with off centre marking on devices etc.) All of the devices, apart from the 7 2SA872s that look alright (and measure around 440 like the originals), have hFE measurements of ~200.

I don't just want to solder these in and end up with a Cyrus One that, either just doesn't work, or sounds rubbish!

Can anyone advise?


Thanks!

[Leolabs]

D and E give different hFE readings.

[lightning999]

yes, for the 2sc1775, E gives 400 to 800, F gives 600 to 1200 and for 2sa872 D gives 250 to 500 and E gives 600 to 1200. So measuring around 200 for both devices is bad I take it...with the originals testing fine, and 7 (out of 60...) of the ones I bought testing fine I presume it's not me testing them badly...

[lightning999]

whoops, the 2sa872 D is 250 to 500 and E should be 400 to 800 hFE (not 600 to 1200....)

[Aleko]

Hi,

I need 2 matched pairs 2SA872 and 2SC1775 for the input stage of my Mission Cambridge amplifier.
The same experience as yours: I bought these and soldered them on the board .
The offset at the output went to 0.2 , 0.5 , 0.8 V dpending on the transisors I used .

Or is that the complementary pairs of driver transisotrs 2SB646 and 2SD666 need to be matched too ?
There are 5 pairs of each or 10 transistors in total.

Total: 14 transistors .

The originals should have been made by ST Electronics .

I am looking to buy them.

Best regards,
Aleko Markov