Trio KR-9600 DC Offset Voltage - 2SC1345 Equivalents ??

I recently acquired a Trio KR-9600 receiver in very good condition (bought it on a well known auction site). Upon checking it out I found that the output DC offset was approx 120mV on one channel and 130mV on the other. The KR-9600 does not have adjustment pots for offset, so the only way of reducing it is to replace the differential amplifier transistors.

I discussed this with the seller and he has managed to find a UK source for the original 2SC1345 transistors, but there are only 6 available at a cost of £2 each (approx $4 each). Now the chances of getting two reasonably matched pairs from only 6 transistors is extremely remote, so I am very reluctant to ask him to get them for me (he agreed to pay for the cost of parts to bring the receiver up to spec if I would fit them).

I can get Zetex ZTX694B alternatives (mentioned by EchoWars in other threads) for £0.71 each ($1.40), but would have to buy quite a few (25??) to be able to get the two matched pairs I require. While looking for alternatives I came across the On-Semi BC550C, which is a low noise transistor with very similar specs to the original 2SC1345 (the Vc-e voltage rating is 45V instead of 50V but I don't think this will be a problem in the 9600). The cost of the BC550C is only £0.04 each for a quantity of 25, or £0.02 each for 100, so I could buy lots of them in order to get closely matched pairs.

The data sheets for the 2SC1345, BC550C and ZTX694B are attached below. Opinions please regarding the use of the BC550C as a replacement for the 2SC1345. :scratch2:

Thanks,
Richard B.

The thing I like about the ZTX694B is that I can easily find units with gains in the 1100 to 1500 range. But anything over 500 will be cool. The BC550C will be fine (but, like the Zetex transistor, the pinout is different from the original 2SC1345, which is BCE, and the Zetex and On-Semi is EBC, so pay attention!)

EW, thanks for the swift reply. I'll get some of the BC550C on order - and I'll be real careful with the pin-out when I fit them.

I'm also planning on replacing the back to back polarized tantalum input coupling caps on the amplifier boards with film caps. The original tantalums are 2.2uF, so being in series I guess I can replace them with a 1uF polyester film type.

There are a couple of dead bulbs. One is for the "aux" function indicator, which looks from the service manual to be an 8V 50mA type. The second dead bulb is the illumination for one of the power meters - I can't seem to find it in the service manual, any idea what it's rating and physical size is ??

Thanks again,
Richard B.

Use a 1.2µf or 1.5µf to replace the back-to-back tantalums. At 1µf, low cut-off is about 12Hz...too high. 1.5µf puts it at about 8Hz (usual goal is under 10Hz).

The tuner display lamps and power meters are 8V 250mA (or 300mA...same thing). Dwojo has 'em: http://www.home.earthlink.net/~dwojo/index.html

These are what you'll use: http://www.home.earthlink.net/image...pictures/8v_250ma_wedge_10.jpg&target=tlx_new

Edit: Now that I think about it, I'm not so sure about the power meters. You'll have to pull it out and see what it is.

2nd edit: In my own 9600, I thought the display was too bright with the 8V 250mA lamps. I got some #192 lamps (13.3V 330mA), and at 8V they are perfect...just a tad dimmer than the stock lamps, and you might be able to find them in the UK.