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Old 21st April 2013, 05:10 PM   #101
jaycee is offline jaycee  United Kingdom
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Do not buy from eBay. You will get fake junk that is really MJ2955/2N3055 - or worse.

I would buy MJ21193/4 as replacements. These are good, solid parts that while not quite as good as the originals, should perform well.

edit: I wouldn't bother with matching. Modern transistors are quite close in batches anyway. I doubt the original amp had matched sets.

Last edited by jaycee; 21st April 2013 at 05:14 PM.
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Old 21st April 2013, 05:15 PM   #102
Mooly is offline Mooly  United Kingdom
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Quote:
Originally Posted by gde3 View Post
I tried to follow instructions, I'm not shure if I had to remove Q11 or not. Secondly I didn't understand where to measure L1.
About the output transistors none is original so I will start with two motorola 2N6030 since they seem in better condition.
One more question how do I measure if the transistors are working right?
You apply a short (piece of wire) to connect the parts of the circuit I illustrated together. Leave Q11 and D6 in place.

Output transistors that have failed will (95% of the time) read short circuit between collector and emitter.

You need one good device of each (NPN and PNP) fitted correctly to do an initial test.

The 2N3442 (npn) and 2SA679 (pnp) are worth trying as the initial test. The npn device is the top one of the pair and the pnp the bottom. Arrow go out for npn and "in" for pnp.

L1 is the main speaker output of the amp. The junction of all the 0.5 ohm emitter resistors.

(and I wouldn't by any semiconductors off ebay. Buy guaranteed parts of known provenance from major recognised suppliers)
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Old 21st April 2013, 05:32 PM   #103
rsavas is offline rsavas  Canada
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Agree with all the above. Gotta like international Pioneer classic restoration :-)
BTW I did no matching either for my change out on the SX-950.
Could be as simple as using the diode tester and sort out based on vbe drop, crude useful?
I know you really want to match at more bias but like I said crude.
May get a discount on buying 10 of each, since you need 6 pairs as it is.
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Old 21st April 2013, 06:09 PM   #104
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Quote:
Originally Posted by Mooly View Post
You apply a short (piece of wire) to connect the parts of the circuit I illustrated together. Leave Q11 and D6 in place.

Output transistors that have failed will (95% of the time) read short circuit between collector and emitter.

You need one good device of each (NPN and PNP) fitted correctly to do an initial test.

The 2N3442 (npn) and 2SA679 (pnp) are worth trying as the initial test. The npn device is the top one of the pair and the pnp the bottom. Arrow go out for npn and "in" for pnp.

L1 is the main speaker output of the amp. The junction of all the 0.5 ohm emitter resistors.

(and I wouldn't by any semiconductors off ebay. Buy guaranteed parts of known provenance from major recognised suppliers)
I tested those two transistors, the voltage at L1 is 34V (I connected the multimeter to pin 13,14 am I right?).
Do I need to test something else or I just repeat this operation for all pair of transistors?
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Old 21st April 2013, 06:50 PM   #105
Mooly is offline Mooly  United Kingdom
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Quote:
Originally Posted by gde3 View Post
I tested those two transistors, the voltage at L1 is 34V (I connected the multimeter to pin 13,14 am I right?).
Do I need to test something else or I just repeat this operation for all pair of transistors?
Yes, the meter goes between pins 13 and 14.

34 volts indicates a problem. This is where fault finding begins.

You need to be sure by measurement that pins 14 and 2 really are connected to ground. You also need to measure and confirm the supply voltages on pins 4 and 7 and pins 3 and 6.

If you are not 100% sure that the output transistors are OK then check another pair (to make sure they are not obviously short) and try those. Be absolutely sure you have them in the correct location and correctly connected.
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Old 21st April 2013, 07:47 PM   #106
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new test 2.235V at L1, is it right?
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Old 21st April 2013, 07:55 PM   #107
jaycee is offline jaycee  United Kingdom
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No. It should be much lower, ideally zero but practically under 100mV.
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Old 21st April 2013, 08:43 PM   #108
rsavas is offline rsavas  Canada
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Try adjusting the offset pot, VR1 to see if you can get the DC offset V as close to 0V, below 100mV is fine probably okay.
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Old 21st April 2013, 09:04 PM   #109
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Only two pair of transistors are working right, I got 80mv and 5 mv out of sanken 2SC1116 and motorola 2N 6030.
So I should definately order some new transistors, I will opt for MJ21193/4 as suggested. I will order from mouser or digikey so I would like to buy as many parts as possible to pay the custom fees only one time (€10+21%VAT)

- Should I substitute the two toshiba 2SC783 and 2SA483? If so what could fit?
- I also would like to change Q11, 2SC281VL

Last edited by gde3; 21st April 2013 at 09:07 PM.
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Old 21st April 2013, 09:20 PM   #110
rsavas is offline rsavas  Canada
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Quote:
I got 80mv and 5 mv out of sanken 2SC1116 and motorola 2N 6030.
this is for 1 or 2 channels tested?
Quote:
two toshiba 2SC783 and 2SA483?
Leave alone unless broken!!
Quote:
I also would like to change Q11, 2SC281VL
Why? Same as above.
Where are you located? I was thinking Italy?
If in Europe may want to try Farnell/Newark/Element14, got some specials going on last time I looked.
Digi-Key & Mouser have free shipping if order is over $200USD
Suggest to replace all the ecaps, bias/offset pots, output transistors(TO-3) /mica insulators,compound and that is it, unless there are other problems.

Last edited by rsavas; 21st April 2013 at 09:46 PM.
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