Working on a KA-907- Got Substitutions?

Trnsfmr_Jr

New Member
Working on this real jerk of a Kenwood. Great amp but it suffers from a VERY intermittent problem. I can get it to crop up once every 3-5 hours for 30 seconds. Not even a consistent enough problem that I feel I could find it with freeze spray. Anyways- basically I've narrowed it down to some active component on the "driver board" which is a bit split up on this model. Well to make a long story short I'm about ready for the ol' "shotgun" method of repair at this point. Found some NOS for the FETs but now I am looking for a replacement for 2SA1125 and 2SC2633. Anyone know of a good one? This is for Q15-20 on the so called Power Supply PCB ASS'Y (x00-2010-10). The part I am working on however I assure you is a current mirror and the early stages of the driver. Thanks in advance for anyone's help on this one.
 
Ya already got the black flags and the electrolytics. I get an intermittent distortion on the left channel. On the scope it looks like I'm losing the negative side of my sine wave- something like a missing voltage to a TR or a TR intermittently going bad. I got lucky one time and was able to see it on the plugs that leave the "driver board" and go to the actual drivers and outputs, with the plugs unplugged. So I know it is before the output section. I've also been able to see good signal going in to the driver from the preamp. I just can't get the problem to happen consistently enough to troubleshoot the board that I know it is on. Thanks for the tip about the xpost, Ill do that now.
 
I would take new transistors - no china Fake please!! For example sanken 2SA1859/1859A & 2SC4883/4883A. They do work fine in this amp ( and also in the L-07 M II). And they are fast enough.

Richard
 
I would take new transistors - no china Fake please!! For example sanken 2SA1859/1859A & 2SC4883/4883A. They do work fine in this amp ( and also in the L-07 M II). And they are fast enough.

Richard


Thank You.

Tried these TRs and it seems to have been the culprit. Had it playing for 3 days now and no problems. Found the TRs on digikey.

Thanks again, seriously,

Justin
 
2SA1125 and 2SC2633, complimentary pair, specs on original parts and suggested replacements:

2SA1125
Silicon PNP in TO-220 package with BCE pinout
Vcbo: -150 V
Vceo: -150 V
Vebo: -5 V
Ic: -50 mA
Pd: 1.5 W
hFE: 90-450 (service manual states R or S gain code, so we're looking for 130-330)
fT: 200 MHz​


2SC2633
Silicon NPN in TO-220 package with BCE pinout
Vcbo: 150 V
Vceo: 150 V
Vebo: 5 V
Ic: 50 mA
Pd: 1.5 W
hFE: 90-450 (service manual states R or S gain code, so we're looking for 130-330)
fT: 160 MHz​


KSC2690A and KSA1220A would work well as replacements which are complimentary. TO-126 package, ECB pinout (so just spin 180 degrees).

KSC3503F and KSA1381 would work well, too, but might be a little difficult to find. TO-126 package, ECB pinout (so just spin 180 degrees).

MJE15034 and MJE15035 would work OK, but might not have enough gain for your application. TO-220 package, BCE pinout.
 
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