Hello, I have been working on a Lafayette LR-500T receiver for some time now. Date am almost full recap, I still have some minor white noise even if I turn volume to zero. On schematic there are 4 transistors of CS1308 and 2 CS1306, on the main amp board. I tried hard but can’t find any info for the two kinds. I am really curious on what it is. Thanks, Frank
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peteCWA
Active Member
I have no idea why you would want to do a full capacitor replacement. In most cases, it's not necessary and can introduce other problems during replacement.
CS1306 (NPN) and CS1308 (PNP) transistors are drivers for the 2SD92's in each channel.
The additional CS1308 in each channel helps to set the idling current and bias voltage.
Replacement for CS1306 - SE8010
Replacement for CS1308 - 2N4354, 2N4356, 2SB324
On the main amp board, the 2SB33 are germanium transistors. Germanium transistors have a history as they age, to develop material creep at the pn junction when current is passed through the junction. Don't remember if the "CS" transistors are germanium. This "creep" can generate noise. Likewise, some aging carbon resistors can also develop noise when current is passed through them.
On the main amp board, several of the transistors are always conducting, even with zero volume, since idling current for the driver and final transistors is set to 20 ma DC with no signal applied (zero volume).
The service manual for the LR-500/500T has, besides the typical service related information, also trouble-shooting hints and various service related addenda. The LR-500TA receiver design was a huge improvement in design and performance.
However, in this design series, my favorite has always been the LR-1000TA and LR-1000B for performance and reliability.
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wow, thank you for the info. For the CS1306/SE8010, can I replace it with 2N2219A? or any other modern sil transistor?
I got this receiver in non working status. One channel totally out and it was blowing fuse. After recap all the caps, one channel still out. Turns out the Q401 (2SB348, a ge transistor) went bad. I put in a 2SB346 and both channels worked. However, there was quite some big noise on one channel and it usually went quieter after 5 min. Upon closer check, someone put a HEP51 sil transistor in Q501 to replace ge 2SB33. I replaced it with AC128 and noise went down big time but still some. The last thing I can think of is the CS1306/CS1308. But I could not find any info until your response! Thank you!
I got this receiver in non working status. One channel totally out and it was blowing fuse. After recap all the caps, one channel still out. Turns out the Q401 (2SB348, a ge transistor) went bad. I put in a 2SB346 and both channels worked. However, there was quite some big noise on one channel and it usually went quieter after 5 min. Upon closer check, someone put a HEP51 sil transistor in Q501 to replace ge 2SB33. I replaced it with AC128 and noise went down big time but still some. The last thing I can think of is the CS1306/CS1308. But I could not find any info until your response! Thank you!