Hi, I just bought a Technics SE-A100. Due the age and condition of the amp, I'm having to refurbish and upgrade the amp. Along the way, I have noticed that the two thermistor in the circuit are either missing or a resistor was installed. The thermistor in question is encircled in red. Can anyone tell me what the resistance value should be in order to work with the 1.8k resistor?
Hi mate, as far as I know Technics over compensated in the old design, from memory they decided to replace R153+Th151 with a 470 Ohms resistor. You can measure resistor R153 (1.8k Ohms?) and you need to parallel this with another resistor so the total value is 470 Ohms (640 Ohms comes into mind). However Technics completely left out Th151 in the SE-A5000 (re-run of A100). So yeah you can just leave Th151 out.
Thank you Tocxuden, the right channel Th was populated with a resistor but the left channel was left out. Are there anything else I need to know about the A100. I was removing the voltage transistors and found that two of the transistor length were shorter and did not reach the pc board. I guess they just built up the solder to make the connection. Thank you again for your help.
You're welcome. Yikes, did it look like the transistors were replaced (by someone else?)? I'd think Technics were pretty good back in the days, there shouldn't be any half-ass jobs, especially at this calibre. I still use their rx50 speakers, one of the best made by them. Maybe you'd want to replace the two side panels with real wood, simply stunning.
Nội Quy cho quyền sử dụng tiếng Việt lẫn tiếng Anh. 3. Tiếng Việt có dấu là ngôn ngữ giao dịch chính thức của diễn đàn VNAV trong các hoạt động trực tuyến. Các từ kỹ thuật, thuật ngữ chuyên môn và tên riêng, địa danh được phép giữ nguyên từ gốc bằng tiếng nước ngoài trong trường hợp không có từ tiếng Việt tương đương để diễn đạt. Đối với thành viên là người nước ngoài hoặc người Việt Nam sinh sống ở nước ngoài không sử dụng thành thạo bộ gõ tiếng Việt có thể đăng bài bằng tiếng Việt không dấu (không khuyến khích) hoặc sử dụng tiếng Anh là ngôn ngữ giao dịch thứ 2 trên diễn đàn.
I found more issues with the amp, whoever previously repaired it used to hot an iron and took the eyelets of the pc board. I repaired the run and installed the correct resistor value.
Actually, I feel like an autobody shop. I am disassembling the whole amp to sand away the rust that has corroded the chassis. I have completed the transformers and now I am on the main chassis, top side. This amp was taken to the butcher shop to be repaired. The Meter lamp were replace with what I call a Christmas lights hook up. Lamps were solder across each light holder. Really messy and I fixed that with some LED fuse lights. I got some soft whites, expecting that the bright white will be hard on the eyes. I think the original problem with this machine was you could not adjust the left channel voltage control amp and they started going in and shot gunning it to make it work. They replace all the emitter resistors from the .33 ohms to 1 ohm (why, have no idea). I could not find the toshiba transistors, since the last run was in 2000. There are some chinese made ones floating around, but, I do not want to chance of it being fake. I finally found some SEMI that are suitable replacements, so I am changing the whole enchilada to SEMI. The specs are similar. I found the problem in that the R151 was missing and that R153 was not at 1.8k. The missing R151 made it impossible to adjust. I do not know if they took out themselves or mfg error. It still had solder in the holes, so I suspect they forgot to install it in the factory and when it went over the wave solder, it was filled. Hopefully, that fixes everything and no more magic smoke when I turn on the machine and I can make the adjustment. I will let you know how it sounds once the project is completed. I am hoping to use it in conjunction with a Trio KA-9900 as my preamp and Duntech speakers. They are really nice sounding speakers. The mids are so smooth, instrument placement is great and the soundstage extends beyond the speakers.
Good call on the transistors, you do not want to buy anything related to CN if you want your system to sound as it intended. RE are generally there for bias stabilisation and they are responsible for the gain (G=RL/RE) so maybe someone wanted to adjust/reduce the gain and increase bias stabilisation. Looks like you're going all out with this project, very brave and some nice gears you got there. Don't forget to us know how it sounds once you're done.
I will try and keep updated on my journey. I have to admit this is the first time I ever taken a project like this. I also have a Sansui X1 I need to get too after this. The Left channel is out and it down to the left amp, but nothing obvious. The gain in the technics must have been shot with an increase RE, reducing the G.
