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Old 15th April 2010, 01:24 AM   #1
rwm8088 is offline rwm8088  United States
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Default Sansui 500EA vs. 500A

Hello all. I've got a Sansui 500EA receiver I found on Ebay a little over 2 years ago. It's got a set of 6BM8s (ECL82) in the output section, and every piece of documentation I've found is for the 500A, which uses 7189s. I'm guessing that's because this is a european version (is receives long wave as well as medium wave and FM) and am wondering what other differences there might be between the two models.
I'm re-capping it, and replacing the horribly hissy solid-state phono preamp with a 6H30-based preamp, and hoping the sound improves, as I suspect it will. From what I've read on the 6BM8 tubes, the slightly shrill upper midrange is something I can expect to stay, but I hope not. I'm not too concerned with great fidelity at speaker levels since I use headphones 80% of the time, but am looking to improve what I can. I understand this amp isn't going to compare with the Sansui 1000, and don't expect it to.
This amp has not been easy to work on and lately I've been looking for reasons to just abandon it. It's not in great shape, rust and corrosion all over the chassis, missing fuse holder, cheap Czeck tubes, but it is a neat unit and I have grown attached to it. I stopped listening to vinyl with it because of the phono preamp, and was using it with my Akai M8 reel-to-reel before I realized the M8's SE internal amplifiers sound so much better than the 500EA.
I was wondering what others have experienced with the 500EA (or 500A) and if some of the shrillness is directly related to the type of output tubes. If so I'll probly scrap the whole project, as I don't want to redo the whole output section for a better tube... if I did, I'd probly just go with 6BQ5s. WHen I bought this receiver, I had in mind my old Sansui TR707A, Sansui's first transistorized amp but I realize now that was comparing apples and oranges. But they look nice side-by-side, at least. Any advice, other than 'Scrap it'?
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Old 15th April 2010, 02:06 AM   #2
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A tubed phono stage rates to have better sonics, but there is absolutely no reason to fault SS for poor S/N, in general. FWIW, I'd look into reworking the SS phono section and having druthers between 2 phono preamps. The 2SB51 Sansui used is long since obsolete. However, some PNP BJT types are among the quietest active devices, regardless of technology, available. Maybe you'll get lucky and replacement will be "plug and play".

A schematic can be found here. The topology is voltage amplifier DC coupled to "concertina" phase splitter, which is quite commonly seen.
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Old 15th April 2010, 11:12 AM   #3
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Quote:
Originally Posted by rwm8088 View Post
Hello all. I've got a Sansui 500EA receiver I found on Ebay a little over 2 years ago. It's got a set of 6BM8s (ECL82) in the output section, and every piece of documentation I've found is for the 500A, which uses 7189s. I'm guessing that's because this is a european version (is receives long wave as well as medium wave and FM) and am wondering what other differences there might be between the two models.
I'm re-capping it, and replacing the horribly hissy solid-state phono preamp with a 6H30-based preamp, and hoping the sound improves, as I suspect it will. From what I've read on the 6BM8 tubes, the slightly shrill upper midrange is something I can expect to stay, but I hope not. I'm not too concerned with great fidelity at speaker levels since I use headphones 80% of the time, but am looking to improve what I can. I understand this amp isn't going to compare with the Sansui 1000, and don't expect it to.
This amp has not been easy to work on and lately I've been looking for reasons to just abandon it. It's not in great shape, rust and corrosion all over the chassis, missing fuse holder, cheap Czeck tubes, but it is a neat unit and I have grown attached to it. I stopped listening to vinyl with it because of the phono preamp, and was using it with my Akai M8 reel-to-reel before I realized the M8's SE internal amplifiers sound so much better than the 500EA.
I was wondering what others have experienced with the 500EA (or 500A) and if some of the shrillness is directly related to the type of output tubes. If so I'll probly scrap the whole project, as I don't want to redo the whole output section for a better tube... if I did, I'd probly just go with 6BQ5s. WHen I bought this receiver, I had in mind my old Sansui TR707A, Sansui's first transistorized amp but I realize now that was comparing apples and oranges. But they look nice side-by-side, at least. Any advice, other than 'Scrap it'?
IME all the small and large capacitors in japanese tube gear need replacing.
Only after you have done that, look at anything else.
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Old 16th April 2010, 06:16 AM   #4
rwm8088 is offline rwm8088  United States
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Thanks for the link to the schematic, I fixed the FM MPX unit today and now the FM band works, simple fix, one leaky cap and a bad 6AC8. This receiver has a TON of small Elna and Suzuki oil-filled caps, most of which are bulging out of their plastic sleeves by about 1mm, and the parts list keeps growing. So far I've finished with the output section, the MPX unit, and left off at right channel's tone stack when I started running out of caps of the proper values. Good progress for a day, I guess. The filter caps haven't gone yet, which is good because two of them are huge 200mf 180v cans and I can't find any new ones close to that rating that aren't horribly expensive.
When I bought the amp, I made the wrong assumption that it had the same output section as the 500A, which from all accounts I've read is not a bad amp, just not a great one. Seeing the 6BM8s when I pulled the cover was a disappointment as I've not heard great things about this tube. They might not actually be 6BM8s, the chassis has 6BM8 stamped next to the sockets, but the lettering on the tubes is cryllic, and I can't read russian.
At this point I'm just wondering what to expect when it's finished. The only other Sansui product I have from about the same time is my TR-707, which I can't use as a comparison since it's a couple years newer and SS. I'd like to get someone else's opinion and feedback on this particular model (or one with a similar output setup) so I'll know what else to look for if the shrill mid-highs don't go away after I'm done recapping it.
Oh, I've decided to just go the tube route with the phono stages if the harshness goes away. If not, I'll just leave the phono section as it is, and put it back on the shelf next to the TR-707. Thanks again for the info, guys!
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