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I recently completed the end of a long journey, with the satisfaction that an old Pioneer tube receiver is once again playing, and it is the amplifier with the lowest noise of all amps I currently own.
This was almost a lost project as 10 years ago while troubleshooting I removed two of the little black square box six lead Tone Modules. As with every thing I do I made a diagram of where each lead is connected to.
Well somehow the diagram was lost and the original schematic does not provide the module identification lead numbers.
One attempt of mine was to biuld two modules on perf-board, and it failed to work.
I even bypassed the Tone Control section and had the SX-110 playing for a few month's, with the gain scaling affected by the lack of the module in the audio chain.
Then, one day, I found the drawing among old papers and notes. I jumped up and down, pulled the little soapbox modules out of storage and installed them back into the amplifier.
This project has been many many hours of work, I have now the amplifier playing magnificently, yet the Phono and FM sections are still not performing well.
But I can attest to the fact that the 7868 Electro Harmonix tubes are wonderful, the bloom and presence they provide makes this a great amplifier to use as a Stereo Video entertainment piece.
I put my ear right up against the speakers and hear nothing, unless of course I turn up the volume past 3'Oclock and then a slight hum/buzz will leak out, but still, this amp has a great clean and open bottom end.
The only complaint with these old Japanese amps is the large amount of ELNA PIO caps that dry out, along with a substantial amount of small Suzuki tubular wire wound resistors that drift or crack.
All of the Green-Drop coupling caps have been changed in the Audio chain, so my next efforts will be to update the FM section and end with revamping the Phono section.
Anyone needing advice or help with this old tube receiver just send me a mail.
I tend to stay away from old Tube Receivers as they require the most amount of dedication and time to restore.
Hope all of you are well and warming up the tubes for Fall and Winter.
Happy toobing.
Follow Ups:
Hello TimeConstant:
I have an SX-110 which I know nothing about. I did notice some of the tubes get very hot (e.g.can't hold my hand to the top of the housing (don't know the right term)). Wondering if this is normal? I would like to pick your brain a little, but can't seem to get your email. If interested, please email me: umbralimi@gmail.com
Thanks!
Canquest
Thanks very much for the post. I have a Pioneer tube integrated amp, that I will be rebuilding, and It is good to know the possible pitfalls. I also have a Japanese made Lafayette receiver that works and actually sounds good, but I am sure it will need work eventually. The transformers on both units are very high quality.
Dave
A a quick look at a schematic indicates an active EQ RIAA preamp. A distinct possibility for upgrade is the tweaked RCA setup (passive EQ) that I've uploaded MANY times.
Eli D.
Yup, I lost a few sheets of something I once was working on. Kinda turns a project into trash!!!!
I always wanted to hear how a Pioneer tubed setup sounds. Never EVERY got a chance to hear the big brand name tubed offerings.
Enjoy, sounds like a fine project.
charles
I cannot confirm this in writing but I have read that the Output and Power Transformers used in these Pioneer Tube Receivers and Integrated Amplifiers were wound by Hashimoto under contract.
I have found that more than any other factor, high quality output transformers make a real difference in the sound.
Years ago I also restored a Sansui 1000A and the performance of the Pioneer SX-110 reminds me of that super liquid presence the Sansui had.
Currently I am using the SX-110 in my Family Living Room connected to the Stereo OUT of my Plasma TV. Speakers are Focal 706V and the match is pretty good.
The original Loudness capacitors had a very muddy bass, so the new Poly caps really cleaned up the low end. I use the Loudness late night and early morning at low volumes.
One nice feature is the AUX input has a rear level control potentiometer. It helps tame the Digital Sources down to 1970's line levels.
All in all I will find is sad to part with this receiver after so many years or work.
But once I get the Phono Stage and the FM Stereo up to par, it will be looking for a new home.
This is in line for the upcoming winter season project list.
Leonard Cohen's vocals really come through on this receiver.
Sansui definitely used Hashimoto "iron". Therefore, the sonic similarities you observe make sense. Darned tootin that the quality of magnetics has a substantial impact on tubed amp performance.
Eli D.
I have a Pioneer tube integrated amp and the transformers appear to be very high quality. The circuitry is very similar to the Sansui amps that I have seem.
Dave
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