A little while back I helped a friend get an old Dual turntable working. He found it at a local Goodwill and thought it would be fun to listen to some old Fred Astaire albums, but was having problems getting it to work. The TT seemed to work OK, it just wasn't outputting any sound. I found several problems with it -- an incorrectly-wired cartridge, the stylus was wrecked, and (most importantly) he had NO phono preamp. I found an inexpensive 5534-based preamp and a replacement stylus and checked the setup out with one of my old Windam Hill sampler albums. Even though the electronics were so-so (and I was listening on so-so headphones), it sounded so good that I decided to revive a lot of my old audio gear. I have an SAE MK3-CM power amp that needed some work and a JFET preamp I designed/built back in the '70s that looked like a good starting point.
Unfortunately, the preamp is dead (and I've lost my schematics for it) so I moved on to the SAE. It hadn't been used since the 80's so I figured the electrolytics were in rough shape. So they got replaced. It was "fun" disassembling the amp, because the previous owner had done some ill-advised mods like soldering all the connectors on the front-end PCB. So as it was, it was impossible to remove the PCBs & replace the electrolytics. I ended up cutting the wires and later devised a replacement connector system with some mini bana plugs/jacks. I also replaced the old RCA phono plugs with gold-plated ones. The old ones were pretty tarnished. I'm fortunate because I also have the original owner's manual AND service manual for it.
I have all the stuff necessary to de-solder parts on PCBs so swapping out the electrolytics wasn't all that difficult. While I was at it, I added 1uf poly caps across all the electrolytics. There was sufficient room to do it, so what the heck.
This last week I reassembled the amp and today I powered it up for the first time in about three decades. Carefully. I have a dual 0-40V lab supply so I could monitor the supply current. Pulled the fuses off one side, powered up the other & vice-versa. No problems, at least nothing obvious. The output voltage offset wasn't all that great, but the amp WAS running at reduced supply voltages. +/-40 vs. the normal +/- 75V. Anyway, after finding no really obvious problems I powered it up with its own power supply and it works just fine. Output offset voltage was in the tens of mV range. The 1KHz sine and square wave looked OK. So far, so good. On the bench w/o a load anyway. That's next.
I also had to use some contact cleaner on the speed-control pots in my Technics SL-120 Mk1 turntable. That seemed to address the speed problem. I have an old Adcom high-output MC cartridge (mounted on an Infinity Black Widow tone arm) that probably will need to be replaced, and designed+built an OPA1656-based preamp to replace my ancient (and dead) preamp. I tested the preamp (and turntable/cartridge) using the audio input on my laptop but eventually want a standalone system.
It will be fun to listen to all my old vinyl again.
Unfortunately, the preamp is dead (and I've lost my schematics for it) so I moved on to the SAE. It hadn't been used since the 80's so I figured the electrolytics were in rough shape. So they got replaced. It was "fun" disassembling the amp, because the previous owner had done some ill-advised mods like soldering all the connectors on the front-end PCB. So as it was, it was impossible to remove the PCBs & replace the electrolytics. I ended up cutting the wires and later devised a replacement connector system with some mini bana plugs/jacks. I also replaced the old RCA phono plugs with gold-plated ones. The old ones were pretty tarnished. I'm fortunate because I also have the original owner's manual AND service manual for it.
I have all the stuff necessary to de-solder parts on PCBs so swapping out the electrolytics wasn't all that difficult. While I was at it, I added 1uf poly caps across all the electrolytics. There was sufficient room to do it, so what the heck.
This last week I reassembled the amp and today I powered it up for the first time in about three decades. Carefully. I have a dual 0-40V lab supply so I could monitor the supply current. Pulled the fuses off one side, powered up the other & vice-versa. No problems, at least nothing obvious. The output voltage offset wasn't all that great, but the amp WAS running at reduced supply voltages. +/-40 vs. the normal +/- 75V. Anyway, after finding no really obvious problems I powered it up with its own power supply and it works just fine. Output offset voltage was in the tens of mV range. The 1KHz sine and square wave looked OK. So far, so good. On the bench w/o a load anyway. That's next.
I also had to use some contact cleaner on the speed-control pots in my Technics SL-120 Mk1 turntable. That seemed to address the speed problem. I have an old Adcom high-output MC cartridge (mounted on an Infinity Black Widow tone arm) that probably will need to be replaced, and designed+built an OPA1656-based preamp to replace my ancient (and dead) preamp. I tested the preamp (and turntable/cartridge) using the audio input on my laptop but eventually want a standalone system.
It will be fun to listen to all my old vinyl again.
