I originally posted this as a separate thread but am re-posting it here at Slowhand's request.
I have been intrigued by the 2C22/7193 tubes since reading about them in the "Supratek Tube Swappin'" thread, especially the comments from Audiogon member Ecclectique, who described them as "magnificent". I was not, however, interested in totally rewiring my Chenin in order to use them. So, after thinking about it for a while I came up with the idea to make socket adapters for the 7193s, using new tube bases, ceramic tube sockets, ceramic tube caps, and rubber-coated hookup wire.
How did it work out? In short, GREAT! The 7193s are spectacular in both sound and looks (with their cute dual top caps). The gain of the tube is lower than that of the 6SN7, but I had WAY too much gain anyway - I only ran the Chenin on the low gain setting with the 6SN7s, and I had to switch my Gilmore amp to the low gain setting (20dB gain) to get any usable range on the volume control. With the 7193s, I have the Gilmore set to high gain (27dB) and 12 o'clock on the volume dial is about 85-90dB at my chair. The gain switches behind the 6SN7s on the Chenin no longer do anything after this mod, since they only attenuate the second triode of the 6SN7. The following two links have pictures of the completed adapters and the Chenin with the adapters and the 7193 tubes installed.
AdaptersCheninOne minor wiring change needs to be made to the Chenin in order for this to work: the two output leads (one has the big Auricap on it) that connect the 6SN7 tube socket to the output transformer on each channel need to be moved from Anode II (pin 2) to Anode I (pin 5) and from Cathode II (pin 3) to Cathode I (pin 6), respectively, since the 7193 is a single triode tube. This is a very easy job - there is plenty of room in the chassis, even for a ham-fisted guy like me. The reward for this minor change - glorious sound!! The 7193 is a spectacular tube, with airy highs that seem to float into the room, a nice warm midrange, and solid, tight bass. Best of all, the National Union tubes I am using retail for $5.00 and change from AES!!! They are pristine new-in-box JAN tubes, dated June 1943, with all the printing intact. I'm getting sound at least as good as the very best 6SN7s almost for free!! I have RCA and Ken-Rad versions of this tube on order so I can compare the sound, but the NUs are certainly no slouch. They kick the hell out of the RCA Grey Glass VT-231s I was using previously.
If you are still uncertain, how about this fact - you can still use your 6SN7 tubes without moving the wires back! Just remove the 7193s and adapters and plug the 6SN7s right back in! You will only be using one of the triodes in the 6SN7, but that still gives plenty of gain to work with, at least in my system. In fact, I think the 6SN7s sound better this way than with both triodes hooked up. If you don't like the sound, simply move the two wires back to where they were.
Details of the adapter wiring:
Anode of 7193 (top cap) to Anode 1 of 6SN7 socket (pin 5)
Grid of 7193 (top cap) to Grid 1 of 6SN7 socket (pin 4)
Cathode of 7193 (pin 8) to Cathode 1 of 6SN7 socket (pin 6)
Heater 1 of 7193 (pin 2) to Heater 1 of 6SN7 socket (pin 8)
Heater 2 of 7193 (pin 7) to Heater 2 of 6SN7 socket (pin7)
Remember, all pinouts are looking at the bottom of the tubes/sockets, with the index pin detent at the top; the pin numbers increase from 1 to 8 in a clockwise direction. You can obtain data sheets for these and many other tubes online from a variety of sources.
Hints:
Drill holes in the tube base to pass the two top-cap wires through. Be certain to actually test-fit the bases into both of your Chenin's tube sockets and mark where you want to drill the holes - the other tubes might interfere with the top cap wires if you don't put the holes in the right places, plus you probably want to make the placement of the wires symmetrical on both sides, and the Chenin sockets may not both be aligned in the same way - it's always better to measure than to do it twice.
Tin the wire ends that go into the tube base to prevent loose strands from accidentally short-circuiting the adapter. This also allows the wire to form a bond with the entire pin after the pin is heated with the soldering iron.
Make the wires between the tube base and the socket as short as they can be while still allowing you enough room to guide the wires into place and solder them. There is not a lot of room inside the tube base when the sockets are pushed into place inside the base, so you need to arrange them so the socket will fit to the proper depth.
Only three of the pins from the socket are used for this adapter, so I snipped off about 2/3 of the length of the unused soldering tabs and bent them over to prevent them from touching any of the other tabs when the socket is pushed in. I didn't snip them off completely since the pin holders on the other side would then fall off.
I coated the socket tabs and the base pin holes with a high dielectric conformal urethane coating (from a local electronics shop) and let it cure until it was no longer tacky before pushing the sockets into the bases to help prevent any accidental short circuits.
I used a two-part epoxy to seal the sockets to the bases - just coat the base on the inside and push the socket right into it. It is a nice tight fit. I then clamped the two together with a C-clamp for 24 hrs until the epoxy was completely dry.
Re-check the pinouts before you use the adapter, just in case! This can be done by checking continuity with a multimeter.
Materials: I sourced the tube bases, ceramic sockets, and small (1/4") tube caps from The Tube Center in Orlando, Fla. The wire used was Belden rubber coated hookup wire #8899 from Newark Electronics in Palatine, Il.
If you try this, have fun and enjoy the results!
Disclaimer: You do this mod at your own risk as I cannot be certain of the setup of all of your Supratek preamps. I know this mod works for my preamp. Please check your preamp thoroughly and verify the correct pin locations before attempting.
