Soon after I completed my Crack in early 2012 I bought the ebay 6SN7 adapter that some of the early tube rollers were linking to as a decent way to run the 6SN7. Though I received the adapter I never put it to use, staying with the trusty CV4003 I started out with.
A recent project has me now in possession of a few 6SN7s and so I decided to pop in that adapter as see if I liked what I heard. But as some posted back then, I immediately heard the dreaded hum. Recently I came across an American made unit that is, to me, much superior.
This unit uses a small, round, custom pc board into which a ceramic octal socket and the 9 pins are soldered – no messy wires to capacitive couple the AC to the grid. I picked one up and it works beautifully. My Crack was dead silent before and is dead silent now. The adapter is also about ¼†shorter than the Chinese units I’ve tried.
The pc board has two pairs of solder bridging pads on the bottom which allow some configuration changes. Bridge one pad and the 4 pin of the 12AU7 side is connected to the 8 heater pin on the octal with 5 open (pin 9 on the 12AU7 side is connected to the 7 heater pin on the octal). Bridge the other and the 5 pin connects to the 8 on the octal, with 4 open. Of course, you can also bridge both. The adapter comes in three pre-soldered versions but is very easy to resolder to any of the configurations.
The only downside on the Crack (for me) is that there is some space between the socket and the board, exposing the octal connections to the pc board – not good with grandchildren running around the place. It was designed for an amp where the original 9 pin socket lies well beneath the top plate. Since on the Crack it sits above, I filled the space between the socket and pc board with Sugru. One could use electrical tape, silicone, Sugru or any non-conductive material.
The board is made by an outfit that is a Bottlehead competitor in that they produce DIY amplifier kits so I won’t provide a direct link here. If you Google “1217 6SN7 adapter†and look down the results a bit to a link for “amplifier build parts and extras†you will find the link. (Feel free to PM me if you have trouble finding it). Be sure to choose the first version listed as this will match the Crack pin requirement. Do not order the version marked “general†– its pin outs are incorrect for Bottlehead use. They are $24.99 plus shipping – well worth the money IMHO.