A better 6SN7 adapter

[btrancho]

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.

[Natural Sound]

How do you like the 6SN7 compared to the 12AU7 (CV4003)?

I punched out the hole and mounted an octal socket for the 6SN7 from the beginning. Later I bought an adapter to go back to the 12AU7 (the opposite of what you did.) After about a month of tube rolling the adapter came out and a 6SN7 has been in ever since. 

[btrancho]

I'm only four or five sessions into the 6SN7 (a JAN CHS 6SN7GT VT-231) and so far I am really liking what I hear.  I'm going through some of my standard albums for critical listening and I'm perceiving a bit more overall clarity and punch.  Coming from the CV4003 that isn't really surprising as it is a little laid back and I'd liked that, especially for jazz.  I'll need a couple of weeks to decide but since it's just the adapter and I have no plans to modify the Crack, it will be easy to switch back at that point for comparison.

BTW, I acquired a Shuguang Black Treasures CV-181 from a friend who bought a matched pair from Psvane a while back for a silly sum and then proceeded to drop one while installing them for the first time.  This one sat in a drawer for over a year and he gave it to me as it was useless to him as a singleton.  These garnered a fairly wide spread of opinion after they first came out from fantastic to "meh".  I think that was mainly because of very loose quality control and a reaction to the absurd price.  But my tube comes pretty close to the VT-231 - not as good but very credible so far.  For the next week or so the VT-231 stays in the Crack so as not to muddy the waters.  Considering I got the 1944 NOS VT-231 for $30 and the CV-181 for free, I won't be too hurt to go back to the CV4003 if I decide it suits me better later on.  Right now the 6SN7s are sounding very sweet.

[dludingt]

I second the sentiment on this improved adapter. I picked one up a month or so ago and the 6SN7s sound dead silent compared to the 12AU7. Highly recommended.

Doc, I wonder what it would cost to produce a PC board that would do this? Just like the power cord kit, it would be a great add on that everyone could make and use their choice of socket, etc.

[Paul Birkeland]

Doc, I wonder what it would cost to produce a PC board that would do this? Just like the power cord kit, it would be a great add on that everyone could make and use their choice of socket, etc.

There are many times where an adapter won't actually work.  If the 12AU7 is being heated by 12V, then the adapter won't work properly.  If the 12AU7 is being heated by a regulated rail of 6.3V, then adding the heavier load of the 6SN7 may cause the regulator to fail (expensive damage), especially if you're using a pair.

[Jeb Jeb]

Hi guys - I have a few 6SN7s so I picked up one of these adapters so that further down the line I could perhaps try them out in the Crack.  Although I'm a bit worried reading PB's post that using such adapters in certain applications could damage things.

Anyway, I received it today - and it's a nicely made little device!  As the earlier posts mention, when in the amp's socket the area between the adapter's ceramic socket and the board it is mounted on is exposed so needs covering, so I'll look into that.  The solder points on the bottom of the board are also still visible, and while unlikely to touch them it seems like they should be covered too just to be safe.

I was a little worried at first that the solder points on the underside of the board come quite close to the metal retainer ring on the Crack's tube socket.  There's a couple of mm of clearance and I don't believe they could come into contact - but I was wondering if that should be covered with something non-conductive too.

[btrancho]

Hi guys - I have a few 6SN7s so I picked up one of these adapters so that further down the line I could perhaps try them out in the Crack.  Although I'm a bit worried reading PB's post that using such adapters in certain applications could damage things.

Anyway, I received it today - as the earlier posts mention, when in the amp's socket the area between the adapter's ceramic socket and the board it is mounted on is exposed so needs covering, so I'll look into that.  The solder points on the bottom of the board are also still visible, and while unlikely to touch them it seems like they should be covered too just to be safe.

I was a little worried at first that the solder points on the underside of the board come quite close to the metal retainer ring on the Crack's tube socket.  There's a couple of mm of clearance and I don't believe they could come into contact - but I was wondering if that should be covered with something non-conductive too.

I've been using one of these for several months with no problems concerning the bottom solder points.  I did fill the area between the PCB and the ceramic socket with Sugru and it has eliminated the exposure issue.