Different octal adapter question

[stereorob177]

Greeting folks, from a new member!  I've ordered the Crack/Speedball kits and am considering installing an octal socket where the 9-pin usually goes. I've read here how adapters have been used so that allow an octal tube in the stock 9-pin socket (ie 6sn7). My question is can I do the opposite?

I have a small collection of old stock 6sn7 tubes I want to try and I have an adapter that fits an octal socket for a 6sn7 and is wired to accept a 12au7. Would this work from a wiring/heater voltage point of view? I feel that I'll likely end up using a 6sn7, but still want the option of using a 12au7 with the adapter. (I also think a 12au7 would look nice sitting atop the adapter!)

Appreciate all I've been reading so far,
Rob

 

[Paul Birkeland]

Hello Rob,

Going with the octal socket, then the adapter made to adapt 6SN7's to 12AU7's will work out just fine.

What you may have some trouble with is fitting the octal socket onto the chassis plate, it gets a little tight up there!

 

[Grainger49]

Rob,

Take a quick look around the Crack folder and you will find a number of first time builders who had a string of problems because they didn't build stock first. 

You might not be a first time builder, just a first time Bottlehead.  If so, ignore the above warning.  Otherwise my suggestion is to get the adapter and see if you like the 6SN7 better.  NOS 6SN7s are pretty pricey these days, nos 12AU7s a bit less so.  And then Paully (a poster here) put in 7N7s in his FP III, a version of the 6SN7 that costs much less because it is an odd tube. 

 

[stereorob177]

Blackplate/Grainger,  Thank you both for the quick replies. Good to know my plan can work, albiet with precautions as per your warnings. Yes, I see that old stock 6sn7s are not cheap these days. Luckily I was gathering a stash about 12 or so years ago for another, similar project and still have 10 - 15 different 6sn7 tubes and variants to try, including a nice single Brimar that I never did find a twin for but sounds great and is not microphonic.

Cheers!
Rob

 

[Grainger49]

Rob,

With an old stash bought at yesterday's prices, you are in high cotton!

 

[Laudanum]

Welcome aboard Rob !!!

Those 6SN7's that make the top 5  lists are indeed expensive.  But there are still some very good sounding tubes that can be had for very good prices with some searching and patience.  For example, Sylvania 6SN7 GTA and GTB can be found for pretty cheap and I dont find them having to apologize all that much to the Sylvania VT-231's which are on most of those top 6SN7 lists and are usually far more expensive.   I've also found a few relabeled Sylvania VT-231's for cheap.  Of course all this is ear and gear related so YMMV.   But you sound like you are in good shape with your stash.  Just pointing out that, depending on which tubes you fancy, there may still be some bargains out there.

BTW, I was running a 6SN7 in Crack with an adapter.  It was my preferred tube when Crack was a stand alone.  I built Foreplay III for 6SN7's and running in front of Crack, went back to 12AU7 or 12BH7 in Crack (currently 12BH7) with the 5998 output tube.  Good advice offered about initially building Crack stock with the 9 pin socket.  You can use a 12AU7 to 6SN7 adapter to roll your 6SN7's and compare with 12AU7 and compatible drop-ins.  You never know what you may end up doing in the future.  I also considered replacing the 9 pin with an octal socket in Crack.  Im glad I didnt because, as mentioned, a I expanded the headphone system I found that I preferred the 9 pin driver tubes in Crack when I built FPIII for 6SN7's.   You can always enlarge the hole later but it is a bit tight as is already, as Paul B. mentions.

 

[stereorob177]

Laudanum, interesting points. In fact I recall reading here about your 6sn7/12au7 switcheroo. I had built (with help from a builder friend) the headphone amp in headwize site's library - the one designed by Eric Barbour - which uses 6sn7 with 6bl7 as a follower. This also served as my preamp for these last 12 years or so and I always enjoyed the sound. Just could never get rid of a small hum, not too noticeable but occasionally annoying. Then recently I got a new preamp from that same builder friend which uses 12au7 tubes - excellent, quiet pre. So you see, I now have the opposite situation you do! ;-)  I'll be feeding the Crack from the new pre, so I may end up with a 12au7/6sn7 combo as well.

I'm very much looking forward to the first listen!

Rob

 

[Laudanum]

Laudanum, interesting points. In fact I recall reading here about your 6sn7/12au7 switcheroo. I had built (with help from a builder friend) the headphone amp in headwize site's library - the one designed by Eric Barbour - which uses 6sn7 with 6bl7 as a follower. This also served as my preamp for these last 12 years or so and I always enjoyed the sound. Just could never get rid of a small hum, not too noticeable but occasionally annoying. Then recently I got a new preamp from that same builder friend which uses 12au7 tubes - excellent, quiet pre. So you see, I now have the opposite situation you do! ;-)   I'll be feeding the Crack from the new pre, so I may end up with a 12au7/6sn7 combo as well.

I'm very much looking forward to the first listen!

Rob

I guess I could have gone the same way by building the FPIII as stock with the 12AU7's and then using the 6SN7 in Crack.  Really enjoyed the 6SN7's though, and fortunately, no hum.  I went on a hunch really, expecting to go back to 12AU7's in Crack after the FPIII build.  I thought it would be a good compliment and I think it is.  Although I am currently running 12BH7 in Crack, Im not tied to it and 12AU7's will get rolled back in.  Just part of the fun