link to technical page

[John Roman]

I've been looking for some technical advise.  I'm converting my extended foreplay 3 for use with 6sn7 output tubes, leaving the 12au7 in place as the shunt regulator. I usually strafe the archives before asking but sometimes have trouble locating what I'm after. I just want to be sure what I'm doing is correct. Can someone point me to a specific link that gives specifics to the above change, in it's entirety? Pin outs from the 9 pin 12au7 to the 8 pin octals and correct location of all resistors and such? I've tried to accomplish this on my own and have just gotten more confused than anything. Oddly enough, I believe I'm actually learning something though..... about time I'd say!
Hey Doc,
I saw a post from back in 08 that you were planning on setting this "link" up. Does it already exist? My apologies if it already does. Just having too much trouble getting this small change resolved. Your help is greatly appreciated.

[Doc B.]

I don't think a step by step was ever written for this. Basically you look up the 12AU7 pinout and the 6SN7 pinout and just move the stuff connected to a given pin on the 12AU7 to the corresponding pin on the 6SN7. The only thing slightly tricky is that the 4-5 heater connection on the 12AU7 goes to a single pin, say, 7 on the 6SN7 - and the pin 9 connection on the 12AU7 then goes to pin 8 on the 6SN7 (and you have to adjust the resistor in the heater power supply). Whenever there is something connected to the center pin of the nine pin 12AU7 socket (like the LED), look at where the wire coming off the center pin goes (ground). Just remove that wire and connect the LED directly to ground when you install the 6SN7 socket.

(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fdiyaudioprojects.com%2FSolid%2F12AU7-IRF510-LM317-Headamp%2F12AU7-ECC82-pinout-diagram.png&hash=1f2278160ced25153cdc5b98b07cad030ec1513a)(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fupload.wikimedia.org%2Fwikipedia%2Fen%2F4%2F4e%2FEIA-8BD.png&hash=942bc05c0c9e309434e358cb234e41543f095317)

1 on the 12AU7 goes to 2 on the 6SN7

2 on the 12AU7 goes to 1 on the 6SN7

3 on the 12AU7 goes to 3 on the 6SN7

4 and 5 on the 12AU7 goes to 7 on the 6SN7

6 on the 12AU7 goes to 5 on the 6SN7

7 on the 12AU7 goes to 4 on the 6SN7

8 on the 12AU7 goes to 6 on the 6SN7

9 on the 12AU7 goes to 8 on the 6SN7


IMO if one wants to hear the 6SN7 sound you can get pretty close by doing a much easier conversion to 6CG7. I know some will strongly disagree with this. The 6SN7 sound just happens to not really be my thing.

[Laudanum]

Hi John.  If I can do it, you can do it.  Mines not the extended but a photo may help nonetheless.
My 6SN7 socket is labeled with the pin conversion numbers.  They are probably hard to read anyway but dont let it throw you off.

(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fi130.photobucket.com%2Falbums%2Fp243%2FBlueThomas%2FBottlehead%2FFPIII6SN7.jpg&hash=5ad47f087a46d490ff423286cfb86c95af660c91)

(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fi130.photobucket.com%2Falbums%2Fp243%2FBlueThomas%2FBottlehead%2FFPIII6SN72.jpg&hash=dfc5f5099c414a893c14a0e6306a6010c036b23e)

[John Roman]

Thanks Desmond,
Yeah photos do help. I'm just worried I'll mess up my pre amp. I think I've got it....

[Grainger49]

Something like the information in this thread:

http://www.bottlehead.com/smf/index.php/topic,2153.msg16622.html#new