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Substitute for 6SC7 in preamp?

 
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Cygnus X1



Joined: 22 Apr 2008
Posts: 915
Location: Midlands South Carolina

PostPosted: Thu Mar 26, 2009 9:13 am    Post subject: Substitute for 6SC7 in preamp? Reply with quote

'm playing with a Fender Tweed circuit-a 5C3.
Not vintage, it's a project homebrew.

I was wondering what other octal tubes might be subbed for the 6SC7 preamp tubes to get a bit more headroom?
For those not familiar, Fender switched to a 12AY7/12AX7 later in this 2x6V6 powered amp.

Preferably with the same pinout.
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martin manning



Joined: 06 Jul 2008
Posts: 5399
Location: Queen City

PostPosted: Thu Mar 26, 2009 11:31 am    Post subject: Reply with quote

Info here:

http://thetubestore.com/earfenam.html

I just Googled 6SC7 substitute. The chance of finding something with the same pin-out looks slim, but since it's a homebrew, you could rewire it to use another type. 6SL7 is a replacement (with rewiring) but you are looking for more than that... check the specs on 6SL7, and its substitutes 5691, 6113, or 6188 to see if one of them might get you more headroom.

MPM
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Phil_S



Joined: 23 Oct 2007
Posts: 3730
Location: Baltimore, MD

PostPosted: Thu Mar 26, 2009 1:24 pm    Post subject: Reply with quote

Commonly available octal dual triodes are 6SN7 (very much like a 12AU7) and 6SL7 (like a 5751 and probably closest octal sub for a 6SC7). One big difference between 6SN7 and 6SL7 vs 6SC7 is that the 6SC7 has a common cathode for both sections, making it less flexible.

The 6SN7 might not have enough gain and to low a plate resistance to drive the circuit, but it will clean up a bit due to much lower gain. The 6SL7, while about the same gain factor as the 6SC7, has a lower plate resistance, and just might be the ticket you are looking for. Since the cathodes are split on the 6SL7, you can just put a jumper on the cathode pins and that will work.

6SN7 and 6SL7 have the same pin out. 6SC7 has a different pin out, so you will need to rewire the grids and cathodes. Plates and heaters are the same.
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