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Can 6SL7 replace 6SC7?


 
6/10/2003 11:29 AM
Keith
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Can 6SL7 replace 6SC7?
Greetings,  
 
I recently acquired a 1952 Gibson GA-30A, with 3 metal preamp tubes; 2x6sj7's, and a 6SC7 as a PI. It is quite a basket case (One shredded speaker, had to replace the AC cord, etc.) but I'd like to revive this old classic. The 6SJ7's test OK (I have several glass 6SJ7's as spares) but the 6SC7 tests as dead and I have no replacement. I would really like to fire this beast up! Perusing my copy of the recieving tube handbook, I noticed that the 6SL7 has nearly identical specs, but a different pinout. The 6sc7 uses a common cathode for both triodes, whereas the 6SL7 has independent cathodes. Can I connect the catrhode pins on the socket and match the other pins to the correct pinout in order to substitute the 6SL7, or is there some compelling reason not to do this? Thanks in advance!  
BTW, Are there any online sources for a schematic for this model? Pittman's book contains a later model of the GA-30, but not this one.  
 
Keith
 
6/10/2003 3:29 PM
steve m
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Keith,  
 
You've already answered your own question, if the specs are the same for both tubes, but have different pinouts, just hook up the socket so you can use the 6SL7 as a substitute.  
 
If you have a fast connection, try this site:  
 
http://www1.korksoft.com/~schem/manualheaven.htm  
 
The Gibson Master Service Manual has lots of schematics for obscure versions of their amps, but the file is 173 megs, so it will take a while to download over a fast connection.  
 
Hope this helps,  
 
Steve
 
6/10/2003 9:45 PM
Keith
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Thanks, Steve, I've found in the past that it's usually a good idea to check with the gurus on Ampage before I start anything this major...  
 
Thanks for the heads-up on the Gibson Schematics!  
 
Keith
 
6/10/2003 9:51 PM
steve m
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Keith,  
 
I don't really consider myself a "guru" :)  
 
Glad to help out on the Gibson manual, it is a real godsend for owners of Gibson amps.  
 
Steve
 
6/11/2003 1:14 PM
Wild Bill
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Keith, the 6SL7 has tons more gain! It would be similar to subbing a 12AX7 for a 12AU7,  
 
This is not necessarily a bad thing! You might like the tone but it will definitely be quite different.  
 
You should also look at the plate/cathode resistor values. They will be all wrong for the new tube. Any 12AX7 circuit should be close enough.  
 
Of course, we're talking a lot more work and a serious change to the amp's character. If you want to preserve the tone then simply buying a 6SC7 is the easy fix. If you don't care about keeping things stock then - just go nuts on it and solder away!  
 
Wild Bill
 
6/11/2003 3:50 PM
Bruce /Mission Amps
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No, they both have a mu of around 70 Bill.  
Maybe you were thinking 6SN7 vs 6SL7.  
I've rewired the octal sockets in many old tweed amps for glass 6SL7s in place of metal 6SC7s  
They don't sound exactly the same but still sound really good and are fairly inexpensive.  
 
 
Bruce
 
6/11/2003 5:34 PM
steve m
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To add to what Bruce said, I see nice NOS 6SL7s for sale at Hamfests cheap, all the time. All of them have been glass, I don't think I've ever seen a metal 6SL7. I've never seen a glass 6SC7 for sale, and very few metal ones.  
 
I had an old 5D3 or 5B3 tweed Deluxe that had glass 6SC7s in it. I tried some metal ones I, but couldn't hear any tonal difference, FWIW.  
 
Steve
 
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