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previous: steve The octal tube (twin diode,single t... -- 10/8/1997 1:50 PM View Thread

Re: 6SQ7GT or 12SQ7GT

10/9/1997 12:16 PM
Re: 6SQ7GT or 12SQ7GT
The other octal triode with mu=100 is a 6SF5. It's the same as a 6SQ7 w/o the detector diodes.  
The 6SL7 dual triode is the one closest to a 12AX7 in gain characteristics, with a mu=70. In fact it was used extensively in audio circuits prior to the 12AX7. Look at some of the old Ampeg schematics.Some players still swear by the tone of the old octal tube version Reverborocket.  
The 6SC7 is like a 6SL7, but has a common cathode and can't really be used as two independent triodes. These tubes are usually seen in preamp mixer circuits and cathode coupled phase inverters.  
A large number of the 8-pin tubes are highly microphonic, especially the metal ones. You have to select carefully for the ones w/o loose elements, and sometimes it's advantageous to rubber mount the tube socket to the chassis. One selling feature of the "new" miniature tubes was that they were less susceptible to vibration.  
The glass (GT) versions of these octal tubes are the ones I've had the best luck with, but not all metal tube types have glass counterparts. Although the metal tubes have a sort of built-in shield which the glass tubes don't, their downfall is that their vacuum degrades over time.  
A current guitar amp that has an octal input tube is one model of George Alessandro's "Hound Dog" amps. I think it was the Redbone model, but don't hold me to it. These amps have a warm, fat tone.