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Old 11th May 2007, 05:43 AM   #1
jarthel is offline jarthel  Australia
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Default 6gu7 a sub for 6cg7/6fq7?

according to nj7p website, I can substitute a 6gu7 in place of 6cg7/6fq7.

Any thoughts on this?

thank you.
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Old 11th May 2007, 07:25 AM   #2
Colt45 is offline Colt45  Serbia
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The tube NJ7P lists as substitutes aren't always the same. "preferred substitutes" are usually pretty close.

6GU7 seems to draw more current at the same Va / Vg.

at 250v / -10v 6GU7 pulls double what a 6FQ7 does.
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Old 11th May 2007, 01:47 PM   #3
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I found a large stash of 6GU7's so I plugged one into the driver stage on my 300Beast amp, which uses 6FQ7's in SRPP. It sounded dull and lifeless. I tried a few different tubes with the same result. I did not try to optimize the circuit in any way, or even measure the currents to see what was going on. This does not imply that the 6GU7 sucks, only that it is not a drop in replacement for the 6FQ7.

The 6GU7 was used as a linear amplifier in the color circuits in TV sets. This implies that a good linear audio amp could be made from it. It may not be linear at the signal levels or bias currents that I was running.
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Old 11th May 2007, 02:12 PM   #4
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The 6GU7 is essentially a 6 volt 12BH7. Set it up like you would a 12BH7 (with the proper heater voltages of course!) and you can get good results. But it is not a good sounding 6CG7/6FQ7 sub.
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Old 17th May 2007, 04:20 AM   #5
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Hmm. Are there any very close matches? Would something like a 7AU7 work instead? Seeing that most heaters run a little hotter than usual, is there any harm in plugging a 7AU7 where a 6CG7 one was? For example, in a Williamson EL34 amp I completed recently.
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Old 17th May 2007, 08:35 AM   #6
Colt45 is offline Colt45  Serbia
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Why 7AU7? Thats not exactly a 6CG7 sub either.

You could rectify the 6.3v winding, get ~8v, and use an 8CG7...

They're dirt cheap, couple 3 bucks a piece, because they were used in series heater tv sets.. lots of them no less.
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