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Old 25th May 2010, 10:34 AM   #1
el156 is offline el156  Portugal
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Default 6aw8-a tube question

Hi all !
I have some 6Aw8-A tubes that i would like to use in audio, but in this tube description says it contains high-mu triode and a SHARP-CUTOFF pentode, and my question is if this sharp-cutoff pentode is usable for audio! what sharp-cutoff means?
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Old 25th May 2010, 11:53 AM   #2
Arnulf is offline Arnulf  Europe
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It is the opposite of remote cut-off.

Remote cut-off means that gain "tapers off" towards the extreme of grid voltage instead of rapidly declining at some point, which in turn means the gain is not linear throughout the Vg range. This is useful for certain purposes (amplification of RF signals, especially in FM/limitting and AGC) but straight audio amplification isn't one of them (they could be useful in audio compressor circuits though).

Sharp cut-off means that gain is more linear with grid voltage and that tube will cut off (= current through it will decrease dramatically) at and below certain grid voltage. This is useful for audio since you get maximum linearity, as long as you don't drive the tube into cut-off, of course
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Old 25th May 2010, 12:58 PM   #3
el156 is offline el156  Portugal
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Quote:
Originally Posted by Arnulf View Post
It is the opposite of remote cut-off.

Remote cut-off means that gain "tapers off" towards the extreme of grid voltage instead of rapidly declining at some point, which in turn means the gain is not linear throughout the Vg range. This is useful for certain purposes (amplification of RF signals, especially in FM/limitting and AGC) but straight audio amplification isn't one of them (they could be useful in audio compressor circuits though).

Sharp cut-off means that gain is more linear with grid voltage and that tube will cut off (= current through it will decrease dramatically) at and below certain grid voltage. This is useful for audio since you get maximum linearity, as long as you don't drive the tube into cut-off, of course
THANKS
I will make some experiments and see how the sound is,maybe i will test it as phase splitter?
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Old 25th May 2010, 01:45 PM   #4
TheGimp is offline TheGimp  United States
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You might try the Pentode section at Ik=17.5mA, Vk=200V (supply around 300V), Vg=-2.5V with a 56K plate load as a gain stage. Pentodes tend to be a bit noisy due to partition noise, but it looks pretty linear there, although that is pretty hot for plate dissipation (3.5W) but below design max (3.75W).
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Old 25th May 2010, 02:40 PM   #5
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Quote:
Originally Posted by TheGimp View Post
You might try the Pentode section at Ik=17.5mA, Vk=200V (supply around 300V), Vg=-2.5V with a 56K plate load as a gain stage. Pentodes tend to be a bit noisy due to partition noise, but it looks pretty linear there, although that is pretty hot for plate dissipation (3.5W) but below design max (3.75W).

Gimpy,

It seems the triode is quite close to that found in the 12AT7. What's your opinion of using the 6AW8 in a Dyna/Scott style power amp front end? FWIW, I think that LR8 regulating g2 B+ (for linearity's sake), at 150 V., rates to be correct.
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Old 25th May 2010, 03:21 PM   #6
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Why not try the pentode-section only with a Schade-connected EL156. The pentode section could be used at Ua/Us 150V and Ia 20mA where it looks acceptable. The EL156 is quite unlinear when pentode-connected but will be helped by the local feedback over this tube only.
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Old 31st January 2011, 02:55 PM   #7
hooman is offline hooman  Iran
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shindo use 6aw8 in f2a amp . so i tested thise tube in 10 w se (6aw8+f2)amp ...pentode in first stage and input signal than triode ! never seen like 6aw8 in midrange
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Old 1st February 2011, 02:15 AM   #8
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Not specifically an audio type,but 6AW8's were widely used by AMPEX in the preamp circuits of their vintage professional tape recorders (602 , 354 , PR-10 , ...) , which are still appreciated today for their great sonic performances. A cheap and versatile tube with good audio potential: maybe a "sleeper" ?
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