6aw8-a tube question

el156 · 25th May 2010, 10:34 AM

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?
Thanks

Arnulf · 25th May 2010, 11:53 AM

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

el156 · 25th May 2010, 12:58 PM

Quote:

Originally Posted by Arnulf

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?

TheGimp · 25th May 2010, 01:45 PM

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).

Eli Duttman · 25th May 2010, 02:40 PM

Quote:

Originally Posted by TheGimp

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.

revintage · 25th May 2010, 03:21 PM

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.

hooman · 31st January 2011, 02:55 PM

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

Tubologic · 1st February 2011, 02:15 AM

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" ?

25th May 2010, 10:34 AM	#1
el156 diyAudio Member Join Date: Apr 2010 Location: ALBUFEIRA ;PORTUGAL	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? Thanks

25th May 2010, 11:53 AM	#2
Arnulf diyAudio Member Join Date: Feb 2009	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 __________________ mod verb, transitive /mod/ to state that one is utterly clueless about the operation of device to be "modded" and into "fixing" things that are not broken; "My new amplifier sounds great so I want to mod it."

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25th May 2010, 01:45 PM	#4
TheGimp diyAudio Member Join Date: Aug 2009 Location: Johnson City, TN	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).

25th May 2010, 03:21 PM	#6
revintage diyAudio Member Join Date: May 2007	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.

31st January 2011, 02:55 PM	#7
hooman diyAudio Member Join Date: Nov 2008 Location: tehran	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

1st February 2011, 02:15 AM	#8
Tubologic diyAudio Member Join Date: Dec 2004 Location: Brussels	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" ?