the fires are still burning
The 12AU7 was designed for radio-tv service and as general purpose amplifier as were many tubes. Types such as the 'AX7, 'AY7, 6SC7 etc. were deisgned for AF from the onset. A lot of tubes were adopted for AF service. It does not mean you should not use a tube for a type of service/application simply just because it was not specifically (originally) designed for it. Within specs of course!
Look at types 6DJ8/6922/ECC88, 5965, and so on. I''l bet 10-20 years from now you'll get somebody on the web saying the 5965 is an audio tube when we all know it was designed as a computer tube.
On a sandy note a lot of manufactuers used Hi-Gain Low-Noise RF transistors for AF amplifier use!
BTW Geeitar amps are all about flavor!
Cheers
Wayne
edit: If you use a 'AU7 as a CF or concerta of course it's going to be linear!
The 12AU7 was designed for radio-tv service and as general purpose amplifier as were many tubes. Types such as the 'AX7, 'AY7, 6SC7 etc. were deisgned for AF from the onset. A lot of tubes were adopted for AF service. It does not mean you should not use a tube for a type of service/application simply just because it was not specifically (originally) designed for it. Within specs of course!
Look at types 6DJ8/6922/ECC88, 5965, and so on. I''l bet 10-20 years from now you'll get somebody on the web saying the 5965 is an audio tube when we all know it was designed as a computer tube.
On a sandy note a lot of manufactuers used Hi-Gain Low-Noise RF transistors for AF amplifier use!
BTW Geeitar amps are all about flavor!
Cheers
Wayne
edit: If you use a 'AU7 as a CF or concerta of course it's going to be linear!
When the 'AU7 became popular as an audio tube they came out with the "A" version, less microphony, lower interelectrode capacitances. About the same time the "A" version of the 'AX7 and the 'AY7 appeared. BTW I've seen the 'AX7 used in multi-vibrater (osc.) service in older TV's. Probably remote control; don't remember for sure. Another nice radio-TV tube is the 6BN8. A good hi-gain (mu=70) triode hiding in there amongst the twin diodes! A big brother of the 6AT6.
Wayne
Wayne
12AX7 vs 12AU7
The 12AU7 is certainly a good audio tube; they have been used in many amplifiers over the years with good results.
They are not usually used in preamp stages because gain is lower than most designers desire, so 12AX7 is preferable.
!2AU7 is commonly used to drive power (output) tubes because it can provide more drive current than the 12AX7 can; better impedance match in most cases there.
Both tubes have good linearity if properly biased for the specific circuit requirements.
The 12AU7 is certainly a good audio tube; they have been used in many amplifiers over the years with good results.
They are not usually used in preamp stages because gain is lower than most designers desire, so 12AX7 is preferable.
!2AU7 is commonly used to drive power (output) tubes because it can provide more drive current than the 12AX7 can; better impedance match in most cases there.
Both tubes have good linearity if properly biased for the specific circuit requirements.
I tried some months ago using tubes at very low voltages such as 30 volt. Using an asymmetrical SRPP I got the best results on THD using 12AU7, and to be more specific an ECC82 by Philips Miniwatt. I tried also 6SN7 but wasn't so linear at that point. So I suggest using it for low voltage designs. Viceversa I tried 12AU7 at normal voltage and I can't get the same low distortion. For me the best tube in term of THD is 6SN7.
I am not going to join a discussion that is very often a "horses-for-courses" thing, where THD does not tell the whole story. E.g. if the distortion in a twin triode is mainly 2nd harmonic but it is used as a push-pull driver, the results might well be acceptable, etc.
But just to mention that a so-called high gm triode such as the ECC88 is not very different in characteristics at 1 - 2 mA from the ECC82 types (a little higher mu). It will be noticed that such operation is very dependant on anode current, i.e. the rp and gm curves have a high slope in the low Ip region, compared to the intended region of 10 - 20 mA. This might well lead to measured differences with slightly different component values, something the designer should be aware of.
As a p.p. driver for a low impedance high output swing stage I have used an E182CC, which is decidedly not an audio tube (it is a computer switcher), but it filled the role admirably, apart from differences between the 2 triodes sometimes.
Regards.
But just to mention that a so-called high gm triode such as the ECC88 is not very different in characteristics at 1 - 2 mA from the ECC82 types (a little higher mu). It will be noticed that such operation is very dependant on anode current, i.e. the rp and gm curves have a high slope in the low Ip region, compared to the intended region of 10 - 20 mA. This might well lead to measured differences with slightly different component values, something the designer should be aware of.
As a p.p. driver for a low impedance high output swing stage I have used an E182CC, which is decidedly not an audio tube (it is a computer switcher), but it filled the role admirably, apart from differences between the 2 triodes sometimes.
Regards.
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