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I am planning to build a Williamson tube power amp. The first stage is an anode load amplification using 12ax7.
I wonder what difference will make if I use an anode choke instead of an anode resistor?
Actually I ask this question 13 years ago on this asylum but with no feedback.
Alan
Follow Ups:
Use a 6J5 or 6SN7 and stick to the original design . Forget about plate chokes on the input stage . Even with a suitable valve instead of 12AX7 , you have a reactive component inside a feedback loop over several cap-coupled stages as well as the output transformer .
Al
Not a good idea for that tube. Like Triode Kingdom pointed out, because of the tubes high Rp you would need a super high L choke. Also, because the resistance of any choke would be considerably less than your load resistor, the plate of the 12AX7 would see a much higher voltage. This would definitely alter your tubes operating points (most likely in a less linear part of the tube curves), and quite possibly fry your tube because of too much dissipation.Edit: As JKT pointed out a properly implemented CCS would be a good choice, I use them a lot.
twystd
Edits: 06/24/15
To my way of thinking an anode choke load makes the most sense when faced with limited available B+, since the choke will swing about twice the applied B+. I doubt that is the case here. If you want to "improve" on a resistor load I would suggest using an active current source load. There are many candidates out there.
"It is better to remain silent and thought a fool, then speak and remove all doubt." A. Lincoln
IMO, very little positive difference for a 12AX7.
The choke allows high AC impedance without much DC impedance to allow for low DC voltage drop across the element. However, the 12AX7 runs at so low current that the drop in DC is not a big deal. A good resistor can sound great and give wider bandwidth.
Have you calculated the value needed to obtain good low frequency response with a 12AX7?
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No. Do you have any suggestions ?
I am thinking about the Lundahl LL11667 gapped at maybe 2-3mA which should have an inductance of over 500H.
Alan
I'm pretty sure 500H on top of a 'AX7 will put you down 6dB or more at 20 Hz. That's to say nothing of the low frequency phase shift. Doesn't seem practical to me.
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TK, would he still need to run a resistor, to get the proper voltage?
Maybe, but just as a drop resistor (before the decoupling cap).The inductive reactance of the choke is the impedance load for the tube's plate.
Just be sure to keep 100 volts or so across the CCS.
They sound better that way.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Edits: 06/25/15
whatever the inductor is, there is your resistor in from of the inductor. I like a RCL. I have had excellent results with inductor to load the plate and prefer it over a resistor but it depends upon the tube. I like it on a 76 or 27.
iBasso DX100,DX50 DX90. Chord Hugo. HiFiman 901 balanced. RSA Intruder, The Lightning. Fostex TH900 balanced, Hifiman HE-6, 560, 500, JH13 Pro balanced. Lyr2, Audeze. All phones balanced mostly with Whiplash cables. Photo gallery: www.pbase.com/jamato8
So the correct inductance value chokes will drop the voltage to similar value as the resistors? Like chokes can replace the 82K/100K plate loading resistors going to the PI tube?Thanks!
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Edits: 06/24/15
No, the DC value will drop in accordance with the choke's DCR. Inductance won't affect it.
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Buy Chinese. Bury freedom.
after all, different gauges would yield different results for the same henry even though the inductance remains the same.
I like using inductors as I find the sound is more liquid, dynamics are improved because as the field collapse you don't get the momentary sag and you are getting the benefit of the filtering.
iBasso DX100,DX50 DX90. Chord Hugo. HiFiman 901 balanced. RSA Intruder, The Lightning. Fostex TH900 balanced, Hifiman HE-6, 560, 500, JH13 Pro balanced. Lyr2, Audeze. All phones balanced mostly with Whiplash cables. Photo gallery: www.pbase.com/jamato8
mt
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