I have to admit I understand on a very cursory level. What I do understand is the red flag you are waving and appreciate it greatly. His recommendation is for the capacitor to be an electrolytic which will have polarity. Not sure if that is the missing element here? I am awaiting his response.
Apparently so does he. For someone to propose bypassing the cathode without discussing what to do about the nfb suggests that perhaps you should take your advice from other sources
No, the type of capacitor construction has nothing to do with anything. And it appears further bizarre that one would recommend a cap in the hundreds of uF and specify electrolytic. As opposed to what? 500uF ceramic?
I appreciate you muddling through my ignorance here. We all start somewhere. I am assuming that I have misunderstood his application. Perhaps you could read his quote on it here starting with section 6 and culminating in 7.
Chimera Labs Williamson Tube Amplifier Modifications
Since it does not seem to apply to the SXA power stage its mostly section 7.
In an email on to me on the SXA specifically he wrote,
" I would leave the resistance value for the ECC81 amplifier section alone. I
would replace the 2200 Ohm with a low noise metal film and I would add a
audio caliber bias capacitor in parallel with the 2200 Ohm resistor. I would
replace the 270K plate resistor with a high wattage 2 or 5 Watt Carbon Comp
or Carbon Film Resistor. Take a magnet to make sure the Carbons have copper
leads and end caps."
Chimera Labs Williamson Tube Amplifier Modifications
Since it does not seem to apply to the SXA power stage its mostly section 7.
In an email on to me on the SXA specifically he wrote,
" I would leave the resistance value for the ECC81 amplifier section alone. I
would replace the 2200 Ohm with a low noise metal film and I would add a
audio caliber bias capacitor in parallel with the 2200 Ohm resistor. I would
replace the 270K plate resistor with a high wattage 2 or 5 Watt Carbon Comp
or Carbon Film Resistor. Take a magnet to make sure the Carbons have copper
leads and end caps."
Yes indeed. I won't comment on the parts swapping or "audio caliber" nonsense, there has been plenty written on that.
There has also been plenty written on the deficiencies of the Williamson design, starting in the 1950s. Do a search. Bottom line, yes, improvements are possible and advisable, you must be able to draw loadlines and pick better operating points.
As far as the first stage cathode bypassing, that will increase the gain AND further increase the gain greatly by defeating the nfb. Do you want nfb? Do you want a different gain structure?
And no, there is no reason whatsoever for the bypass cap to be electrolytic or polar. If there was such thing as a 500uF film cap of reasonable size (there isn't), than that would be preferable.
There has also been plenty written on the deficiencies of the Williamson design, starting in the 1950s. Do a search. Bottom line, yes, improvements are possible and advisable, you must be able to draw loadlines and pick better operating points.
As far as the first stage cathode bypassing, that will increase the gain AND further increase the gain greatly by defeating the nfb. Do you want nfb? Do you want a different gain structure?
And no, there is no reason whatsoever for the bypass cap to be electrolytic or polar. If there was such thing as a 500uF film cap of reasonable size (there isn't), than that would be preferable.
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