Besides the low frequency response established by the RC connection between driver and next stage ( output in this case ) ..........;the loading of the driver tube is not only factor of the anode loading rsistor of the driver but resulting of the combined combination of anode load and the RC loading ..( grid resistor ).........changing one of them will impair also the response of the whole amplifier . Have a nice day ...............2A3 amplifiers are always interesting ....
I havent't watched the results yet but 330K grid R and the choosen valu of the cap seems to be a GOOD choice........have few doubts this may bring the amp to sing as should a 2A3 do .....the smaller value of the coupling cap is also less inductive and less current draw on the driver .......both tubes benefit and don't worry , be happy .......
Great video. I have only been able to hear a small number of modern tube amps. I own a newer and two old tube amps. I still like my old amps best. The new one has better low end but sounds more like solid state. I like that classic sound of tubes.
Ha! Interesting insights, much appreciated :). Nice to see the results of the experiments - that Analog Discovery certainly comes in handy! Got some ideas for further experiments: 1. change the coupling cap alongside grid leak resistor - so that the RC time constant stays the same, preserving the frequency response and phase characteristics of the high pass filter 2. make sure you don't load the driving stage too much, stay within Rg at least 10 times plate resistance. 3. test on different types of tubes - small signal triodes, power pentodes etc. I tend to use 470k in my designs, sometimes going up to 1M...1M2 on voltage amplification stages, sometimes going down to 330k on big power tubes (EL34 etc.). Haven't really measured the distortion characteristics - it's a very nice idea to experiment though!
Great video!! This is Science that tells how to grossly voice an AMP and when you're an "Old fatrt" that can't really hear beyond 12K for most of us will insure where your trade offs can be...
Interesting effect and feels counter-intuitive to me. I'd have thought that if the gridleak resistor of the power tube is low, the driver tube would have to work much harder and thus be more prone to distorting. But it's the other way around. Hmm....
It likely is distorting more, but given it's 180 deg out of phase, it cancels the 2H distortion of the output tube. At least that's what I think is happening.
@@Keith-ux9kuI am wondering that also. Is the 0.22 cap a guess? Could you have left it unchanged and got the same result just from changing the grid leak value?
This is just 2nd order cancellation I think. If you analyze the two stages separately I would guess you'll see the driver distortion rise with the smaller grid leak as expected. But since the stages operate 180 degrees out of phase, it's cancelling the 2nd order harmonics similar to how a PP amp does. Reducing the driver distortion reduces the cancellation effect so the output even-order harmonics increase.
Genius changing a grid leak resistor/cap brings benefits for tonal richness etc....what a great result Steph
Very nice, detailed analysis. Audio Analyser is quite a handy tool it seems!
Great investigation. I really learned something here. That's why I like your channel so much!
Besides the low frequency response established by the RC connection between driver and next stage ( output in this case ) ..........;the loading of the driver tube is not only factor of the anode loading rsistor of the driver but resulting of the combined combination of anode load and the RC loading ..( grid resistor ).........changing one of them will impair also the response of the whole amplifier .
Have a nice day ...............2A3 amplifiers are always interesting ....
Absolutely fascinating. Learnt a lot. Sincere thanks. 👍
Glad it was helpful!
I havent't watched the results yet but 330K grid R and the choosen valu of the cap seems to be a GOOD choice........have few doubts this may bring the amp to sing as should a 2A3 do .....the smaller value of the coupling cap is also less inductive and less current draw on the driver .......both tubes benefit and don't worry , be happy .......
Great video. I have only been able to hear a small number of modern tube amps. I own a newer and two old tube amps. I still like my old amps best. The new one has better low end but sounds more like solid state. I like that classic sound of tubes.
I appreciate the research on this design consideration
Hands down the best tube amp channel out there. You rock! ❤
Wow, thanks!
Ha! Interesting insights, much appreciated :). Nice to see the results of the experiments - that Analog Discovery certainly comes in handy!
Got some ideas for further experiments:
1. change the coupling cap alongside grid leak resistor - so that the RC time constant stays the same, preserving the frequency response and phase characteristics of the high pass filter
2. make sure you don't load the driving stage too much, stay within Rg at least 10 times plate resistance.
3. test on different types of tubes - small signal triodes, power pentodes etc.
I tend to use 470k in my designs, sometimes going up to 1M...1M2 on voltage amplification stages, sometimes going down to 330k on big power tubes (EL34 etc.). Haven't really measured the distortion characteristics - it's a very nice idea to experiment though!
Great video Stephe. Your process and knowledge is very impressive
congrats Stephe 🙂!
Great video!! This is Science that tells how to grossly voice an AMP and when you're an "Old fatrt" that can't really hear beyond 12K for most of us will insure where your trade offs can be...
It would be interesting to know how a grid choke would sound?
Ha ha I’m first again…Skunkies biggest fan!
Interesting effect and feels counter-intuitive to me. I'd have thought that if the gridleak resistor of the power tube is low, the driver tube would have to work much harder and thus be more prone to distorting. But it's the other way around. Hmm....
How did you pick the.22 value for the capacitor?
It likely is distorting more, but given it's 180 deg out of phase, it cancels the 2H distortion of the output tube. At least that's what I think is happening.
@@SkunkieDesignsElectronics Aaaaah, that sounds like it makes sense
@@Keith-ux9kuI am wondering that also. Is the 0.22 cap a guess? Could you have left it unchanged and got the same result just from changing the grid leak value?
I choose it based on the low frequency rolloff point. Vcap has a great calculator.
This is just 2nd order cancellation I think. If you analyze the two stages separately I would guess you'll see the driver distortion rise with the smaller grid leak as expected. But since the stages operate 180 degrees out of phase, it's cancelling the 2nd order harmonics similar to how a PP amp does. Reducing the driver distortion reduces the cancellation effect so the output even-order harmonics increase.
Exactly what is happening.