Cagomat - I am looking seriously at the C3o pentode. Please describe the sound differences between the C3o pentode and the C3g triode.
In my opinion the C3o sounds more neutral, smoother and less distorted. I can draw you a schematic when you want
I will also test the " bestpentode " circuit from Frank Blöhbaum. With this circuit you get less noise and distortion.
Thanks for that! I'd be interested to see how the ferrite beads are attached. Could you post a close-up photo?
Did you try without a cathode bypass? Or with a DC Link bypass?
Here you see a picture of my phono, I used shrink tubing over the beads. I use no cathode bypass, I use heater biasing with 12 ohm resistor
Are you measured (or calculated) the output impedance?
C3x tubes in pentode mode has -about- 200k Ri.
The main Influence of the output impendance is the plate resistor, its parallel to Ri and Rg1 of the next stage
It's manageable in phono (where the 40dB stage gain is advantageous), but -without another low output impedance stage- in amplifier as VAS stage, IMO is drawback.
Look at Yamamoto amplifier, they use the WE 717 and C3m pentode with very low current and higher output impendance to drive 300b 45 and AD1 and it sounds really good, or look at WE 310a or Thorsten Loesch legacy amplifier
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... and look another 99% of 300B amps, where not high Ri tube the driver.
Built 300B amp even with 12AX7, but I don't think this method should be the next "holy grail".
High gm pentodes very good drivers if connected as triode, the output impedance is a fraction of the pentode mode impedance, and large signal THD behaviour is also better even at HF region.
Built 300B amp even with 12AX7, but I don't think this method should be the next "holy grail".
High gm pentodes very good drivers if connected as triode, the output impedance is a fraction of the pentode mode impedance, and large signal THD behaviour is also better even at HF region.
Soundwise the C3m/C3o pentode wipes the floor with triode strapped D3a, E180F, E810F, C3m, C3g.........
I like the D3a as preamp tube but not as driver, but its only my experience and tastes are different.
I like the D3a as preamp tube but not as driver, but its only my experience and tastes are different.
So, Cagomat, how would this schematic be revised to eliminate the cathode bypass cap? Trying to eliminate all caps in the audio signal.
You can avoid the cathode bypass of C3o with heater bias, but you can not eleminate all caps in the signal path. The last power supply cap is in the signal path and you can not combine direct coupling with filament bias of the power tube. From my experience sounds a high value gridstopper much worse than a good cap