I think one of the best things about tube amps is the fact that they're fussy. I love the sound of my Pass XA-25 but it just sits there. Looking at glowing tubes, swapping 'em out for others, adjusting bias (I used to do that with my Jolida) before my current tube amps no longer required it. Tubes, although often hot, are cool. I still really enjoy my little Dennis Had amp from time to time, and at least always have a quartet of old GEs glowing in my preamp. My guitar amps have tubes but you can't see them (the tubes, not the amps).
Tube amps - what 3 things…
I am close to purchasing a tube amp moving away from SS. So far I have listened to a pure sound, PL, and allnic.
Question for all you experienced owners - if you could do it all over again, what 3 things/features would you look for in an amplifier and what 3 things/features would you not invest in again?
- 92 posts total
Hi @atmasphere ,
I know that cathode bias is still cathode bias with any cathode capacitor value. But the cathode to ground impedance is realy very different. On 20 Hz with standard 100uF the impedance is Z=80 Ohm, 10000uf Z=0.8 Ohm, 100000uF Z=0.08Ohms.
@alexberger The impedance does not set the bias value- the DC resistance does. I'm sure the capacitor (and its quality) affected the sound quality! A tube amplifies due to the difference between the grid and cathode voltages- essentially as a differential amplifier. The cathode bypass allows the ground 'signal return' to be part of the gain structure of the circuit- essentially increasing its gain.
If you enjoy this sort of tinkering, here's a tip: figure out what the timing constant in the power supply is that feeds that tube. Then make sure that the timing constant of the cathode circuit is a little bit higher (by at least an octave) than the timing constant in the power supply. To this end, to prevent phase shift at 20Hz you'd want the cathode circuit to be good to 2Hz, so the power supply leg should go even lower. In this way the tube will be less able to modulate the power supply leg, which will reduce IM distortion.... Have fun!!
Hi @ideal8592 ,
In my case 100uf/16v were Black Gate CE W (M).
10000 were the same Black Gate + Nichicon Muze 10000uf/16v.
100000 were the same Black Gate, Nichicon Muze + Nichicon KA 9x10000uf/16v + Elna 3300uF/10v
It wasn't my "invention". At least dozen DIY people tried it many years before me. You can try yourself and it works!
- 92 posts total