![]() That suits my mostly folk, blues, vintage rock music taste. That gives a bit of power amp compression due to supply sag when pushed hard (the attack is softened). That allows low hum with a power supply with only 50uF of HV filtering. I finally settled on fixed bias with individual bias adjustment for each tube so I could balance idle currents. cathode bias, common to both tubescathode resistor with no bypass cap. cathode bias, separate resistors and bypass caps on each tube I mucked about with output tube bias methods, I tried: My own guitar amp runs 6SL7 common cathode amp plus cathodyne splitter into a pair of 6V6. Zout(cathode) increases from 1/gm by a maximum factor of RL/uĪnd that is why the HiFi guys recommend use of a low mu tube.įor a guitar amp you want to emphasize some of the limitations of the cathodyne and you will find that using a high mu tube such as 6SL7, 12AT7, 12AX7 will impart that "warmth" from even harmonic distortion resulting from the asymmetry when over driving. Zout(anode) increases from 1/gm toward RL One of the best kept secrets for guitar amp, power amp design is to use a cathodyne (split load) phase splitter.Īll of the HiFi guys will tell you that the cathodyne works best with with a low mu tube, this is quite correct for a HIFi Power Amp.įor equal values of anode and cathode loads Zout at both anode and cathode is approximately = 1/gm What you lose inb terms of linearity, you probably gain back in reduced blocking distortion. (Works best if you include a DC coupled grid driver.) In this case (driving the finals directly off the cathodyne) you'd be better off with cathode (auto) bias. It's especially obnoxious when using fixed bias. Even if you don't hear the actual clip, this can still cause noticeable sonic degradation until that extra charge leaks off. Turning on the GK parasitic diode will charge the coupling capacitor negative, adding extra unwanted bias that forces operation more towards cutoff. RC coupling to finals can also lead to problems on overdrive. Open another current path (as will happen if the driven Vgk goes positive) and it'll go out of balance. The reason the cathodyne stays balanced is that there is just the one current path through the VT. The A Number One disadvantage to using a cathodyne as you propose is that it doesn't tolerate very well grid current. ![]() 6V6s aren't a hard load if you operate 'em as pentodes.
0 Comments
Leave a Reply. |