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hagtech wrote:

The issue I see is that of intermodulation distortion on the biasing of the output tube.  It will effectively change HF operating point per supply ripple.  Easy to understand if one imagines a gross ripple of 50V.  Same thing happens with 0.5V ripple, just to a lesser extent.

Jim, I do not know – it is not so clear to me. First of all the subject of the intermediation is kind of complex.  The contemporary ceramic dives in soft runner suspension have intermediations (via Doppler) order of magnitude higher then compression driver and it doses not prevent them to accepted by morons as “good drivers”. I was thinking abut it before and I do admit that in the case of high ripples the modulations might take place from DC ripples  on plate to AC plate but to which degree I do not know. From one point it is very easy to measure the change of intermediations with change of ripples but from another point I do not know what that measurement would mean. Also I do not know where the subjective problem of intermediations would compete with subjective benefit of lowering capacitance. My objective is to find purely subjectively an equidistant between the minimal capacitance (with presumption that smaller cap would allow to use better cap) and the negative subjective sensation that high ripples might be resulted).  With full a range Milq the minimal capacitance of the last 6C33C cap was 750uF but it was restricted purely by noise. In biasing of 6E5P the minimal capacitance after gas tube is 10uF and it is purely sonic value. I was experimenting in there with everything, starting from no-capacitance and ending with 100uF and in there it is MUCH more critical as I is right on grid). For whatever reason the 10uF was a dead spot where everything come together… So, I presume and hope that the 6E5P plate, in my application, might have own max tolerable ripples and min capacitance. I am not certain in it but I do have a hunch that it might be much smalls capacitance then I ordinarily put in…

hagtech wrote:

In my latest ongoing amp project I re-discovered an easy way to deal with some ripple.  The stage runs large bypass cap from B+ to cathode to keep output loop small.  Only thing left is grid.  I drive the grid through an interstage tranny, and set the common mode of the secondary to ground via 50k resistor.  This is for dc bias.  The trick now is to run a 1uF or so cap from B+ to the common mode of the secondary (in my case a center tap).  Thus, any ripple on B+ is also exactly seen on cathode and grid.  The tube has no idea anything is going on, as it only sees a constant dc bias at all terminals.  I got this idea from a WE92A schematic.  It works incredibly well.  My noise floor (on proto) dropped maybe 20dB or more.

Yep, the idea to have the enter tube to “float on ripples” is elegant but from my point of view it is not the way to fight with problems the ripples might course. You might make the tube impervious to ripples but look how much you pay to do so: pollution of cathode, pollution of grid… in the case of DH you would need to pollute the filaments… Is it worth it, Jim? BTW, some of aspects of your “float on ripples” idea, viewed from a dissimilar angle, is something that Dima and I recently “re-invented” for a VERY different and for almost “revolutionary” application. I am sure the readers of my site will be reading about it in a coupled mouth if the implementation demonstrates itself sonically positive.

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