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cv wrote:

I've only heard the 801 in class A2, but I can easily imagine that the 10Y or 801 with nickel output would offer the purest possible sound in the 1k-10k range, such that it is the S2's true voice you are hearing. It's something I'm going to pursue when I have time/funds... Alas I do think that your existing amp platform (i.e. B+ voltages) is not optimal for 10Y; the DC coupling would be out etc and this may well swamp the differences between tubes.

Yep, this is one of the reasons why I do not do it. I have some very cool 10Y but the plug-and-play with 10Y will not work with my current Milq platform. If I can go away with 6.3V on filament then I will not be able to go away with 410V driving 10V. That would bring another B+ supply and so on. People have no idea how much I hate to do that DIY soldering crap! The second reason, probably the biggest one that for now I do not feel frustrated with the result I got from 2A3/RN604/YO186/45. My rules of the engagement no one cancels yet:

http://www.romythecat.com/Forums/ShowPost.aspx?PostID=432

cv wrote:

Anyway, whilst you do have the urge to experiment, you really, really should try a tapped filter choke at the front for gain adjustment instead of the attenuator at the S2.

This is a good one. I have a number of conversations with David about it. I do not exactly subscribe the idea of his tapped filter chokes and autoformers. In fact I feel that conceptually they are faulty. In regular resistive attenuator a signal flows across a resistor that is more of less free from any none-linearity. In a tapped chokes the attention happens via inductive resistance where the whole series signal flows across none-linear galvanic element. So, in theory I feel that restive attenuation is less devastating. I never used autoformers and frankly I have no motivations to do it. David, argues that a magnetic element is better than resistive and is willing to prove it to me by sending to me his speaker-level autoformers. I a very skeptical and I would rather to pay for a very high resolution (1/6dB) resistive speaker-level steps-attenuator with constant impedance. I am contemplating to commission the 16R LPAD if I find a right person….

cv wrote:

If it's not too much a departure from the subject of the thread, I'm a little surprised to see the back of the "Newton bias" scheme; does the 6E5p still retain its special qualities in this application with the more pedestrian bias arrangement here (IIRC the Newton scheme's primary benefits were at LF?), or might it now be worth experimenting with a filament-biased DHT at the front (and dropping some gain in the process...)?

Good point, I have thought about it as well. The 6E5P with "Newton Bias scheme” is not a panacea but a solution with well defined objective: to eliminate any explicit capacitor from a stage. How would you bias a tube? A buttery in grid or cathode do not sound right, not to mention that they are in a way the “capacitors”. A fix bias would imply a coupling cap or transformer, all versions of cathode bias would imply a cap in cathode. What you call the “Newton Bias” (actually the Newton Bias was another notion and it had nothing to do with Milq – that was a bias in Zaratustra amp) is affective way to bias with signal flows across juts a resistor – in my book the least damaging element. In the MF channel you see that I return to cathode bias but it was different. Since the objective was to lower the gain of my driver stage the 6E5P is use with no bypassing cathode cap –just a series resistor -means no negative problems in my book. 

Another point that I make is that I know how the 6E5P sounds with no caps and “Newton Bias”. I presume that it might be another application that might be fine but I would like do not spend time to evaluate many other options. In Milq tweeter channel of the “Newton Bias” on 6E5P in my view is not good idea at all as the 6E5P is quite capacitive bitch but what is the alternative? I have a single gain stage with a single resistor in a series signal path – what might be more kosher then this? I would like to have less capacitive tube with more gain and more power for HF channel, however….

cv wrote:

You might ask Dave if he knows of any 9-pin DHTs with mu of about 18 and Ri of about 1k... or have me send some old Limey tubes - begging your pardon, sire - valves to try...

I did ask about that type of tube before. Any interesting DHT candidates with high gain have too high plate impedance. If I find one that can do 20 times gain, have plate of 500R-700R and able to care 5W-7W on plate then I would go for one DHT stage. Unfortunately I do not know such a tube, with exception of high power transmitting tube that would run at 1kV and that I do not need.

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