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The value/type of the capacitor after the gas tube hugely affects sound. I made quite a number of experiments in past with those caps and I have no idea why it is so. Well, I hardly understand (and I did not see anyone who does) why the “gassed resistor” biasing generality took the sound 6E5P way out the… So why should I understand WHY the value/type of small capacitor after the gas tube affects sound. However, it does affect it.

 If you look at the Melq’s circuit:

http://www.goodsoundclub.com/PDF/Melquiades_SET.pdf

then the cap C4 and C5 are very tricky sons of the bitches. Theoretically those caps should be irrelevant as they decupled form the tube grid by a large 390K resistor. Well, not so simple…

The circuit is very simple: a current regulating resistor, a gas tube with the following R10 and the cap across them. One of the cap’s legs sits with at the gas tube’s leg (it is critical). A gas tube creates own MF noise and the cap kills the noses. This is simple and very ordinary…

Now, I ran the amps with many different gas tube including the few versions of low current 5651 and I ran them… without C5 cap. No capacitor no problem other say – well, not so simple. Ironically when I did not use the C5 cap I did not have intolerable noise. I have some very minor MF noise that did not bother me at all. However, I did not have good sound either. The sound was vicious, erratic and reminded me a drunk driver driving. Applying, a small cap right across the tube itself (as it suggested in classic books) queried some noise but did not affect sound in necessary direction. However, placing the shunt cap after the R10 resistor did not necessary magic…

The value and type are other mysteries. 1uF, 2.2uF, 5uF did not sound properly. The 10uF for whatever reasons did. It was not that something got better or worse with raise of capacitance. The nose was killed at 2.2uF and further increase of capacitance did not affect anything… unit I reached 10uF. At 10uF is all come together making the 6E5P to sing in this application. I did true a good quality”expensive” plastic caps but it looks as “it” wants only electrolytic….

As I told before when I discovered this way to operate the 6E5P in Melquiades then was afraid to “loose sound” and did not go for anything further. Still, if a higher voltage gas regulator exists then it will be possible to use higher nominal of resistors to grid... It would always help, and particularly in the super Melq…. Sometimes in future, I plan to try two gas tubes at 300V. I do not know if pairing of the gas tubes will affects sound.  I also wonder if the increase the voltage will lead to the increase of the “best for sound” capacitor values after the gas tube…

Rgs,
Romy the Cat

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