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RE: G2 regulator for SE EL84 amp

Posted by Alex Kitic (A) on July 16, 2015 at 02:09:01

In Reply to: RE: G2 regulator for SE EL84 amp posted by DAK on July 16, 2015 at 01:27:57:

"when I use the zener to set the G2 voltage, I can hear a little hardness in the sound quality. I notice that after about a half hour my ears start to ache a little. This character is not with the rh84 with a resistor used to drop the G2 voltage. So, even if the noise is many hertz above the human hearing range it still can be sensed."

I have not noticed this effect, in my view the "stiffer guidance" of g2 voltage by means setting a difference in potential between B+ and g2, as compared to a resistor dropping voltage as a function of g2 current draw, leads to improved precision and speed, particularly with bass notes - with no adverse effects elsewhere in the audio spectrum.

I have run across remarks how "regulating" the g2 voltage by means of using zener diodes instead of resistors decreases distortion, which might be possible to explain as a side-effect of the above.

While g2 can be used to drive a pentode (instead of using g1) the amplification factor for such use is way lower. Therefore noise introduced via g2 can hardly be detected by instruments at the output, let alone heard against the audio signal introduced via g1.

Besides, I don't think that zener noise (which is a typical armchair-DIY thing, i.e. something that can be shown on a graph or as a result, but has little or no effect on real-life applications, either due to being irrelevant per-se, or being heavily masked by a whole lot of other signals and noise(s) involved in the real task of the amplifier - which should be music reproduction) has anything to do with the symptoms you are mentioning.

If you are looking for a zener diode replacement, I guess the smaller cold-cathode regulator tubes like 0A2, 0B2 and similar could be used as a series-pass device. The drawback is represented by the limited choice of values (75-105-150 V, mostly) and current draw limitations. Even the EL84's g2 draws at least 5mA, and you can obviously connect all g2s together (as it has no effect on the outcome, being just a voltage reference which is not in the same signal or AC path with the anode). The cold-cathode regulator tubes generate more noise than zener diodes, but the noise is different. Nevertheless, you should not be able to hear any noise being introduced via g2.


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