erik2a3
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Regarding the choice of coupling capacitor: VCap or any capacitor can be used if the working voltage specifications and values are appropriate for the application. Mild caution is encouraged in the sense that this is an area that can become an area of too much concern, IMO and at least in my experience. Lots of builders, and something I've done myself, also experiment with the type of capacitor (as in oil or poly tubular type) used for the aforementioned input to filter capacitor, the first capacitor off the rectifier. Same goes for the cathode bias resistor bypass capacitor.
I want to just offer my opinion, which is of course nothing more than an opinion, that what I found so refreshing about this particular amplifier is that the circuit, which in my view is far more critical than the type or brand, rather, of passive parts used, is one that is not dependent on ultra expensive parts to provide, again in my opinion, extremely satisfactory performance. The most expensive cap in the world is going to do nothing for a compromised design, and in fact might it even worse. I tend to enjoy experimenting with some of the different tubes that can be used in the MT as a way of finding what works best for us -- and leave the basic circuit as it is. Certainly one should feel free to do other things if one is so inclined. If you don't have experience working with high voltage circuits, however, you MUST realize that the shock hazards posed can be extremely serious. I knew someone once who took this rather lightly and the following week got zapped terribly hard -- by an amplifier that wasn't even plugged in. The very heavy charge came from power supply reservoir capacitors in an amplifier that did not use a bleeder circuit, as it's called, on the output of the power supply. I remember how this felt, because the person was me. Be sure to measure the storage charge with a volt meter before doing ANYTHING. There are safe ways of releasing these dangerous voltages, which do NOT include simply shorting capacitors to ground. If you're not sure about what you're doing, don't take the chance and get help. Apologies, but I have to say this.....
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