In Reply to: Re: When was the Moondog first made? Cap value confusion posted by mobile homeless on December 26, 2000 at 11:51:00:
Just a note on coupling caps. As you are probably aware, the coupling cap is used to stop DC voltage from passing from one gain stage to the next. The value of the cap is like a crossover point in a loudspeaker. The higher the value of the cap, the lower the crossover point. A 1uf to a 5uf cap will yield a crossover points down to around 5hz. These higher value caps are typically used only in pre-amps. A 0.22uf cap will allow for around 20hz. The reason that coupling caps in amps are not in the 1uf to 5uf range is for stability of the output stage.You can pretty much use any value from between 0.68uf and 0.10uf for an interstage coupling cap and be just fine sonically. The output transformer has a limiting effect on the low frequency output, and so does the output tube. After about 0.33uf you typically will not measure much better frequency response. Going above 1uf and you possibly watch your output tube get funky. Sometimes cap values smaller than 0.10 can be used if your speakers have a frequency response only down to 40hz to 50hz, your amp will not waste precious energy producing frequencies your speaker cannot reproduce. The result will be greater perceived power.
Which type of cap to use? That is where this stuff gets fun. If you are a POGE like me, using paper in oils, silver Teflon, non-polar electrolytic, poly props, or anything else you can dig up will have a unique and harmless impact on the sound. (A lot less dangerous than changing types or bias points and plate supply voltages on driver tubes). The impact on the sound of cap type selection is often much greater than the brand of tube you are using, (unless you like to use really, really crappy tubes). Keep within the design parameters and you can cause no (major) harm.
The thing to keep in mind when using brand new paper in oils. They take a long time to break in, 100 hours or so. They can sound really bad during the break in period. Don't give up on them. Once in their groove they are not as colored or opaque, as some would have you believe.
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