michael w wrote:
This evening I finished another amp this time using a 6AW8A. For whatever reason the background noise is quieter than with the triodes. When I say "background noise" I'm referring to the normal sound being produced by just having the set turned on. I'm not referring to a noise that shouldn't be there like 60 cycle hum. Is there a better term for this besides what I'm calling it?
You mean background hiss from the radio?
I don't know what's going on because you've given literally no details at all, not the least of which is what OPTs you've used on each but bias, B+ voltage, circuit, gain, what radio, etc. are all missing. But, all else being equal, triodes don't have pentode screen-plate partition noise because they don't even have a screen. However, as I also said, that shouldn't even be detectable in the output tube so I can only conclude there's something else happening with the circuit configuration that's giving the false impression.
Ironically, 'noise' (if any) would be coming from the first stage gain triode and that's (I presume) a triode in ALL your little amps. Now PENTODE output amps have a rising frequency response due to speaker impedance (not so much with headphones), which would aggravate hiss, but you say it's the triodes. It just doesn't make sense. Just a wild stab in the dark, I suspect something OPT related, like core saturation, poor frequency response, or ?