> >As for distortion, I was thinking in terms of the Hi-Fi amplifier the one
> >person had. I'd try to do something to match the bias more evenly across
> >the filament, to not ruin the good sound that goes along with all that
> >cotton covered oxygen-free wire and those old clear sounding triodes.
> >
> In a push-pull stereo system, you MUST periodically swap the tubes
> around - left to right, push to pull - in order to even out the wear.
> Incorrect adjustment of the stereo balance can cause premature wear along
> the edges or centers of the anodes.
>
> 73 from Ian G3SEK
You also must after a few hours throw the tubes away, and get new
ones to maintain clear crisp warm audio sound. This even applies
to ham amplifiers according to one source.
Dave Ingram (K4TWJ) has written many articles about tubes in CQ
magazine. According to Dave, even 100 hours on a 3-500Z is too
long for that nice clean fresh tube-type sound so you should
replace the tubes. He actually did on-the-air comparisons that
confirmed this.
Dave claims you can't measure the difference, but you can hear it.
Just like changing the 100-odd PIN diodes in a radio won't change
anything you can measure, but the radio will just "sound" much
better. A fellow who makes that PIN mod explained that to me.
I really can't understand Hi Fi buffs using DC on the filaments of
directly heated tubes when it makes all but one area of the filament
incorrectly biased. At least they could return the cathode current to
the center of the DC supply so the middle of the filament was
correctly biased instead only one end. I'm amazed they can't hear
the distortion.
73, Tom W8JI
w8ji@contesting.com
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