I am a bit surprised that I did not get any response to my email about the
non-center-tapped filament in the HA14. The two 572B tubes have their
filaments wired in series one end of the string grounded and the other with
12.6 VAC applied. After thinking about it I realized that since the
amplifier is operating in a linear mode or class the 60 Hz signal and an
RF signal would simply be like an extreme two-tone test. The 60Hz would be
amplified but not pass thru to the antenna and the RF is amplified as
normal. Except for the intermodulation products due to the odd order terms
in the characteristic curves. And even that would be insignificant due to
the fact that the 60 Hz is so much smaller than the RF. So instead of
being 30db or so down as in a two tone test with equal level signals it
would be very much lower.
This would be like Grid Modulation in aClass C amplifier because the
second order terms would dominate producing 60 Hz upper and lower sidebands.
So, as long as you don't over drive the amplifier into non-linearity
there should be no 60 Hz sidebands (no 60 Hz modulation of carrier).
It would be interesting to put it to the test in some homebrew
amplifiers. Sometimes our long held assumptions get turned around and we
have to stop and think a bit.
73
Bill wa4lav
73
Bill wa4lav
At 12:35 PM 5/31/2005 -0400, Joe Giacobello wrote:
>Bill, I once used one for about a year. I never got any reports of a
>bad CW note nor did I detect any problem when I personally monitored the
>signal.
>
>73, Joe
>
>Bill Fuqua wrote:
>
> > To my surprise I found that the filaments of the HA-14 were not driven
> >by a center-tapped AC filament transformer when using the AC power supply.
> >I can see that this can be a real source of 60 Hz modulation on a
> >signal. Has anyone used these for CW using the AC power supply?
> >
> >73
> >Bill wa4lav
> >
> >_______________________________________________
> >Amps mailing list
> >Amps@contesting.com
> >http://lists.contesting.com/mailman/listinfo/amps
> >
> >
> >
>_______________________________________________
>Amps mailing list
>Amps@contesting.com
>http://lists.contesting.com/mailman/listinfo/amps
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|