On Mar 1, 2005, at 9:08 AM, Vic Rosenthal wrote:
> R.Measures wrote:
>
>> In the AL-1500 diagram, the cathode is connected to one side of the
>> heater, C7 couples RF from the tuned-input to the cathode ,and C8
>> couples RF from the tuned-input to the other side of the heater. Can
>> someone please explain why the heater is driven with RF?
>
> I'm going to guess.
>
> The heater is connected to the cathode and isolated from ground by an
> RF choke because if it were grounded, then the heater-cathode capacity
> would reduce the drive available on the higher bands. Now, why
> connect BOTH sides of the heater to the drive?
A driver-powered heater? Now there's a new one.
>
> Let's suppose that C8 was removed. Then some of the drive would flow
> direct to the cathode,
If C8 were removed, C7 would couple all of the drive to the cathode.
> and some would flow into the heater and to the cathode and via the
> heater-cathode capacity. This portion of the drive signal might be
> modulated by the AC potential across the heater, adding an AM hum to
> the signal.
>
> Feeding both sides of the heater would tend to cancel the hum
> modulation.
>
> What do others think?
>
> --
> 73,
> Vic, K2VCO
> Fresno CA
> http://www.qsl.net/k2vco
>
>
>
Richard L. Measures, AG6K, 805.386.3734. www.somis.org
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