[Amps] AL-1500 Circuit Diagram

[R.Measures]

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