[Amps] AL-1500 Circuit Diagram

[Vic Rosenthal]

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?

Let's suppose that C8 was removed.  Then some of the drive would flow direct 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