[ARC5] Receiver current drain

[Kenneth G. Gordon]

On 6 Jan 2011 at 6:22, J. Forster wrote:

> Hi Ken,
> 
> I'd be inclined to go a few volts higher on the diode string, so the
> Zeners are not turned on when the radio is operating.

Hello, John:

In these particular power supplies, there is enough series resistance in the 
filter system after the transformer that with any load beyond the Zener load, 
the output voltage will be lower than 250 VDC. 

For instance, with a load of 23 mA, the output voltage is 242 VDC.

Therefore, I figured that the only thing I needed the Zeners for is to clamp  
the unloaded 350 VDC to 250 VDC until the receiver load picks up, when 
they will "drop out".

I figured that doing it this way will almost perfectly emulate the original 
dynamotor power supply which outputs 250 VDC as soon as it comes up to 
speed and before the tube filaments warm up.

At 40 mA load, the output voltage of these power supplies is on the order of 
165 VDC.

I suppose I could adjust the series resistances (there are three of them) so 
that the Zeners would provide regulated 250 VDC output, but I am trying to 
keep this as simple as possible.

The transformers are capable of about 70 mA at least.

In my past experimentation with B+ voltage on ARC-5 receivers, the optimum 
seemed to be 180 VDC, so these power supplies will be just fine.

Thanks for the input. I very much appreciate the information I get here.

Ken W7EKB