[ARC5] Low B+ supplies for BC-454-B RX?

[Kenneth G. Gordon]

On 9 Apr 2006 at 14:34, Roger Basford wrote:

> I believe that it's quite feasible to run a BC-454, etc from a 50
> volts B+ supply, is this correct?

Yes. Quite correct. Many of us run them on 24 VDC to save having to 
replace those pesky can-type capacitors, especially C-16.

However, in my case, I have found that the voltage at which they exhibit 
NO differences in the way they operate is about 180 VDC. To me, that 
is their optimum operating voltage. In my case, I determined that the 
optimum voltage could be further reduced if one made modifications to 
the screen circuit voltage-divider, reducing the difference between 
screen voltage and plate voltage.

250 VDC is, IMHO, way too high and totally unnecessary. It stresses 
everything too much, and most of it is wasted as unnecessary heat. I, 
personally, don't think ANY receiver should be run on 250 VDC or 
higher.

In any case, our ARC-5s are no longer operating in a noisy, vibrating, 
refrigerator, in a near-vacuum.

There was an article published in an old CQ or 73 magazine about 30 
years ago that addressed the issue of running receivers on reduced 
voltage. The author used his Drake 2-B as the experimental subject. He 
found it would run quite acceptably on plate voltages as low as 12 VDC, 
although the audio output was way down of course.

The one thing he was most pleased to discover was that the receiver's 
noise floor dropped drastically as the voltage was reduced. I.e., a small 
reduction in plate voltage, made a much larger reduction in noise floor. 
In his case, he finally settled on a plate voltage of 70 VDC, IIRC, as the 
best compromise between audio output and everthing else.

So, your 50 V transformer should be just about perfect.

Ken Gordon W7EKB