[ARC5] Power Supplies for the ARC-5 Rx...and others.

[Kenneth G. Gordon]

On 29 Jan 2011 at 6:45, Military1944 at aol.com wrote:

> In a message dated 29/01/2011 05:06:28 GMT Standard Time,  
> vk2bcu at operamail.com writes:
> 
> I'm  dithering between a B+ supply value of 60 and 120 volts.  I don't
> think  90 to 120 volts stresses the set much, and it may work a little
> better at the  higher voltage.

In my experimenting on this matter, I determined that the receivers worked 
best at a voltage of between 160 and 180 VDC.

IMHO, 250 VDC is really too much, and not necessary even when the 
receivers were new.

Now.... I have mentioned this next in the past, but will reiterate it here for 
your benefit.

There was an article in one of the ham magazines some time ago, possibly 
as much as 30 years ago, in which the author, using a Drake 2B lowered the 
plate voltage in steps, while carefully documenting the results of careful tests 
during the procedure.

He found that the Drake 2B continued to operate just fine down to as low as 
12 VDC B+, although the audio output power was severely reduced at that 
point.

The most important of his findings was that internally generated noise was 
drastically reduced as he reduced the HV, and a small reduction in HV 
resulted in a much greater reduction in noise. In other words, the effect was 
not linear.

I distinctly remember some of his words: he said that at one point in his 
reduction series, he turned the receiver on, let it warm up and thought it was 
dead, as he could hear nothing at all on the 20 meter band....until he tuned 
in a signal, when that suddenly "popped up" to full clarity. The receiver noise 
was simply at such a low level he THOUGHT it was dead. It most certainly 
was not.

He finally raised the B+ back up to about 50 VDC and that is where he left it.

His contention (and others' I have read) was that receiver B+ was simply too 
high, having been chosen to be 250 VDC mainly because "that is the way we 
always did it." and it had become an industry standard for no really good 
technical reason, except perhaps for audio amp stage power output, and that 
with modern tubes and components, much lower voltages would be better.

Both National and Collins used voltages around 180 VDC in some of their 
later receivers.

Ken Gordon W7EKB