[ARC5] Receiver Power Supply

[Kenneth G. Gordon]

On 28 Apr 2015 at 13:36, D C _Mac_ Macdonald wrote:

> I believe some folks here on the ARC-5 list, recommend keeping the B+ voltage
> down around 175V or lower to ease stress on the old capacitors in the receivers.
>  Using a choke input filter setup with this transformer should probably get you
> into that "safe" territory at a minor cost in audio output power. 

In my tests on receiver plate voltage, I have found that in several cases, the 
"best" voltage was "about" 170 VDC or so, although that is most certainly not 
a "hard and fast" figure either. It seemed to vary a bit between receivers.

At that voltage, receiver noise appeared to be noticeably lower, heat 
produced was reduced, and yet audio output power appeared to be 
uneffected.

This had nothing to do with the capacitors, since I had changed all those out 
as most were completely shorted in the receivers on which I was working at 
the time.

However, with 170 VDC as HV, the screen voltage had to be increased to 
the same level by moving the tap at the center of the screen voltage divider 
to the input side.

Unless one did this, the receiver sensistivity was low, and it took a long time 
to warm up to proper stability.

Heat reduction was dramatic, though.

If one wished to use a voltage-regulated power supply (which does have 
some advantages in short-term drift), and since I really like VR tubes, mainly 
due to their pretty colors, a VR-105 in series with a VR-75 provides exaxtly 
180 VDC.

Ken W7EKB