[ARC5] Replacement power xformer for a BC348 or other mil receivers

[Kenneth G. Gordon]

On 8 Aug 2022 at 13:37, JAMES FALLS wrote:

> 
> I built a dedicated variable LV PSU that tops out at 135VDC for use with a BC-342 and 314. Do 
> you think this could work for a `348? I want to give those old parts a break. I found the 342 to run 
> cool with only minor drift at LV between 90-120V. 
> 
> Jim Falls K6FWT

It has been my experience over a long period of time that lower B+ voltage for almost any 
receiver results in IMPROVED performance.

As I have mentioned here more than once, some time ago, someone tried reducing the B+ 
voltage to a Drake 2B receiver, just to see what the result was.

He discovered that the receiver worked just fine with lower voltages clear down to about +12 
VDC, except that AF output was much reduced at that level. RF/IF/Detector performance 
was NOT reduced. Overall receiver internal noise was MUCH reduced of course, as was 
heat, which reduced drift.

He finished his experiment by raising the B+ voltage to around +50 VDC and leaving it there.

As I remember it, the RAX series use a B+ voltage of around 180 VDC. 

In my experiments with "ARC-5" receivers, mine worked best at a plate voltage of around 170 
VDC although I had to raise the screen voltages to that point too in order to get maximum 
performance. Doing that involves moving one wire from the junction of the two big resistors in 
the rear of the receiver to the "hot" end.

I suppose, if AF output was an issue, one could run all of the receiver at the lower voltage, 
and use +250 V ONLY for the AF stage. I never felt the need to do that.

Ken W7EKB