[ARC5] running ARC-5 receiever fillaments on AC.

[Kenneth G. Gordon]

I run all my "ARC-5" receivers' filaments on AC and since I am very attentive to make my B+ 
as well-filtered as I can possibly make it, I have experienced no hum whatsoever from the 
filaments.

HOWEVER.....it is also true that if you want to achieve the maximum stability of which the 
receivers are capable (and they are remarkably stable), you MUST use REGULATED DC, 
or batteries, on the filaments. We have discovered that even the very slight rise and fall in 
the filament voltage caused by line-voltage variations can be easily seen when we use, say, 
the BC-453 on the MF "ham band" to monitor some of the high-stability signal modes used 
there.

On 26 Aug 2017 at 17:03, J Mcvey via ARC5 wrote:

> Thanks, The reason I ask is that I an old home-brew receiver power supply that 
> someone made.

OK.
 
> Now the next thing i discovered is that the transformer is probably under 
> -powered.
> It's a stancor PS-8416 125-0-125 @ 25ma.
> The rectified voltage may be sufficient but the current is probably too light?

That depends on what your B+ will be after the filter. At 250 VDC, the receivers use about 
50 mA of current when the gain control is at max and a signal is tuned it, but this is MUCH 
too loud.

If that power supply is using a full-wave rectifier like the 5Y3 or 6X4, then the output voltage 
will be on the order of 125 X 1.414, or about 176 VDC after the capacitor-input filter, not 
counting drop through the choke.

Let's assume your output voltage will be 175 VDC. That is 1/2 the 250 VDC. If the total load 
remains at 5000 ohms (250/0.05=5000), then at 175 VDC, the current SHOULD be 35 mA. I 
would think that at that voltage and current, your transformer SHOULD be OK.

If the rectifier is a 5Y3 or similar, you can reduce the load on the transformer a little bit by 
using solid-state diodes and not using the 5 V filament supply.

One simple, easily reversible, trick one can do to make the receivers work best at 175 VDC 
is to move the screen voltage feed from the junction of the two black resistors in the rear to 
the "hot" end, thereby running the screens at 175 VDC also. This makes a BIG 
improvement.

My experiments have shown me (at least) that the best voltage range to operate our 
receivers at is ~175 VDC, in fact.

If I have missed something, I am CERTAIN that someone here will correct me. ;-)

Ken W7EKB

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