[ARC5] Simple Question Arc-5 receiver power supply requirements?

[Kenneth G. Gordon]

On 4 Dec 2012 at 14:19, Bruce Long wrote:

> and ebay and build multiple different power supplies, I decided to do
> a clean design from the ground up using ordinary Mouser- Digikey type
> parts which will allow me to make several identical supplies. 

Good ideer...

> I thought the simple part would be to look up the voltage-current
> requirements but my efforts turned up a wide range of values.    The
> median seems to be 250vdc-80 mA and 28vdc - 400 mA obviously for
> receivers still wired for 28vdc filaments.

IMHO, that 80 mA is the capability of the dynamotor, not necessarily the requirement of the 
receiver. The current drain for the B+ is dependent on too many things, but mainly audio 
power output. I recently checked several receivers here which I am working on. The 
maximum B+ current drain at 250 VDC was 50 mA when both audio and RF gainis were set 
ot maximum. If you shoot for 80 mA, you will have ample reserve.
 
> I have also read of using less than 250 vdc to reduce the component voltage stress.  

I can absolutely attest to that: in my testing, I have found that 180 VDC is the absolute 
maximum that is actually "required". In point of fact, the receivers will work quite well at 
voltages down to 24 VDC, although at that low voltage, the audio power output is very low, 
and they take a long time to really warm up.

That 250 VDC was arrived at a LONG time ago, when tube operating-conditions were much 
different than they were even in WWII. Of course, if your receiver is operating in a noisy 
vibro-massage device at 30 angels and 30 below zero, 250 VDC would give you a margiin for 
error. For our uses, it is completely unnecessary.

> Filament voltage was of course dc in the original applications,  ham
> conversion generally used ac but I have seen some comments about
> returning to dc filament operation. 

In my experience, as long as the tubes exhibit no filament to cathode leakage, there is no 
reason to use DC on the filaments. The military used DC on the filaments because it was 
available.
 
> So what do you guys think is the ideal power supply operating
> specifications?  250vdc at 80 mA for the plates or something
> lower----28vac at 400 mA for the filaments or is there any practical
> reason to use dc?  Current specs listed above are actual expected
> receiver power supply currents with no power supply safety margin 

Go with an 80 mA current capability, but at lower voltage. I routinely use 180 VDC so I can 
use a 150 VDC VR tube for the HV when I use these receivers for monitoring: that seems to 
help a bit with stability.

Use 25.2 VAC or anything reasonably close, for filaments. However, the total filament current 
drain, if the receiver is NOT converted for 12.6 V filament voltage, is 3 X 150 mA or 450 mA, 
not 400 mA. All the tubes in the ARC-5 receivers draw 150 mA at 12.6 V. Since two tubes are 
in series across the 25.2 V DC line, they then draw 150 mA for every two tubes. That is 450 
mA, not 400 mA.

If the receiver is converted for 12.6 V filaments (all tubes in parallel) the total current drain is 
then 900 mA.

vy 73,

Ken W7EKB