[ARC5] Now - low voltage B+ on ARC-5 sets. (Was Arc-5 receiver power supply requirements?)

[Leslie Smith]

Hello Ken:

You wrote:  "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.

I'd like to add a comment to the "operate at 24v" observation.  In the
local oscillator and BFO plate circuit large value
resistors (eg 150k or more) drop the plate supply to a low value,
although I don't have the figure in my mind.
But it's certainly consistent with your "operate at 24V" observation.  

However, I routinely run "ARC-5" sets from a 60V B+ supply BUT to do
this I change the 2 dropping resistors and THEN the sets have (about)
24V on the plate.  However, the sets "starve" for plate current if the
resistor values are left original.  An interesting point here is that
the sets have the CORRECT voltage (according to the published figures in
the TM) but PLATE CURRENT must be maintained, not merely the stated
plate voltage.  So I figure the plate current (from voltage drop across
the plate resistor) and chose a value of plate dropping "R" to maintain
that current.  This is 15 .. 33k when B+ is 60 volts.

>Again, you wrote:  
> "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."
> 
I wonder, at times, why the "wisdom" at that time ran sets from 250
volts?  
The higher voltage places more stress on components, generates more heat
and noise.
I wonder if 250V was commonly used because "real men run 250V B+" and
"wimps run 90V B+".  I think 75 to 125V B+ seems fine, for a receiver. 
Not so effective on a 1625.

> > 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. 
> 
I find a small amount of hum running the sets with an AC supply.  This
disappears when I ground the chassis.

Vy 73

Les

PS - Ken some time ago you sent me your postal address (for a small
packet) and then I lost it when I had to do "things" to a disk.
Can you send it again, privately?  - Thanks.
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