[ARC5] Power Supplies for the ARC-5 Rx...and others.

[Kenneth G. Gordon]

On 29 Jan 2011 at 16:20, David Stinson wrote:


> > As I remember it (this occurred some years ago) I tried regulated
> > 150 VDC with a view to increasing the stability of the receiver as
> > much as possible, but that did not work as well as raising the B+
> > above that point by several volts, to around 180 VDC.
> 
> I wonder why this would be?

I suspected at the time it was because the relationships of the various 
voltages and currents were "out of sync". I.e., lowering the plate voltage by, 
say, 50% lowers the screen voltage by, say, 75%...

If one adjusts the plate voltage, on which all other voltages are built, without 
ALSO adjusting the various resistances, the relationships of the various 
voltages go "out of sync".

Perhaps at some LOWER voltage, the synchrocity becomes better.

> When I run mine on 28 volts,  they are far more
> stable than at full voltage.

That is not what I meant: I didn't mean that it was more stable. What I meant 
was that it "worked better". I.e., operation seemed to be much more 
"normal".

> Is perhaps 180 volts the "sweet spot" for thermal inertia?
> And if so, perhaps a much lower voltage, like 28 volts is
> below the threshold where thermal inertia is a factor.

Possibly. However, when I tried to run my BC-453 at 28 volts, it became 
almost totally "deaf". Stability wasn't the question for me. The ARC-5 
receivers are stable enough for normal use over the 190 - 550 Khz range in 
stock condition. 

As far as enhancing stability is concerned, I was looking for maximum 
frequency stability since I intend to monitor the 500 Khz range of our 
operations for some very-high-stability digital modes. We are talking about 
+/- 3Hz over a definite period.

> IMHO, going all the way to 180 volts defeats
> the major reason to reduce B+: Preservation.

True, if that is what you are after, but I wasn't. I wanted to 1) reduce heat 
produced, 2) reduce to a minimum internally produced noise, 3) enhance 
stability by any means possible, 4) reduce stress on components.

I was experimenting with a receiver that although in stock configuration for 
the circuitry, had had all the can-caps replaced, among other things. In other 
words, it was already hacked, and was unrestorable.

> Caps that leak badly at 250 volts
> are going to leak badly at 180 volts.

True.

> At 28 volts, I rarely need to change even one cap,
> and when I do it's usually the audio cathode bypass.
> I recapped an RAT and that was a BIG mistake.
> Compared to my stock ones, it looks like crap.
> Forgive me; I was young ;).
> I am very willing to sacrifice performance for
> the sake of perservation.

I am too...IFF the receiver I am using is either restorable or has never been 
hacked. But what do YOU do with receivers that have been so terribly 
hacked that they are barely good only for parts, yet can still be made to work 
otherwise? Throw them away? Not me! I find a use for them.

>  If I want to work DX,
> I wouldn't do it with a BC-455.

Neither would I. For on thing, they are too broad.

> I have plastic radios for "performance."
> One doesn't enter a Ford Model "T" into a road race.
> The Model "T" is for slow, leasurely pleasure drives.

...or for racing, as is the case in Montana... :-) (and I am NOT kidding!)

Ken W7EKB