[Milsurplus] 24V B+

[David Stinson]

----- Original Message ----- 
From: "Ray Fantini" <RAFANTINI at salisbury.edu>
To: "David Stinson" <arc5 at ix.netcom.com>; <milsurplus at mailman.qth.net>
Subject: Re: [Milsurplus] Low B+: The Genius of A.R.C.

> Not being critical because I have not done the work myself and have
> no experience using octal remote cutoff pentodes at low voltages
> but have to wonder why other then the convenience of having
>24 or 28 volts there why you use such a low voltage? ...

Thanks for writing, Ray.
No offense taken at all, good sir!
I'm glad to be invited to discuss it.
There are several issues and I hope our readers will be patient
while I make the case for B+ at this low level.
All that follows is, of course, IMHO and YMMV ;-).

Now, this concerns only certain sets, including the "ARC-5"
types. Some sets do require more than 24 Volts.
The Australian AR8 needs at least 45 volts,
while the DU-1 DFer works fine all the way down to 12.
For this discussion, I'll stick to just the ARC-5 and other
sets that will work at 24 Volts.

I'm a fairly pragmatic person; for me,
this is a "benefit vs. cost" calculation.
Performance is not my first priority.
In fact, it's far down the list.
I can either make some contacts with friends
on 40 or 80 meters or I can't.
"Performance" beyond this personal standard is not an issue.

I believe that, in a word of radios like
the Kenwood TH-F6-AT, even attempting to maximize
"performance" from 80-year-old technology is folly;
it's like bringing a horse and buggy to a NASCAR race.
No matter how "good" the buggy is, or how well
you tweek it- if you came to race, you're already dead.
The wiser course is to crank back on the ambitions
one has for that 80-year-old buggy, relax and go
for an easy, sunny ride in the country that doesn't
strain the horse so much. There are joys in a
nice, slow ride in a buggy you brought back
into service by your own sweat.
Attemping to "race" it will tear it up
and make you look bad.

I leave performance to the "plastic" radios.
If I want to QSO some rare DX or roast birds on the wing,
I'll use one of those Yea-Com-Woodie boxes that look like
they were built out of LEGO blocks.
I work with WWII radios because I honor their history,
I admire their design within the context of their age,
and because it's challenging to get them running
while respecting their integrity as historic artifacts.
I'm not interested in "noise figures" or "efficiency"
or "operating points" or any of that.
All it takes to get all of that stuff you want is money.
If a fella has the dough, he can buy a rig
that will give him "performance."

That being said: here is my "benefit vs. cost" analysis
for using 24-28 volts for B+:

Benefits:
1. Componant and Set preservation.
Many (most) caps that leak awfully at 200 volts
work just fine at 28 volts.
Even if they do leak, it's micro (or pico) amps.
With only 24 volts B+, a leaky grid coupling cap
doesn't leak enough to mung the following stage bias.
Screen dropping resistors that would have
been roasted don't get warm.
Even when resistors have gone way out of tolerance,
the sets usually function. The lower the B+,
the less strain and the less leakage
2. Minimizes "surgery." In most cases, I need only replace
caps that are flat short or nearly so, and only resistors
that have gone totally "off the reservation"
(i.e. a 500K that's at 3 megs, or a 1 meg at 12).
De-Ox-it the switches/pots/rollers, lube where needed,
check the tubes, then put the juice to it.
Nine times out of ten the set comes right up without trouble.
If there is a big problem, the low B+ prevents major damage.
3. Economy and Simplicity. A single power supply is easy.
If I'm going to build a second supply for 60 or 90V B+,
I haven't saved anything. Might as well build a 250V.
4. Encouragement for Newbies. We need to encourage
new people to investigate our sets and build an interest.
The simpler it is for them to actually get some noise out
of a set, the more likely they are to try it. They can get a
24 Volt, two Amp supply out of a wall wart these days.
Building a 200 V+ supply to go with it is more than most
newbies wish to tackle early-on. And it's dangerous for them,
leading to:
5. Safety. I'm not getting younger. I'm getting older, clumsier
and forgetful. Sorry, but so are you. I work on gear powered at
12, 24 and 48 volts all day long. I can prod, finger-poke and
fiddle with that stuff all day and about all that will happen is
an occasional tickle. It gets to be habit to look for intermits
by pushing here and poking there. When it's not 24
but 600 Volts you're poking, that "senior moment"
can kill you worm-chow dead.

I'm sure there are others, but these are enough.

Costs:
1. Reduced, but still acceptable, performance.
2. Need an inexpensive amplified speaker.
I can buy one new at Frys for ten bucks,
or find one at a yard sale for 50-cents.

That's it. I can't think of any other disadvantage of 24 Volts B+
vs. any higher voltage in these sets.

For me, the advantages to 24V B+ are clear
and the argument from "performance" is irrelevant.
Others may feel challenged to get the "best" performance
they can from their horse and buggy, and Godspeed to them.
I think it's a bootless errand, but "whatever floats ya boat" ;-).

Thanks for putting-up with my blow-veation, Ray.

73 OM DE Dave AB5S