[ARC5] (no subject)

[Kenneth G. Gordon]

On 3 Sep 2010 at 1:29, Leslie Smith wrote:

> Hello Group:
> Yes, this is an interesting "one".  I don't know these sets well
> enough to know if the broadcast band sets came with a "loop" antenna
> selector.

Some did as far as I know. The receivers up through the 1.5 to 3.0 Mhz 
version were known as the Navigation Sets....at least according to my ARC-5 
manual.

>  I have a "navigation band" set (late WWII) with a "loop"
> antenna selector.  The setup is identical to what I see in the photo. 
> This is consistent with your observation about stencil showing 190 to
> 520kHz on the back panel.
> 
> Since all the IF transformers and the coil pack mount in sockets in,
> it's would be easy to believe these sets were made in a basic
> configuration (valves, tuning capacitor, wiring) and "configured" by
> simply by plugging in the correct coil box and IF transformers.  At
> least this is how I imagined the design concept at first.  I was
> always impressed by this concept.  Very clever.  Wrong, wrong, wrong,
> or at least not that simple.  Different sets in the same series (eg
> R-23 and R-26 from the ARA specification) have small components that
> are different.   For example, the local and BFO plate dropping
> resistors are not the same value across the range.  The lower
> frequency sets use higher value dropping resistors than the higher
> frequency sets.

Yes. And according to the ARC-5 manual I have here (I'll have to check the 
number and post here) there were other differences as well. AGC circuitry 
was different. Stability of the HF oscillator was changed in some of the later 
AN/ARC-5 models to enhance it, etc. Those higher-stability units, also known 
as "lock-tuned" (I think), had a yellow letter "S" inside a yellow circle stamped 
on the front panel.

>  I assume this is because the oscillators "take off"
> more readily at the lower frequency.

Dunno.

> Anyway, I digress from the set seen on "the bay".  Who-ever buys it
> will find one or two surprises not apparent from the photos, I'm
> certain.  For example, the dividing plate that separates the valve
> compartment from the tuning capacitor is missing.  This will make the
> set more prone to drift, because of the transfer of heat.

Possibly. With the covers on, and running on 250 VDC, those things get 
hotter than a $2 pistol. In an airplane at 20,000 feet and below zero, it 
probably HELPED stability. In a ham shack, all it does is burn up 
components.

In fact, as several folks here will tell you, the "ARC-5" receivers will work 
quite well with only 24 VDC as B+. I prefer about 170 VDC.

> O can't imagine why some-one would take the components from a rarer
> broadcast band set to modify a common "navigation" set.  

Possibly because just after WWII, MOST of the BC sets were fearfully torn to 
bits to make "Hi-Fi" broadcast tuners, whoever got this one used parts from 
such a torn-up BC set, or several sets, in order to attempt to make a useable 
one.

One of the major components I have seen missing from all the several 
versions of fearfully "modified" BC sets I own is the BFO transformer: those 
were routinely torn out and discarded.

Although I have a small collection of both IF cans and RF/OSC/MIXER 
tuning units for BC sets, I have NO BFO transformers. :-(

Ken Gordon W7EKB