[ARC5] (1) Hacking Sets (2) Saving Sets

[Leslie Smith]

Hello ARC-5 list members:

There has been some discussion here about "hacking" the ARC-5 type command sets, and on a different but related subject preserving these sets. 

First, I would like to say "thank you" to list members in general and DS and MT (and his evil twin brother) in particular.  Here is the background to my "thank you".  Some time ago I got my grubby little hands on an R-24 (perhaps "a" R-24) receiver.  Remembering articles in QST I thought it would be a nice idea to "improve" the set by removing the valves, and building some jFET modules into (reclaimed) octal valve bases.  The idea was to keep the R-24 circuit (under chassis) intact, but solid state in the "toob" department.  In this way the set could be restored by swapping the solid state replacement and the original valves.   After some reading, a little correspondence and my involvement with this list I realised that this would result in a set whose performance was mediocre and at the same time "hacked" (and therefore of little value) if/when I decided to pass it on.    Consequently I have taken a different approach - I keep the sets operational by modifying them only where needed to keep them on the air.  (See note 1 below).  So - thank you DS and MT (and his evil brother).

As I write below, I document the few mods I make; these can be undone with little effort.  (Given that the sets I have acquired are common, I don't believe collectors will ever cast a greedy eye over them.)

Despite this, there is a point.  When I see how people react to my little collection of restored sets I'm certain they will be preserved - and rarer sets that I don't have too.  

Now to the subject of preseving sets on an island - Hawaii.  There is a memorial at Pearl Harbour.  Friends who have seen this tell me:  "You MUST visit the memorial at Pearl Harbour ..." etc.   

I have a question and a suggestion.  Q:  Knowing the history of Midway, and the part these sets played in the battle, would the museum at PH find a corner for a collection of these sets, with a note about their interesting history at Midway?  Would "Midway" or a corner for Midway be acceptable at PH?

With a little effort a recording of the actual history could go from one of the transmitters to a receiver on the other side of the room.  


I ask:  "How kewl is that?"

Michael:  I suggest a copy of your book would be must useful to the people who look after the display.  (Don't let your evil brother get his hands on your sets, or the manuscript.)

Keep up the good work!



Les Smith
formerly VK2BCU

Note #1.  This last week I pulled out a (slightly modified) BC-453 (nav. band) set.  The control box was missing, althought the box panel was in place.  A power switch, 6.5mm phone socket and RF gain pot had been mounted on the panel.   The problem I faced was common enough - there were 3 wires soldered to the genemotor plug AND two "holes" on the rear panel socket had been filled with solder.  (I use the rear panel socket for every connection to the set.  In this way I can take power and signals in/out without minimal modification.)  How could I get the solder out of the connector and off the 3 genemotor pins?  An interesting problem, yes?  A problem now solved.

Here is what I do to keep these sets restorable:   I note the following mods on paper which I put in a plastic pocket inside the valve box.  (0)  I use a PC card (described below) that replaces the genemotor, BFO on/off switch, and gives me an audio feed.  Plus a power on-off switch.  (1) I "snip" the single wire between the two 7k power resistors.  (This puts 45V on the screens, as distinct from about 25V with the divider in place.  25V is too low for reasonable gain.)  (2) I put a 33k resistor across the 150/330k plate dropping resistor for the triode of the 12K8.  (3) I parallel-tack a good bypass across the paper caps.  

I run my sets from a card that replaces the genemotor and provides 60V B+, 24V heater supply (AC, not DC) and BFO control.  For anyone interested in more detail:  LNSmith "at" OperaMail dot com.  

Returning to detail about the nav set I was repairing:  After a short time I had the set working.  It was working - 50% of these sets require no repair.   I will show the set to others at the local radio club (etc) and the result is always the same:  "gosh".  I cannot explain the interest in these sets, nor can I explain why I get indescribable satisfaction of hearing MCW ("WLM" or "RIC") from the local RAAF (air-force) base.  I'm certain that the sets I restore will be re-distibuted to other collectors in future years, and I'm sure they will be preserved.  I will build a 3 transistor (or more accurately 3jFET) mixer in front of this set and it will work as an 80m monitor.  Works really well.  Wonderfully stable.  Keeping these sets working is the secret to their on-going heritage.  Sometimes I build a nice polished wooden box that disguises the "military" look a little.  In this condition even women will accept them in the house.  All the men that see my sets say, "crikey!", where can I get one?  

I tap the side of my nose and say,  "Well, these sets are 60 years old.  They have real history.  They aren't easily got.  Even hacked up sets that work are hard to find."

This strategy means I can use the set, and it is a desirable aquisition.  It means that a following owner can restore the set if he wishes because he (or she) has the info necessary to do that.  

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