[ARC5] ARC-5 Issues

[Bill Cromwell]

Hi Chris,

Thanks for the review of all of that. I have looked at other overviews
of how the transmitters and receivers were controlled and keyed. I am
working to get a set of four "ARC-5" command receivers (mix n match)
into a home brewed "rack" along with four homebrewed (solid state)
transmitters, one for each of four bands. They'll cover 600, 160, 80,
and 40 meters. I intend for the control system to be similar. Whenever I
have looked at other overviews I missed one or two things and decided
that I would have to add the missing features to make it work right.
Your overview does include the features I decided were missing. You have
validated my own thinking. I'll be having a closer look at those
manuals. I think I already have copies on my PC.

Please be assured that the receivers I am using will NOT be butcherated
or ruinated any more than they already were before I got them. In some
areas they have already been or will be pushed closer to original.
Repairs have been made or are in the works. The 160 meter command
receiver seems pretty much unobtainium. Instead of butchering yet
another radio to cover that band a Q5er type converter will cover that
band nicely. Up front in direct line of sight will be four command
receivers in a row all dressed up in black. Whatever happens out of
sight behind them to make them function with their transmitters is
another thing entirely. That stuff does not require hacking the
receivers. Bathtub caps and out-of-spec resistors notwithstanding.

73,

Bill  KU8H



On Sun, 2013-02-24 at 07:47 -0800, Christopher Bowne wrote:
> Yes you are missing something.  In the original  design, K53 in the transmitter 
> is turned on by the transmitter selector switch in the little transmitter 
> control box. Each one of the 4 positions turns on K53 in an individual 
> transmitter....it stays on, while the K53s in any other transmitter in the 
> installed system stay off.  With K53 on , the cathodes of the finals are 
> returned to ground, and incoming  externally keyed B plus is lined up to be sent 
> to the MO and resonance indicator tube.  The final plates and screens do not get 
> their voltage via K53.  DC  power keying to all of the circuits are done by 
> relay K52 in the BC-456 modulator/dyno supply, a single contact makes and breaks 
> the 550V DC from the dyno that feeds the final  plates, the circuit that 
> develops the final screen voltage, and the  circuit that sends B plus to the K53 
> contact that sends B plus to the MO and resonance indicator tube. A seperate 
> antenna relay is also keyed in parallel with K52 and switches the antenna from 
> receiver to the transmitter(s).  All of the transmitters output terminals of an 
> installation  are wire in parallel, relay K54 in each transmitter is turned on 
> with K53 by the control box channel selector switch to connect the selected 
> transmitter's output to the antenna circuit.  Are you also keying K54 in the 
> transmitter, or did you just either jam the contacts closed or short around 
> them.  In  the original design, K53 and K54 in the transmitters were never 
> keyed, they just were turned on to select an individual transmitter from a group 
> of up to 4 of them.
> 
> Since you are using K53 as a keying relay, you are in fact making and breaking 
> the final cathode circuit.  With the contacts open, R75 limits the final plate 
> current on key up  so leaving the B plus on them and the screen may be OK on key 
> up, but I am not sure.  You should put a milliammmeter in series with the R75 
> cathode circuit to check how much current is being pulled, or you could check 
> the voltage developed across R75 on key up and do the ohms law math to figure 
> the current through it (and by extension the final plates).  But putting the 
> power on to the MO without going through K53 will give you that big backwave on 
> key up.
> 
> If I were you, I would try to keep the keying circuit as close to original as 
> possible, you will have no backwave issue and no issue with overheating the 
> finals.
> 
> 
> You should download the ARC-5 and SCR-274 N tech manuals from the BAMA web site, 
> they provide indepth discussion of the two systems.  The Handbook of Maintenance 
> Instructions provide the most info.