[ARC5] BC-459

[Christopher Bowne]

Re matching the Command set transmitters to 50 ohm loads, I use a tuned parallel LC network autotransformer described in one of Walt Hutchen’s Electric Radio in Uniform columns in the late 1980s. Mad my coil from an Eico 720 transmitter pi network coil and used a shorting jumper to allow it to resonate on 80 and 40 meters.  IIRC the coax antenna feed line was tapped about 6 turns from the grounded bottom and of the coil.  The output of the transmitter was fed through a 100 pf series cap to a tap about 3 turns from the bottom of the coil. One has to resonate both the series loading coil in the transmitter and the parallel LC autotransformer.  For the autotransformer cap I use one of the ARC 5 transmitter variables removed from a hanger queen parts car.  I could easily obtain 50 watts out of my Command Set transmitters with the nominal 550 volts provided from the DM-8 dynamotor on a BC-456 screen modulator and about 20 watts on AM.  One trick of the trade to get the best modulation from a screen modulated transmitter with the BC-456 is to tune for maximum output in CW and then shift the operating mode to voice.   Many of the command set transmitters have a caution plate to that effect on thier front panels.

Chris AJ1G 
Stonington CT
Sent from my iPhone

> On Feb 27, 2025, at 14:42, howard holden <holden7471 at msn.com> wrote:
> 
> I have an ATA CBY52208 and a BC-458A. I use a 500pF variable ACROSS the output, and I match 50 ohms pretty well, a dipole on 80 and a true EFHW on 40. The variable enables me to match both the ATA (80M) and the BC-458A (40M) quite well, below 1.5 SWR. I get 35-45 watts out of both with 520V on the plates, 200 on the screens, and 150 on the oscillator. The variable coil tap is on the about 2 turns from the left side of the window.
> 
> 73, Howie WB2AWQ
> 
> ________________________________________
> From: arc5-bounces at mailman.qth.net on behalf of sbjohnston--- via ARC5
> Sent: Thursday, February 27, 2025 11:26 AM
> To: arc5 at mailman.qth.net
> Subject: Re: [ARC5] BC-459
> 
>> command radios were designed to run on short antennasThe ARC-5 transmitter's short antenna design can be handy in certain situations, such the time I was in a temporary location and strung a relatively short wire out the window to a nearby tree.  With a chassis connection to the household ground it worked well.  I'm sure some Novices did the same back in the day.  If I intend to drive a 50 ohm resistive load, I added a series capacitor on the output (transmitting type usually, but I have also used a heavy-duty, high-voltage ceramic disk capacitor).  Then the rig thinks it is still looking into a capacitive load and transfers power efficiently.  I believe the rotary inductor ends up close to the bottom of its travel.On the rig under discussion, since it already had been modified with an SO-239 on the front, I installed the series capacitor inside, behind the front panel, in the line running to the center of the coaxial jack.  I think the value was 50 pF.Steve WD8DAS   sbjohnston at aol.com   http://www.wd8das.net/   http://af4k-crystals.com/   --------------------------------------------------------------------   Radio is your best entertainment value.   --------------------------------------------------------------------   Mein Ohr ganz nah am Weltempfänger...
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