[ARC5] First AM QSO with the SCR-274!

[Mark K3MSB]

Congratulations!!    Your efforts are spurring me on to get my SCR-274N
going on AM.

2 Amps?   Are you using the meter on the antenna relay unit?   If so,  even
though it says "Antenna Current" the dial is not calibrated,  so a 2 is not
2 Amps.    I get about 2 on my 274N on 80M,  but using a T-19/T-22 I barely
get the needle moving, yet both give me about 40 to 50W output on CW.

For my 274N setup I use a 4:1 UNUN and an air-variable cap from old HT-37
transmitter with a few plates removed.    For the T-19/T-22 I just use a
series matching cap.   For 80M, the series C / roller inductance settings
are 200pf / 16, 100 pf / 28,  and 40pf / 24.

I did not hook up the side-tone;  I monitor my TX signal on the RX for
CW.    I may have to revisit that for AM.   Don't know.

"Portable Desk"!   I built my 274N so it would fit in the back of my Jeep,
the intent being to demo it at hamfests etc.   It's really not portable at
my age, more like luggable with the help of one of my boys getting it into
and out of the vehicle......

Again,  congrats OM.

73 Mark K3MSB


On Sun, Apr 16, 2017 at 9:46 PM, J Mcvey via ARC5 <arc5 at mailman.qth.net>
wrote:

> OK , the guy was only 40 miles away, but I'll take what I can get!
> He was familiar with the ARC radios and said it had the classic military
> audio.
> The mike I used has a carbon cartridge with the simple 'mike booster"
> circuit consisting of a transistor and 2.2k resistor.
> Haven't built my electret circuit into a mike yet, but I will get to it
> soon. The prototype worked well when I did a live test on the modulator. It
> has more amplitude/gain  than what I used today.
>
> It worked pretty well well with a 4:1 unun with a series cap to match the
> 80 meter dipole. Had to experimet with cap but I need about 150 pf on 80
> meters  ( it's on a junk box variable cap from a military tuning box, with
> the plates meshed, so I'll remeasure it to be sure) . Tried 100pf and 40 pf
> fixed caps, but couldn't get it to load with those.
> The power meter says it's a little over 50 watts on CW and maybe 12 watts
> carrier on AM.
>
> The inductor is happy at  around 1/3 around 3885.
> Interestingly, the current meter reads just under 2 amps on CW but the
> power meter says >50.
>
> I have not hooked up the sidetone/receive mute to the receiver rack and
> the feedback was very bad even with the sensitivity control all the way
> down.
> It was usable that way with CW, but not so much with AM!
> I'm wondering if the the grounding contact on the T/R relay might need
> some cleaning or is there really that much leakage into the receivers?
>
> After rewiring everything  into it's "portable radio desk", I'm glad it
> worked on the first try....
>
>
>
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