[ARC5] Utility Amp Driving Advice.

[Bob Macklin]

DX-40s and DX-60s are quite common. Why not modify one of them to operate as 
a linear for the small radios.A Dx-60 should give you about 15W of AM 
carrier.

Bob Macklin
K5MYJ
Seattle, Wa.
"Real Radios Glow In The Dark"

----- Original Message ----- 
From: "David Stinson" <arc5 at ix.netcom.com>
To: <milsurplus at mailman.qth.net>; "ARC-5 List" <arc5 at mailman.qth.net>
Sent: Sunday, March 20, 2011 11:12 AM
Subject: [ARC5] Utility Amp Driving Advice.


> Many of my light-air radios output under five watts- some less than 2.
> They need a little boost on 75 mtr AM.
> I used a Motorola Triton 40S marine SSB rig as the heart
> of a utility linear amplifier.  Works well on the air
> on 160, 80, 40 and 30 mtrs (the rig is speced to 12 MC).
>
> Here's a couple of photos:
>
> http://home.netcom.com/~arc5/amp1.JPG
>
> http://home.netcom.com/~arc5/amp2.JPG
>
> I tapped into the driver input and brought-out
> the receiver antenna lead.  The rig is rated at 125 W PEP SSB.
> I cranked it back so that the unmodulated carrier is 40 watts,
> which is serviceable on good days and
> can drive a bigger amp if needed.
> RF envelope at the output while modulating
> looks excellent and reports are good.
>
> The drive level needed for full output
> is just 10 milliwatts into 50-ohms.
> I terminated the RF Input with a 50-ohm, 3 dB pad.
> I'm building a step-attenuator so I can drive it with
> anything from 7 watts (my SCR-288) down to
> sig-gen levels.
>
> I want to protect the input so I don't blow-up the driver.
> If I calculated correctly, 10 milliwatts in 50 ohms should
> be 1.414 Volts PTP.  If so, a simple set of four
> "up" and "down" ( or "left-n-right"  ;-)  silicon diodes-
> each leg with two in series to  to ground, which
> will forward bias at 1.4 volts and limit the input
> to 20 milliwatts, should do the trick.
> At lower drive levels, they should be "invisible."
> At high levels, they'll clip and distort.
> And when I screw-up and pop 40 watts into it,
> they should short and save my amp.
>
> First- did I get the math right?
> Second- what blatantly obvious thing am I missing?
>
> Thanks, Dave S.  AB5s
>
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