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There is a big dividing line between AM-only and AM/SSB transmitters.

The sideband CBs have a circuit to "turn down" the carrier to the legal 4-Watt level. Whistle into the mike of a sideband radio. This is how much AM carrier it would try to deliver without a circuit to cut it back. Earliest 23-channel radios would just use a dropping resistor in line with the final's collector circuit. Most 40-channel radios had an adjustment, either a 15-Watt rheostat or a transistor circuit to drop the voltage.

Naturally a radio with the transistor carrier-set circuit is easiest to hijack as a carrier control. Some of them will 'swing' at any carrier level with only a simple mod. Other radios, like the 1978 TRC-457 RatShack model need extra persuasion.

AM-only transmitters are built to deliver that 4-Watt carrier and not much more. There is no need for the factory to include a control circuit, so if you want a carrier control, the entire control circuit and control both must be added.

Usual method is to reduce the collector-supply voltage to the driver only, using a capacitor to deliver full audio peaks with the steady DC voltage turned down.

Most common circuit uses a NPN Darlington power transistor between the modulated B+ and the driver transistor's collector choke. A Darlington transistor has a lot of gain, and reduces the current the control potentiometer must deliver to the transistor's base terminal.

Here's what we use.

73

<blockquote data-quote="nomadradio" data-source="post: 825078" data-attributes="member: 22">There is a big dividing line between AM-only and AM/SSB transmitters.The sideband CBs have a circuit to &quot;turn down&quot; the carrier to the legal 4-Watt level. Whistle into the mike of a sideband radio. This is how much AM carrier it would try to deliver without a circuit to cut it back. Earliest 23-channel radios would just use a dropping resistor in line with the final&#039;s collector circuit. Most 40-channel radios had an adjustment, either a 15-Watt rheostat or a transistor circuit to drop the voltage.Naturally a radio with the transistor carrier-set circuit is easiest to hijack as a carrier control. Some of them will &#039;swing&#039; at any carrier level with only a simple mod. Other radios, like the 1978 TRC-457 RatShack model need extra persuasion.AM-only transmitters are built to deliver that 4-Watt carrier and not much more. There is no need for the factory to include a control circuit, so if you want a carrier control, the entire control circuit and control both must be added.Usual method is to reduce the collector-supply voltage to the driver only, using a capacitor to deliver full audio peaks with the steady DC voltage turned down.Most common circuit uses a NPN Darlington power transistor between the modulated B+ and the driver transistor&#039;s collector choke. A Darlington transistor has a lot of gain, and reduces the current the control potentiometer must deliver to the transistor&#039;s base terminal.Here&#039;s what we use.<img src="https://imagizer.imageshack.com/img923/742/eDvUeI.jpg" alt="" class="fr-fic fr-dii fr-draggable " data-size="" style="" />73</blockquote>

[QUOTE="nomadradio, post: 825078, member: 22"] There is a big dividing line between AM-only and AM/SSB transmitters. The sideband CBs have a circuit to "turn down" the carrier to the legal 4-Watt level. Whistle into the mike of a sideband radio. This is how much AM carrier it would try to deliver without a circuit to cut it back. Earliest 23-channel radios would just use a dropping resistor in line with the final's collector circuit. Most 40-channel radios had an adjustment, either a 15-Watt rheostat or a transistor circuit to drop the voltage. Naturally a radio with the transistor carrier-set circuit is easiest to hijack as a carrier control. Some of them will 'swing' at any carrier level with only a simple mod. Other radios, like the 1978 TRC-457 RatShack model need extra persuasion. AM-only transmitters are built to deliver that 4-Watt carrier and not much more. There is no need for the factory to include a control circuit, so if you want a carrier control, the entire control circuit and control both must be added. Usual method is to reduce the collector-supply voltage to the driver only, using a capacitor to deliver full audio peaks with the steady DC voltage turned down. Most common circuit uses a NPN Darlington power transistor between the modulated B+ and the driver transistor's collector choke. A Darlington transistor has a lot of gain, and reduces the current the control potentiometer must deliver to the transistor's base terminal. Here's what we use. [IMG]https://imagizer.imageshack.com/img923/742/eDvUeI.jpg[/IMG] 73 [/QUOTE]

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