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CAN SOMEONE EXSPLAIN DEMCO MODULATOR?

Stellasarat

Active Member
Sep 17, 2013
213
54
38
Ok. The modulator has a mic input located on the front panel. On the rear panel is a mic (male) wire. So my mic gets plugged into the front panel. Then I assume the male mic wire in the rear plugs into the radio. Am I right so far ? Ok. Now I assume it pointless to use this with a power mic. So how much better will a demco and unamplified d104 work compared to an amplified d104? And from what I've heard from others there's no comparison between an amplified d104 and an UN amplified d104 with a demco hooked up to it. I was told the Demco with the unamplified mic sounds much better. Why is this? Is it because the Demco is amplified useing tubes as opposed to the transistors used by the amplified 104. Everything I've said here is speculation on my part. I'm just trying to learn from people who have first hand knowledge of this type of modulator.
 

DEMCO POWER MODULATOR

STELLASARAT -

The Demco Power Modulator was an accessory used on early (1960s) tube-type radios sold by Browning, Demco, Sampson, and others. It is a tube-type SPEECH CLIPPER, and is a very effective way to increase average modulation (loudness). It is a 2 tube circuit, using a 12AU6 as an audio amp, and a 12AQ5 as a speech clipper. The front panel gain control allows you to adjust the output of the modulator to match your transceiver.
It requires a high impedance (50k-100kohms) microphone such as an unamplified D104 . Also, only use the modulator on rigs that require a high impedance mike!! Radios designed for low impedance mikes will load down the Demco's output, with the result being lousy-sounding audio. Hope this helps. 73s

- 399

DEMCO.png
 
Last edited:
DEMCO POWER MODULATOR

STELLASARAT -

The Demco Power Modulator was an accessory used on early (1960s) tube-type radios sold by Browning, Demco, Sampson, and others. It is a tube-type SPEECH CLIPPER, and is a very effective way to increase average modulation (loudness). It is a 2 tube circuit, using a 12AU6 as an audio amp, and a 12AQ5 as a speech clipper. The front panel gain control allows you to adjust the output of the modulator to match your transceiver.
It requires a high impedance (50k-100kohms) microphone such as an unamplified D104 . Also, only use the modulator on rigs that require a high impedance mike!! Radios designed for low impedance mikes will load down the Demco's output, with the result being lousy-sounding audio. Hope this helps. 73s

- 399

View attachment 12722
thanks for the info but i have another question my demco has no model number but is just like yours , Question to test it can i just turn it on and off and look at my output and see the gain or do i need a o scope to see this gain ? I have the fs 23 and the do104 nonamplied mic
thanks for any help
 
The Demco's had another wire as well. Their was a third wire and it allwowed you to hook it into IF stage and it feed back to the Modulator so that you would not over modulate even when clipping.You can set them up in circuit to do the same to your incoming audio and have it process that as weel.
 
If you have another radio laying around, hook it up to power an leave the antenna port open. Turn on the DEMCO, and see if you notice a difference in audio loudness. Easiest way to do it that I can think of without an oscilloscope.
 

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