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 Post subject: Drake TR-4c VFO
PostPosted: Sep Sun 19, 2021 7:32 pm 
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Joined: Sep Mon 06, 2021 6:18 pm
Posts: 7
My TR-4c is 50khz low VS Transmit frequency. Does anyone know off an adjustment to bring the two closer? I have set the dial to the transmit frequency but during QSO having to adjust receive when listening, Thanks


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 Post subject: Re: Drake TR-4c VFO
PostPosted: Sep Sun 19, 2021 8:37 pm 
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Joined: Jun Sun 19, 2011 2:31 pm
Posts: 8000
Is 50 Kilohertz perhaps a typo? That would be quite the trick for a TR-4 series because the same oscillators (BFO/Carrier, PTO, and Conversion) are used for transmit and receive. A problem with the voltage regulation to one of these could cause a slight shift because power supply voltage will vary between transmit and receive and if the circuit designed to provide stable voltage to the individual oscillators has a fault then a slight shift will occur but it shouldn't be anywhere close to 50 Khz. which would require multiple turns of the PTO dial.

If it is actually shifting 50 Khz., then I would suspect a major problem with the AC-4 power supply causing a voltage drop so severe that the regulators in the TR-4C oscillator circuits are dropping out of regulation by a huge degree.

With your TR-4C operating on either 80 or 20 meters, use an external receiver with BFO to listen to the TR-4C BFO/carrier oscillator (it is on 9 Mhz.) and the PTO (operates from 4.9-5.5 Mhz. depending upon where the PTO is tuned). For 10, 15, and 40 meter operation there is also a conversion oscillator used and it operates on selected crystal frequencies from 21.5 Mhz. to 43.6 Mhz. depending upon the selected band, the frequencies are shown on the schematic. Listening for a change in frequency of these oscillators between transmit and receive will identify the offending stage.

The PTO has its own regulation circuit, the BFO/carrier oscillator has regulated screen voltage via a VR tube in the set.

Rodger WQ9E


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