Lafayette Telsat SSB 140 TX Offset?

[Lkaskel]

Hi Gang,
I have on the bench a Telsat SSB 140. The oscillator alignment is perfect but the radio is not transmitting on frequency. There is not a TX offset so I am curious how you match the TX frequency with the receive? The clarifier is not unlocked. Any thoughts? I have checked other Cybernet radios like the GE 3-5825A and Telsat SSB 120 and they are the same setup.

All the best!!!

 

[nomadradio]

No transmit-side trimpot for that radio. Transmit-side (only) tuning voltage to the clarifier-circuit varactor diode comes from two fixed resistors R25 and R26.

This is one reason we routinely unlock the clarifier on this radio. I'm accustomed to soldering a low-power 3-terminal regulator 78L08 across the clarifier control's outer two lugs, and powering the regulator with a wire leading back to the main filter cap on the main pc board.

After pulling D5 and R24.

Another approach is to set the trimmer caps CT4 and CT5 on transmit for correct channel frequency. Then pull the knob off the front-panel clarifier control. Now turn the shaft of the clarifier so the receiver's frequency agrees with the transmit frequency. Push the knob back on the clarifier control with the pointer at 12 o'clock. This will give you a stock setup with the receiver on nearly the same frequency as transmit with the clarifier knob centered.

Easier than trying to shoehorn a transmit-frequency trimpot in place of R25/R26.

73

 

[loosecannon]

just to add to the good info, here is a link to a service manual that contains the circuit theory.

this radio is the same as your lafayette on the inside:
http://www.cbtricks.com/radios/hygain/hygain_5_2705/index.htm

LC