Super Tuna assembly is now essentially complete and I am entering the tweaking and troubleshooting stage. I built the 30M Band Module first do to that band being more open during daylight hours in the winter, especially when picnic table operation early morning or at dinner time involves dealing with herds of the Florida state bird flocks that carry you away unless you are walking at battlespeed.
- Initial power-up revealed the Red LED cycled perfectly during straight key closes. Good, the keying circuit is working.
- Tuning in on my receiver on the table, I found the signal at 10.11454 MHz with the VXO turned to the extreme left limit. I am using a 10.116 MHz crystal.
- Turning the VXO to the extreme right limit, the signal moved to 10.14655 MHz. That is a nice 3 KHz range and the XVO tunes as smooth and as linear as a VFO.
- In my book, this meant transformer T1 Primary was connected and functioning with the oscillator doing exactly what it should be doing. The waveform sounded crisp and stable with a high chance the component values were correct and soldered correctly.
- I then installed the final Q3 transistor into its socket and added its heatsink. The sound in the receiver did not change, but the RF Probe circuit does not register a voltage, the final amplifier Q3 isn't switching perhaps. I traced the circuit back from the RF Probe (Peak-n-Hold circuit) to the collector of Q3 and everything appears to be correct, including the bandpass filter (which has no immediate bearing on Q3 turning on). At this point I verified the Transformer T1 again, the windings are correct, 25T Primary & 5T Secondary. My T1 is 90 deg turned from the instructions due to the direction I wound the first turn, but all subsequent turns followed the same pattern to use as minimal wire as possible and no soldered wires crossing each other. Primary & Secondary wires are soldered in the correct solder pads.
- Next step: I added solder tinning to the transistor legs as they fit too loose in the 3 pins for my comfort. I tried several 2N3866 transistors with no change in action. Zener ZD1 is the correct part as well as all resistors and caps.? I wondered if adding solder to the legs to tin the transistor legs risked ESD failure. I have not yet replaced the 3-pins soldered into the board that forms a socket, I have nothing in the junk box that will work better.
- Later today I will take more measurements with the RF Probe to gain some more data for comparison.
Notes: There are two Q3 transistors on the schematic, the one in the Keying Circuit is actually Q4. The R10 on the schematic current limiting the Red LED is actually R11 and R10 is assigned to be a current limiting resistor for the optional LED that would iluminate the PWR and FUN trim pots (LED not installed here). If measured voltages at the Base of Q3 are insufficient to turn it on, I will try rewinding although the form looks very ideal. Winding it for T1 to be turned 90 deg should not affect BE Voltage measurements in any way. If BE Voltage measurements are good, I may try lifting ZD1 as it could be clamping too low although it does not show as being shorted either.
Back to the fun after a walk with the wife ...
Davey - KU9L
David Knapp