Both voltage stabilisers 78L06 are to weak to handle the current demand and has to be replaced by a larger 1A type.If not , frequency shifting will occur on Rx and Tx.
The position of the 2 drivers on the tx board is wrongly printed , check EBC !
On the Rx board the IC is conected to the VFO output by a long path. At TX there is feedback into this lead and the frequency tends to shift. Cut the path as near as posible to the IC and make a coaxial conection to the TX board and the counter.
The bandwith of the receiver frontend is to narrow to cover the complete 20m band and needs to be modified according to this plan:
A bigger problem is the powertrain that tends to oscillate .
De-Qing the drviver stage takes care of the problem , place a 4K7-10K resistor over the first winding of TR as the plan shows:
 |
| Here's the correct way to wind the PA toroids: |
Tuning your antenna can be difficult without a MOX. Take great care by decoupling the wire to the resistor for it tends to pick up RF . This mod can also be used to perform cw on Taurus .
Audio is fairly weak in Taurus . Replacing the 100R at pin 6 of the IC by a 10R type is the option.
Changing from RX to TX can cause audio popping due to the discharging of the 100uF capacitor at pin 6 of the IC. Replacing the part bij a 10uF type cures the problem.
Audio is fairly weak in Taurus . Replacing the 100R at pin 6 of the IC by a 10R type is the option.
Changing from RX to TX can cause audio popping due to the discharging of the 100uF capacitor at pin 6 of the IC. Replacing the part bij a 10uF type cures the problem.
S-meter mod
Wim SP5DDJ wrote:
Here you have step by step alignment of VFO:
1. Set both 47k pots in the middle of its range. They will be used for range setting later
2. Set the multiturn pot in the left edge and check if you have minimum voltage on cathodes of varactors. This will result lower VFO frequency i.e.
4150kHz after alignment. If the left edge doesn't correspond to, change cables soldered to multipot.
3. Turn the VFO cap trimmer and find signal in RX or measure around 4150kHz.
4. Turning multipot to the right you should increase the frequency. Make a note what was the highest frequency in right edge of multipot.
5. Now is the time to set the span and both edges of VFO range. Use pots 47k and find out which is increasing or decreasing span and edge frequencies.
This is a very nice job to do and feel free to make some experiments. If the range is to low unwind one turn from VFO coil.
After alignment check voltages on varactor cathodes. You should have approx. 1V in one edge and 6V on the other side. Remember not to go below 1V in the left edge of multipot ( this is set by one of the 47k pots) because signal of VFO will be distorted. Make an exercise with this
About the oscillating PA stage he wrote:
1. Solder parallel resistor values between 1k to 10k to L5 ( driver circuit) pins 3 and 4
2. Change value of capacitor linking collector of 2N2219 with TR1 transformer pin 1. Try 10nF or less
3. Solder capacitor of 100pF between collector of 2SC2078 and ground on the bottom of PCB. Use shortest legs as possible
4. Parallel to first 2N3904 collector choke of 22uH solder 300 ohms resistor
Good luck and 73'ss
Wim SP5DDJ
Wim SP5DDJ wrote:
Here you have step by step alignment of VFO:
1. Set both 47k pots in the middle of its range. They will be used for range setting later
2. Set the multiturn pot in the left edge and check if you have minimum voltage on cathodes of varactors. This will result lower VFO frequency i.e.
4150kHz after alignment. If the left edge doesn't correspond to, change cables soldered to multipot.
3. Turn the VFO cap trimmer and find signal in RX or measure around 4150kHz.
4. Turning multipot to the right you should increase the frequency. Make a note what was the highest frequency in right edge of multipot.
5. Now is the time to set the span and both edges of VFO range. Use pots 47k and find out which is increasing or decreasing span and edge frequencies.
This is a very nice job to do and feel free to make some experiments. If the range is to low unwind one turn from VFO coil.
After alignment check voltages on varactor cathodes. You should have approx. 1V in one edge and 6V on the other side. Remember not to go below 1V in the left edge of multipot ( this is set by one of the 47k pots) because signal of VFO will be distorted. Make an exercise with this
About the oscillating PA stage he wrote:
1. Solder parallel resistor values between 1k to 10k to L5 ( driver circuit) pins 3 and 4
2. Change value of capacitor linking collector of 2N2219 with TR1 transformer pin 1. Try 10nF or less
3. Solder capacitor of 100pF between collector of 2SC2078 and ground on the bottom of PCB. Use shortest legs as possible
4. Parallel to first 2N3904 collector choke of 22uH solder 300 ohms resistor
Good luck and 73'ss
Wim SP5DDJ
