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GPA10 Assembly Phase 4: Output Amplifier

Components placement
Click Picture to Enlarge

Schematic diagram
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Remove temporary wires 1 and 2 and heatsink installed in previous phase.

Install SMT capacitor C7A.

Install components as shown below.

Install components as shown below.

Winding instructions for T1A and T2A:
Both transformers are identical. Start with winding 4 turns of the 0.5mm enamel wire as shown here.

Cut an 8cm length of RG174 coax cable. Remove 10mm of the outer jacket from one end. Pull out the centre conductor with its teflon insulation and discard. Finally, pass the shield and jacket once through each binocular hole as per photo.

Pull the conductors tight and solder.

This photo shows T1A and T2A installed.

Install TR1A and TR2A.

T1A and T2A Bias Adjustment:
It is very important that you make NO attempt at powering up the board without installation of a heatsink. Bias adjusting or transmitting without an adequate heatsink installed will cause permanent damage to the MOSFET. Furthermore, any adjustment during this stage must be done relatively quickly.

Adjustment Procedure:
1. Detach (remove) cables K1, K2 and K3.
2. Power up the board.
3. With trimmer pot RT2A, set the voltage at point TP6 to +4.30 V.
4. With trimmer pot RT1A, adjust the voltage at point TP7 to +4.30 V.
5. Turn off power to the GPA10.
6. Insert cable K1.
7. Turn power on.
8. Check the voltage at point TP6 and TP7. It should now read +0.05 V or less.
9. Power off.

This completes the adjustment of the bias voltage.

Solder temporary wire (3) at bottom of PCB, as per photo.

Connect a dummy load or resonant antenna and cables K1, K2 and K3. With 10mW drive from G59, you should be able to see around 15W of output on 40m band.

This completes assembly of phase 4.


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