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HR2510 Better Hi-Power
Modification
Increase the performance of this popular HF rig.
(Modification adapted from an article by Carl Merrill
73 Amateur Radio Today - April 1993, page 17)

The purpose of this modification is to make the 2SC2086 provide gain, for an emitter follower configuration, the gain is always less than 1. It works better, and saves the cost of adding an ECG-340(as stated in the "Beefing up the Uniden" mod).

The following modification will give you marked improvement in the output power of the HR2510 and is easy to implement:

1. Change the output from a MRF477 to a MRF497 and make the necessary bias adjustments as follows:

Connect the radio output to a 50 ohm dummy load and set the frequency to 28.005 MHz, USB mode, with no modulation.

Remove the shorting bar (PB-100) and hook up a DC Amp meter (0-100mA scale) between test points TP4 (+) and TP3 (-) to monitor final amplifier current.

Key the transmitter with no modulation and adjust VR112 for 80mA collector current (Q132).

Place the DC Amp meter's negative lead on TP2 and check the driver current.

Adjust VR113 for a driver current of 50mA, if necessary.

Replace the shorting bar (PB-100) into TP4, TP3 and TP2.

While tuned to 28MHz, adjust the AM power output to about 5 watts by adjusting VR107.

2. Turn off the power and locate Q134, the 2SC2086 amplifier transistor. Cut the foil, as shown on the the board layout diagram, to remove the network from the emitter. Remove the 0.01uF capacitor (C135) from the collector of this transistor to ground. Bridge the foil from the open end of the network to the collector foil. Now, solder the removed 0.01uF (C135) to the bottom of the board from the emitter to ground (across R167) See the diagram for details.

3. Check your work carefully for any mistakes or solder bridges and turn on the power. The AM power will normally jump up to about 15 watts after this modification. Turn the AM power output down to 12 or 13 watts by adjusting VR107.

This is plenty for this radio and will sound real nice on the air. You should find that the SSB power will now be around 25 to 32 watts.

4. Adjust SSB output for peak power by feeding a single 1 kHz tone (or dual tone) into the radio while adjusting VR104 (the SSB ALC control).

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