|Aligning the Hardrock 50 revisited
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|Author:||nm5ps [ Sun Aug 26, 2018 11:44 pm ]|
|Post subject:||Aligning the Hardrock 50 revisited|
I've just finished the build on my Hardrock 50 and have run into an issue during alignment. Essentially, I get no current readings on VR1 during the last page's adjustments. The resistance checks all were fine. After cranking back the resisters by about 40 full turns each, resistance at the gates of all four power transistors ranged from 51.4 ohms to 51.7 ohms. And I could see as I turned the set screws counterclockwise that the resistance was dropping.
I connected the test leads (1-4) and used a shorted female RCA plug on the PTT jack as lead 5. When I powered up the amp, it passed the smoke test with flying colors. I had set the band to 30m and the mode to PTT.
With power applied I turned VR1's screw clockwise well beyond the 40 turns needed to drop the resistance to within 40-60 ohms. No joy. The resistance was well above the 333 ohms another builder measured on VR1 on his amp back in March(?) as he tried to troubleshoot problems getting current readings on VR3 and 4. After reading that exchange, I checked the fuses in my DMM. Both are fine. I double-checked the test leads I was using to make sure none were flaky. The were fine. I repeated the test-lead connection sequence to make sure I hadn't missed anything. I hadn't. Voltage on the drains of V1-4 all read 13.4 VDC, matching the power supply's output voltage.
Next troubleshooting step?
I'm looking forward to getting this puppy on the air.
With best regards,
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