Re: uBitx v.4 build information
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73 de Rubens py2pvb
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Em ter., 7 de abr. de 2020 às 14:16, Evan Hand <elhandjr@...
Most likely it was heat that fried your finals. Digital modes have been reported to have this issue on all of the uBiTx models, as they keep the transmitter on for 15 seconds at a time at full power. Before going back on the air I would suggest that you add a fan, larger heatsinks, or both. Remember that the stock radio does not have electrical isolation of the heatsinks. Either keep the new heatsinks isolated, or add the insulators for the IRF510s. The alternative is to reduce the output power with the RV1 adjustment. I would adjust RV1 using an RF power meter and keep it under 10 watts for 40 meters. Monitor your finals temperature to verify that they are not getting too hot. As long as you can keep your finger on them right after the end of transmission, then they should be OK. I would send a continuous tune signal for at least 15 seconds into a dummy load, turn off the power and immediately check the finals. I did learn that if you do not turn off the power, there is a large risk that you will move the heatsink and short it out, usually just blowing the fuse.
As to how to set up the bias values for the new finals, there are instructions on the HF Signals and ubitx.net sights. I have used HF Signals for the bias adjustment:
You should not need to adjust the BFO or frequency calibration.
The above are just suggestions. There may be better ways to do the testing, however, the ones that I know of would require an IR measurement device.
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