Re: uBitx v.4 build information

Rubens Kamimura


Step Up (boost converter) arrived, so I get 20Vdc output from 13.8Vdc input, I used 20Vdc to power PA Power of uBITX v4, when adjusting the Ibias, the current went up at once reaching 15A , obviously damaged IRF510, PA Power plug, Ammeter ... I replaced the damaged components, so this time I installed a 0.34 Ohms power resistor (5W) in series with the step up output (20Vdc), but the output power is low, even with RV1 at maximum ... and C81 capacitor with 100nF, I only got about 8W.

What can I do now?


Rubens Kamimura .'.
Cel. (18) 9-9819-2225 WhatsApp ou (18) 9-9819-2255 

Em ter., 7 de abr. de 2020 às 15:44, Rubens Kamimura via <> escreveu:


Ok, tks.

73 de Rubens py2pvb 
Saudações fraternais, 73/51 PY2PVB

Rubens Kamimura
Tel. (18) 3746-8680 ramal 116
Cel. (18) 9-9819-2225 WhatsApp ou (18) 9-9819-2255 

Em ter., 7 de abr. de 2020 às 14:16, Evan Hand <elhandjr@...> escreveu:

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 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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