Re: uBitx v.4 build information

Rubens Kamimura


Thanks for answering me!
Obviously, I fulfilled the ritual to the letter, as I have been in the maintenance area for over 45 years.
With reference to the voltage gradient of the converter booster (stepup) convert, at empty we have 20Vcc adjusted in the multiturn trimmer and in TX, obviously the voltage drops (dropped to 19.98Vcc). So I found it strange 20.00 - 19.98 = 0.02Vdc, and as V = R x I, considering R = 0.34 ohms and V = 20Vdc, we would have a current of approximately 588.24mA, ignoring losses. We have something strange ... 588mA - 200mA = 388mA (current in TX, discounted Ibias).


Rubens Kamimura
Cel.+55 (18) 9-9819-2225 WhatsApp ou (18) 9-9819-2255 

Em qui., 16 de abr. de 2020 às 12:11, Bill Cromwell <wrcromwell@...> escreveu:


Did you reset the bias pots for the finals at the new voltage? You would
have to set them to minimum (full clockwise) and then apply power. Go
through the whole procedure for setting the bias with the 20 volts
applied instead of the previous 12 volts.

Can your buck/boost gizmo supply enough current. Twenty volts with no
load drops to what voltage when transmitting (measured at the radio)?


Bill  KU8H

On 4/16/20 10:40 AM, Rubens Kamimura wrote:
> All
> 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?
> 73 PY2PVB
> 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:
>     Evan,
>     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@...
>     <mailto:elhandjr@...>> escreveu:
>         Rubens,
>         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.
>         73
>         Evan
>         AC9TU

bark less - wag more

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