Re: uBitx v.4 build information

Bill Cromwell

Hi Rubens,

Not to offend but things you mentioned as obvious are not obvious and not stated in your post. That RV1 controls the drive level though Q90 in my V3 (if I recall correctly) and in turn controls the finals. That transistor sets the drive level. Mine is currently dead. Yours may have been damaged when the finals and your meter were burned out. You did not mention looking there. That is the next place I would look. I have only just cleared my workbench of other people's radios and I will now replace that transistor in my own radio:)


Bill KU8H

On 4/16/20 11:29 AM, Rubens Kamimura wrote:
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@... <mailto:wrcromwell@...>> escreveu:
Did you reset the bias pots for the finals at the new voltage? You
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
> input, I used 20Vdc to power PA Power of uBITX v4, when adjusting
> 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@...>
>     <mailto:elhandjr@... <mailto:elhandjr@...>>>
>         Rubens,
>         Most likely it was heat that fried your finals.  Digital
>         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
>         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
>         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
>         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
bark less - wag more

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