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I have a SBITX V2 and have had no issues at all with it.? I believe the only difference between the V3 and V2 board is a different MOSFET used in the PA and some supporting components.? But I’m unable to confirm that.? There’s no need for met to “upgrade” based on a different PA.? Is there something I’m missing?? I was hoping to see two different schematics that I could compare but have come up empty-handed. ? Can anyone confirm the differences between the V2 and V3 SBITX boards? ? I’ll probably update to the V3 software this week, after making a good backup of my SD card. ? Steve Barkes W5RRX ?
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H Steve, The PA stages are the only real difference.? One addition to the production units (at least the one sent to me) I have not seen on any schematic is the TVS gate protection that is very much needed on the V2 circuit with the IRFZ24N finals.? Gordon Gibby has had issues with his V2 around the HV doubler and the T/R switching circuit around Q9 and Q101.? I implemented a different solution to the T/R switch and plan to add the series resistor to protect the voltage-doubling circuit diodes. The IRF510 circuit seems to be more stable, so unless I see a lot of issues with it here in the group, I do not plan on implementing the mods. As I stated in response to a request from Jens, I am happy with the hardware.? The software still needs work. /g/BITX20/message/10738573 Evan AC9TU
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Protection resistors need to be added to the drain of Q101 ?(suggest 150 to 200 ohms) & to the two diode’s going to the TR circuit from +12. ? (suggest 470 ohms) In both cases, momentary high currents destroy semiconductors because there were no current limiting resistors. ?In the case of the Q101 switch it is almost a guaranteed eventuality,in the case of The two diodes, I don’t know how it happened but any boo-boo with a test probe could cause it There may be other portions of the circuit that need to be made a bit more hardened. Those are just the two that I have blundered ?into so far! ?
I have been impressed with the quality of the low pass filtering, but not so much with the vulnerability of specific parts of circuits. ? Since ham radio operators are usually given the right to repair their own equipment, providing some level of idiot proofing is a good idea. ? ? For example apparently there is now a diode across the power supply input leads. ? And a fuse was in the power cable that came with the used unit that I bought. ?
Fixing these vulnerabilities will in the long run reduce the complaints that the manufacturer eventually has to deal with. Not everybody is brilliant and we can all make mistakes! ?Been there, done that ??
Gordon Kx4z?
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On Jan 2, 2024, at 17:08, Evan Hand <elhandjr@...> wrote:
?H Steve, The PA stages are the only real difference.? One addition to the production units (at least the one sent to me) I have not seen on any schematic is the TVS gate protection that is very much needed on the V2 circuit with the IRFZ24N finals.? Gordon Gibby has had issues with his V2 around the HV doubler and the T/R switching circuit around Q9 and Q101.? I implemented a different solution to the T/R switch and plan to add the series resistor to protect the voltage-doubling circuit diodes. The IRF510 circuit seems to be more stable, so unless I see a lot of issues with it here in the group, I do not plan on implementing the mods. As I stated in response to a request from Jens, I am happy with the hardware.? The software still needs work. /g/BITX20/message/10738573 Evan AC9TU
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I believe this thread?describes all the differences.? If you are happy with the V2 hardware, there is no need to upgrade to the V3 hardware. In summation, the V3 finals are more robust, at the cost of less power output.?? If you're using your V2 hardware and aren't roasting your finals, you're fine. Personally if we do see a kit with all the parts to do an upgrade, I'll buy one, just in case. Note when people are talking about 'V3 upgrade' they may also be talking about upgrading to the new software. You can use the V3 software on the V2 hardware, the changes work fine on both. -- Regards, Dave, N1AI
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Thanks for all the replies on this thread Evan, Gordon, and Dave!!? For me, I’ve dialed back the gain and am perfectly happy with 5-10 watts maximum power output.? If I need to run more than that I just use my IC7300.? Not need to push my V2 to the limits.? I’ll stick with my current hardware a move on with the V3 software updates. ? Steve W5RRX ?
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From: [email protected] < [email protected]> On Behalf Of Dave, N1AI Sent: Tuesday, January 2, 2024 3:19 PM To: [email protected]Subject: Re: [BITX20] V3 versus V2 SBITX Board - What are the differences? ? I believe this thread?describes all the differences.?
If you are happy with the V2 hardware, there is no need to upgrade to the V3 hardware.
In summation, the V3 finals are more robust, at the cost of less power output.??
If you're using your V2 hardware and aren't roasting your finals, you're fine.
Personally if we do see a kit with all the parts to do an upgrade, I'll buy one, just in case.
Note when people are talking about 'V3 upgrade' they may also be talking about upgrading to the new software.
You can use the V3 software on the V2 hardware, the changes work fine on both.
--
Regards,
Dave, N1AI
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I am stuck with a 90 day old non-functional v2 unit, that will not calibrate the new power transistors that I bought.? Yes, I followed all the suggestions give to me in this forum however-- the moment i turn the bias adjustment off counter-clockwise it blows the transistors.
At that point (three sets of transistors replaced)? I was hoping for a response from Farhan about the v3 upgrade components, in hopes that those would give me a functioning radio, but this far I have gotten zero feedback on how to move forward from Farhan, so the sbitx has been shelved. I may just sell it.
Bruce, KF4KKZ
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Bruce,
Remove the finals and verify that the gate voltage is adjustable with the PA_BIAS control.? There could be an open circuit or other fault with the bias adjustment.? You can also validate that the PTT 12-volt circuit functions without the RF feedback potential.
73
Evan
AC9TU
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Had similar issue, brought the bias up too quickly and popped the finals.? Finally brought the bias up very slowly and as soon as it started pulling current stopped all appears to be well. ? Tom KT4XN ? Sent from for Windows ?
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From: blunde04Sent: Friday, January 19, 2024 8:31 PM To: [email protected]Subject: Re: [BITX20] V3 versus V2 SBITX Board - What are the differences? ? I am stuck with a 90 day old non-functional v2 unit, that will not calibrate the new power transistors that I bought.? Yes, I followed all the suggestions give to me in this forum however-- the moment i turn the bias adjustment off counter-clockwise it blows the transistors.
At that point (three sets of transistors replaced)? I was hoping for a response from Farhan about the v3 upgrade components, in hopes that those would give me a functioning radio, but this far I have gotten zero feedback on how to move forward from Farhan, so the sbitx has been shelved. I may just sell it.
Bruce, KF4KKZ
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When adjusting the power stage after replacing the FETs, it is important that your power supply has a current limit.
Otherwise, you can replace the FETs again after the replacement.
So set the power supply to 12V and the current limit to a maximum of 2.00A.
In this case, you do not have to replace the previously failed parts again, even if the setting is incorrect.
Oh, and the antenna connector should have a dummy load, because the radio frequency is displayed there.
--
Gyula HA3HZ
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I had this with my v2, I replaced the bias pot with a 10 turn 10k and it was a much smoother adjustment. Don't know why they don't fit them anyway with the setting being so critical? G0RCL.
On Sat, 20 Jan 2024 at 07:10, HA3HZ < gyula@...> wrote: When adjusting the power stage after replacing the FETs, it is important that your power supply has a current limit.
Otherwise, you can replace the FETs again after the replacement.
So set the power supply to 12V and the current limit to a maximum of 2.00A.
In this case, you do not have to replace the previously failed parts again, even if the setting is incorrect.
Oh, and the antenna connector should have a dummy load, because the radio frequency is displayed there.
--
Gyula HA3HZ
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Thank-you for that feedback, I will have to see if I can borrow one that has the capability, my astron does not.? I fear replacing again will cause problems with the pads lifting, so I will wait until I can get the retrofit parts with the better v3 transistors and accompanying resistors I saw in the posts. Dummy load was used in prior efforts, so will continue to use that in the next repair attempt.
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Evan, thank-you. I will check this as well.
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Owen,
Thank-you -I will look into a ten turn 10k to replace with.
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Re-reading over the "sbitxv3 PA changes and measurements" doc* I see this item, but I don't recall reading of anyone making the changes (nor the other 2 changes preceding this).
3. The standing current in the diodes that switch the LPFs was found insufficient on 3.5 MHz, hence, the resistors R201, R202, R203 and R204 are changed from 470 ohms to 330 ohms.
Just how "insufficient" was the current, and is it recommended? I have V2 hardware.
Thanks,
Mike
*
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Hi Mike,
The problem of the diode LPF switch current comes up when measuring the spurious content for 80 meters.? The variations of Diodes and other filter components will come into play.? I would guess that most will not have the issue.? I do not have a V2 to test the assumption.? As far as I know, the change does not impact any of the other parameters.? If I had a V2 board, I would make the change.
This also points out that since the sBitx is sold as a kit, it is up to the Ham to verify conformance to local signal purity standards.? The purchaser should test the kit to ensure conformance.
73
Evan
AC9TU
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Dave, N1AI
HA3HZ