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Re: SSB Calibration blown finals
Tony's,
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The fix Hans put into the SSB firmware to avoid blown finals?
is to periodically give it a rest so the finals can cool down.
If that does help (and my impression from forum reports is that it probably does),
then current can also be a problem.
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Fortunately, the TN0110's can deal with both more voltage and more current than the BS170's.
So if they can transmit clean SSB on the QMX, that's a big win either way.
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Jerry, KE7ER
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On Mon, Mar 24, 2025 at 07:15 PM, Tony Scaminaci wrote:
Over the past year or so, it seems we came to an unofficial conclusion that BS170s were blowing due to high drain voltage as a result of high SWR or exceeding 12VDC at the supply input rather than overheating due to high current. TN0110 has a significantly higher drain voltage advantage over BS170 (100V vs 60V) and if it works well with SSB, I’ll be very happy. Keep us posted on your SSB adventure with TN0110. |
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Evan,
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Had always assumed that topology of those filters would present a high impedance to all harmonics.
I've attached an LTSpice simulation for the output LPF's on 80m
as used on the QCX, QCX_50W_Amp, the QMX, and the uBitx.
Does an AC Analysis on all of them from 1mhz to 20mhz.
Will archive those two (very small) files under KE7ER in the files section.
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You can click on the output node to see the voltage across the 50 ohm resistor,?
or click on the voltage source to see the current going into the LPF, which is inversely proportional to impedance.
Things look considerably more complicated than I was expecting.
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Looks like somewhere around the second harmonic, it's fairly high impedance looking into the LPF.
For the higher harmonics, that impedance is generally no more than the it is for the fundamental.
A push-pull amp should mostly take care of the second harmonic, and giving the odd harmonics an easy path to ground
suggests to me that these are most suited for a current mode amp.
So perhaps the QMX would do better with two L502's, so the two phases of BS170's can have their drains uncoupled.
This is what the uBitx final does.
The QCX 50W amp uses two windings on T2 to supply power to the FET's, that's equivalent to feeding power at
the center tap of the output transformer primary, and best suited for a voltage mode amp.
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I have only recently found that these amps can be classified as voltage mode or current mode,
and so may be a bit to fixated on it.? ?It seems the distinction is not always as clear cut as I had expected.
All of these amps seem to work well enough, though I still wonder if the QMX could be more robust.
Could be that the best path is to just replace the BS170's with TN0110's when they blow..
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Jerry, KE7ER
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On Mon, Mar 24, 2025 at 02:36 PM, Evan Hand wrote:
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Re: SSB Calibration blown finals
开云体育
Thanks. The jury is still out for me since I have not managed to get good results with SSB yet. The microphone I tried worked but the audio was noisy and sounded distorted. I decided to order the electret that Hans is using to put one more stake in the ground
before experimenting further. I think it may just be a matter of getting all the settings right. If I start with his mic, I stand a better chance at getting there.
Tony
AD0VC
From: [email protected] <[email protected]> on behalf of Tony Scaminaci via groups.io <tonyscam@...>
Sent: Monday, March 24, 2025 8:15 PM To: [email protected] <[email protected]> Subject: Re: [QRPLabs] SSB Calibration blown finals ?
Hi Tony,
It’s good to hear that the calibration using TN0110 was similar to that of the BS170. I was initially concerned about SSB performance but when Hans mentioned his calibration technique, I had one of those Ah-Ha moments with hopes for a good outcome.
Thanks for running the calibration on both devices.
Over the past year or so, it seems we came to an unofficial conclusion that BS170s were blowing due to high drain voltage as a result of high SWR or exceeding 12VDC at the supply input rather than overheating due to high current. TN0110 has
a significantly higher drain voltage advantage over BS170 (100V vs 60V) and if it works well with SSB, I’ll be very happy. Keep us posted on your SSB adventure with TN0110.
Tony - AC9QY
On Sun, Mar 23, 2025 at 11:15?PM mux_folder2001 via
<canthony15=[email protected]> wrote:
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Re: SSB Calibration blown finals
Hi Tony, It’s good to hear that the calibration using TN0110 was similar to that of the BS170. I was initially concerned about SSB performance but when Hans mentioned his calibration technique, I had one of those Ah-Ha moments with hopes for a good outcome. Thanks for running the calibration on both devices. Over the past year or so, it seems we came to an unofficial conclusion that BS170s were blowing due to high drain voltage as a result of high SWR or exceeding 12VDC at the supply input rather than overheating due to high current. TN0110 has a significantly higher drain voltage advantage over BS170 (100V vs 60V) and if it works well with SSB, I’ll be very happy. Keep us posted on your SSB adventure with TN0110. Tony - AC9QY On Sun, Mar 23, 2025 at 11:15?PM mux_folder2001 via <canthony15=[email protected]> wrote:
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Re: QDX
First off, I would like to thank all those that offered help.? Especially Hans.? He recommended I replace the finals.? I did so tonight.? Start up went without any issues, then the LED dimmed and went out.? I was able to restart it, but same thing happened.? Now it will not stay on.?
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I am in no way bashing the QDX, or QRP Labs.? I believe it is builder error.? I do not know what the issue could be.? I see the trash can for this little device unless I can find someone local to help me.? I would buy a prebuild unit over a kit if the opportunity presents itself in the future.
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Thanks
73 KQ4SID
Craig |
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Re: QMX Won’t turn on
Appy 3.3V to the mic input?? Why?????
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The KEY? lines (dit/dah) they would not like DC applied to them
as they are input direct to the micro.? ? For SSB I think one is
hooked to the A/D which is ac coupled but a sharp transient
of 3.3V might just hit the input too hard.
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ITs 2.2K to 2.2V rail so that not? it but the A/D input are nominally
biased to half the Vdd (3.3V).? The mic input is though a .1uf cap.
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Likely killed the micro.
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Allison ------------------ Post online only,? direct email will go to a bit bucket. |
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Here’s an idea…
Is Hans going to Dayton Hamvention this year?
How about a troubleshooting class for the QMX and QMX+ product line? Some discussion to common problems and resolutions to the problems. It would be great to hear from other technical specialists on this product as well. Perhaps some discussion on upcoming products and or FW revs.
Of course bring plenty of kits and parts to sell to repair the kits that have failed for whatever reason.
I would entertain coming to Hamvention for that alone.
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Don. |
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Re: QMX Won’t turn on
First, a reminder to all:? Please DON'T CONNECT ANY EXTERNAL VOLTAGE TO THE QMX/QMX+ MIC/PADDLE INPUT.
For electret mics, QMX/QMX+ already has an internal 3.3V bias voltage hooked up to the mic input (ring terminal) of the connector.
And indeed, only electret mics, or other high-impedance mics should be used.? There is also an internal DC-blocking capacitor on the microphone signal.? The 'tip' and 'ring' terminals of this connector also hook directly to processor input pins (for the paddle dit/dah) in addition to the processor microphone input - so external voltages improperly applied may cause damage.
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Now, on to your problem (QMX won't turn on, per the message title):
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Looking at the schematic, I don't see how connecting 3.3V to any of the terminals of the mic input jack could cause damage such that the QMX would fail to turn on.? Unless there was some other factor, like perhaps an ESD event.? Or if the voltage applied for some reason was 6V or 9V or 12V, it indeed could have caused damage to either the processor or to the 3.3V power supply - this could happen, for example, if you were using a external supply for the 3.3V bias, and turned it from off to on while connected - some supplies can spike significantly above their set voltages when turned on, or spike well below ground potential when turned off.
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Since your QMX won't turn on, somehow either the power supply or processor was damaged - hopefully only the power supply, since it is much easier to fix/replace.? The protection diode in the 3.3V supply could have failed if there was over-voltage.? Or over-voltage could have fried some input pins on the processor, preventing it from starting up.
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A good measurement to make is the current draw while you have the PWR_ON button pressed (but don't press it too long unless you have a current-limited power supply set to about 250mA).? This can help tell what kind of fault is present.
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Then I would remove the bottom cover, and (with no power attached), and measure the resistance between GND and the three voltage busses (12V, Vcc, and Vdd).? You can find the contacts for those busses on the soldered SMPS connector pins.? (Someone just today or yesterday posted a message with a nice pdf identifying all of the voltage pins on the bottom of the QMX card).? I? suspect the resistance between Vdd and Gnd will be a low number of ohms (rather than a few K-ohms).? Such a low reading would indicate a failed component or short.? Next step would be to disassemble the top cover to get to the SMPS cards and remove them.? Then re-measure the Vdd/Gnd resistance on the main board - if it is still low, the processor is likely damaged.? If it is now high (hopefully), then the failure is on the SMPS card, likely D109.? You can use the nice procedure written in the wiki of this list to independently test the SMPS cards, or just order new ones from Hans and replace them.
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Good luck in quickly finding this, and ask if you have any addition questions.
Stan KC7XE |
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Leaving 50-watt amplifier in-line but off
I've purchased the 50-watt amplifier kit, to be built for 80m, and bought assembled the 40m and 20m amps from Ray, VA7SK (very nice solder job, btw); on 40m it certainly makes a noticeable difference of 6dB -10dB on reports and it's much easier to reach Europe.
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Question: Can I leave the amplifier inline between the QDX and the antenna if the amplifier is off?? I'm not seeing that addressed in the assembly manual nor could I find an answer by searching the messages here.? I think so based on the schematic, but I don't trust my circuit reading skills enough to risk the QDX or the amplifier.??
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Thanks,
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Jim
K8DDV |
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With those settings turned on, you will be getting about 20dB lower of a signal from your mic to the audio path (compared to when the setting is turned off) - so it may be reacting with other downstream settings that require a minimum amplitude.
Crank up that 'global gain' parameter so the output of the EQ when 'on' will be similar to when 'off', and the choppiness should go away. |
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Re: QMX+ Strange Audio Artifact - Help, Please...
Hi Jim,
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L501 or C504 failure can cause these symptoms. ?Make sure to have about 2 ohms continuity on l501 at the pcb pads. ?It’s a little difficult to test C504 in circuit. ?These big tantalum’s fail though. ?You can remove it and test it on the bench.
It’s hard to diagnose the exact problems in the bias circuitry. ?There is interaction everywhere. ?But if you look around with a scope, you can often get a clue to what’s failing. ?Most often it’s one of the transistors, the coil being broken or the big cap failing.
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if you can’t find the culprit in that bias circuit, certainly send it along to me. ?
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73 Jeff Moore W1NC |
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