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I?m very angry about the tx quality of the high bands QDX, Rev 5. my first QDX high bands (rev3) was killed after a few day working good. I decided to buy a new one assembled. After 4 Months waiting I received it today. Testing the 20m Band with 12 Volts exactly and a Z-Tuner and lw with swr better than 1.5 I could start and got a QSO with a station in Russia. I used no Case. Trying to start a cq call I got an answer from a station in GB. While sendig and returning the call one of the BS170 went into smoke. I?m shure that I didn?t make any mistake. Sorry Hans , the trx system push to pull without any Protection is a peace of shi.... I can?t put it in other words. I?m very frustrated and agry. Using? the same frequency, voltage and antenna, i could make QSOs without any problems with two other competition KIT trx ,? the ADX-s and the QRP-Guys Digital III trx . These devices uses 3x BS170in parallel like the QCX. But are protected wit a zener diode. These devices, also for the high sw bands (20-10m Modules) never failed. I could make a few hundred qsos on all bands between 20m and 10m. What is the advantage of a hightech QRP transceiver, with better signals and better receiving results (thats true , absolutely fantastic QDX ), when the trx will not survive a handful of qsos ? especially the high bands QDX seems to have this problem.
I hope that the QMX KIT(ordered in May) will not make this problems. Hans you told me in Friedrichshafen , that it is protected against high voltage and bad SWR.
73 de Matt
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Matt,
That's why I dumped QDX, however, had I known about the simple zener-fix, then I might have stayed.. GL with QMX - someone at least saw fit to add Zeners!
73
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Experience is very contrary to that of most QDX users.? Maybe when you calm down a bit you can send a somewhat more objective email and we can help you. ? Mike WM4B ?
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From: [email protected] < [email protected]> On Behalf Of mweidle@... via groups.io Sent: Saturday, July 15, 2023 2:48 PM To: [email protected]Subject: [QRPLabs] New assembled High Bands QDX went into smoke ? I?m very angry about the tx quality of the high bands QDX, Rev 5. my first QDX high bands (rev3) was killed after a few day working good. I decided to buy a new one assembled. After 4 Months waiting I received it today. Testing the 20m Band with 12 Volts exactly and a Z-Tuner and lw with swr better than 1.5 I could start and got a QSO with a station in Russia. I used no Case. Trying to start a cq call I got an answer from a station in GB. While sendig and returning the call one of the BS170 went into smoke. I?m shure that I didn?t make any mistake. Sorry Hans , the trx system push to pull without any Protection is a peace of shi.... I can?t put it in other words. I?m very frustrated and agry. Using? the same frequency, voltage and antenna, i could make QSOs without any problems with two other competition KIT trx ,? the ADX-s and the QRP-Guys Digital III trx . These devices uses 3x BS170in parallel like the QCX. But are protected wit a zener diode. These devices, also for the high sw bands (20-10m Modules) never failed. I could make a few hundred qsos on all bands between 20m and 10m. What is the advantage of a hightech QRP transceiver, with better signals and better receiving results (thats true , absolutely fantastic QDX ), when the trx will not survive a handful of qsos ? especially the high bands QDX seems to have this problem.
I hope that the QMX KIT(ordered in May) will not make this problems. Hans you told me in Friedrichshafen , that it is protected against high voltage and bad SWR.
73 de Matt
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Matt,
A ham friend of mine operated his QDX without any antenna connected by mistake.
I repaired my friend’s QDX which had damaged BS170s and IC5 74ACT08. After replacing those QDX worked flawlessly.?
As a precaution I added two 1N4756 47 V/1W zener diodes as shown in QMX manual. He is very happy with it. After this repair session he confessed that he operated QDX without antenna connected once more by mistake and BS170s and QDX are still alive he said!:)
May be you should try this too.
This is the screenshot I used from QMX manual:
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Hi Barb,
thanks I will try to replace the 4 BS170 and the 74ACT . In addition I will order two zener Diodes. But it is not easy to get these Zener diodes . High costs of shipping.
?We know us from the crkits io :) .The QDX is such a good trx but Im angry a little bit . especially because I don?t see the reason of a fault. VOltage <= 12 V, swr better 1.5
73 de Matt
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Thanks, I like Hans and his products but It is so frustrating, when you know the fault seems to be not in your own responsibility. I also got comments that zener diodes have no results of... yes german hams...
72 de Matt
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I of course don’t know from start to finish how firm all of the statements are but after having been in electronic for the best part of my working career, my guess failure was most likely due to a faulty component. ?In analytical control manufacturing we would burn in the equipment for 30 hours or so before making financial adjustments prior to sending the equipment to its destination.
Back then heat was generated that had to be compensated for the expected operating conditions. ?Some components at the time would change characteristics as a conditions changed…… some FAILED, and that’s why we would burn the equipment in.
I still have some stuff running from the 70’s so I have to think it was built OK.
When I get a new “whatever” today I assume that very little real testing & burn in has been done so I watch the processes especially for the first 30 or so hours, no smoke it’s a go !
I step down,
John ?Each mistake is a learning opportunity.?
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On Jul 15, 2023, at 4:38 PM, mweidle@... via groups.io <mweidle@...> wrote:
?Thanks, I like Hans and his products but It is so frustrating, when you know the fault seems to be not in your own responsibility. I also got comments that zener diodes have no results of... yes german hams...
72 de Matt
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WB2CBA,
The Zener trick you mention has been around and written up by some others before. After I found out about it, I added 51 V 1 W Zeners to my QDX and incorporated them into my QMX. I have 3 QCXs too. I have not added it to them as I am not sure what the extra capacitance will do to the LPF in the class E final. I'd be interested in hearing if anyone has done that in their QCX.
Considering the issues some have had, I consider myself lucky to have not had any finals failures with my 5 QRP Labs transceivers. I attribute much of it to fastidious attention to antenna system matching, but some of it must be just plain luck.?
--
73, Dan? NM3A
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The relevant voltage is NOT 12V.? The RF voltage is over 40V.? For 5W into 50 ohms the voltage is roughly 47 V p-p.? If the SWR is greater than 1:1 the voltage goes up.? The BS170 has a max voltage of 60V, so it's running near breakdown
dave k2lyv
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That goes mean, better using only 11V to get not more than 3-4 Watts to protect the BS170 transistors. In this case two zener diodes make really sense. better to have trx with 3-4 Watts working than a damaged with 5 Watts output.
72
Matt, DL1SER
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I could fix the fault. Got 4 new BS170 and changed the 74ACT now only using 10V supply .I got 3 Watts Output. Until I get my zener Diodes I will not use a higher Power
73 de Matt
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Matt,
AliExpress has the Zeners, 1N4756, 1W 47v. I'm not in the US/EU, but they are very cheap here, about a dollar for 50 and a dollar for shipping.
73,
Casey, NA7U
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Dave and I have discussed this at length; there are a large quantity of chewed-up textiles from our discussions. To add to his comments,? his calculation below is based on 50 + 0i? ohms, which is a PURELY RESISTIVE load with a SWR of 1:1. Even if Z = 50 ohms, you can have V >> 47 V p-p if the load is reactive. If you want to play with the math, try calculating the impedance a 30 ohm resistive with first a 40 ohm inductive reactance then a 40 ohm capacitive reactance........................
Lee KX4TT
On Sunday, July 16, 2023 at 04:02:24 AM EDT, David Birnbaum <dbirnbau@...> wrote:
The relevant voltage is NOT 12V.? The RF voltage is over 40V.? For 5W into 50 ohms the voltage is roughly 47 V p-p.? If the SWR is greater than 1:1 the voltage goes up.? The BS170 has a max voltage of 60V, so it's running near breakdown
dave k2lyv
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The difference between 3 and 5 watts is rather miniscule (for instance, you are copied at -14 or -15 dB instead of -13 dB); why not simply run the QDX at 10 volts?? K2LYV's calculation would then be ~38V (no actual calculation done; I just eyeballed it), which provides a bit more headroom. Of course, all bets are off if the antenna has a highly reactive element (see my last comment). Allison, KB1GMX and others have pointed this out as a reasonable solution; a little bit of applied math (or maths as the folks across the pond would say) bears her and the others out. The zeners may be a perfectly good backup dependant upon the internal capacitance across the diodes, but lowering the voltage a bit is easier.?
Lee KX4TT
On Sunday, July 16, 2023 at 12:10:27 PM EDT, mweidle@... via groups.io <mweidle@...> wrote:
I could fix the fault. Got 4 new BS170 and changed the 74ACT now only using 10V supply .I got 3 Watts Output. Until I get my zener Diodes I will not use a higher Power
73 de Matt
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Just a point of clarification, the BS170 is not driving 50 ohms. There is a transformer in between that reduces the impedance by the square of the turns ratio. And the turns ratio is the ratio of the 50 ohm side of the transformer to the half winding seen by
the BS170. The BS170s will see roughly???of 50 ohms.
Tony
AD0VC
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Dave and I have discussed this at length; there are a large quantity of chewed-up textiles from our discussions. To add to his comments,? his calculation below is based on 50 + 0i? ohms, which is a PURELY RESISTIVE load with
a SWR of 1:1. Even if Z = 50 ohms, you can have V >> 47 V p-p if the load is reactive. If you want to play with the math, try calculating the impedance a 30 ohm resistive with first a 40 ohm inductive reactance then a 40 ohm capacitive reactance........................
Lee KX4TT
On Sunday, July 16, 2023 at 04:02:24 AM EDT, David Birnbaum <dbirnbau@...> wrote:
The relevant voltage is NOT 12V.? The RF voltage is over 40V.? For 5W into 50 ohms the voltage is roughly 47 V p-p.? If the SWR is greater than 1:1 the voltage goes up.? The BS170 has a max voltage of 60V, so it's running near breakdown
dave
k2lyv
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I'm relaxed again. Really a good, very good trx.
After replacement I could work DX on 17m?. 10 V and 3 Watts. That's enough at the moment. I hope not to kill it again.? I think, the high Band qdx is more sensitiv? against high voltage and bad swr??
I built up 3 QDX low, 2 for other Hams. They still work.?
I got a routine in fixing blown away P A s I think.???
The zener diodes will be a good idea anyway. Maybe Hans you can add some zener diodes to the kit. I know you told me, that it's hard to get the good ones who really work. ?.
But I think it's no placebo. And a kind of protection.?
73 de Matt.?
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Interesting that the latest QMX Assembly manual says those diodes are not used so apparently the QMX does not have the Zener diodes installed.
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Matt,
A ham friend of mine operated his QDX without any antenna connected by mistake.
I repaired my friend’s QDX which had damaged BS170s and IC5 74ACT08. After replacing those QDX worked flawlessly.?
As a precaution I added two 1N4756 47 V/1W zener diodes as shown in QMX manual. He is very happy with it. After this repair session he confessed that he operated QDX without antenna connected once more by mistake and BS170s and QDX are still alive he said!:)
May be you should try this too.
This is the screenshot I used from QMX manual:<IMG_2481.jpeg>
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Indeed,?
No more zener diodes... But why?
73?
Matt, DL1SER
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There is a thread where Hans chimes in about the Zeners. It is a QDX thread. It’s worth finding. I think he added the pads in case the QMX needed them.?
--
Colin - K6JTH?
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In April this year, John Zbrozek, KJ4A, and I collaborated on modeling the QDX PA.? The models showed a large voltage spike when the transmission was terminated at the end of a message.? This was verified with an oscilloscope to exceed the 60 volts rating of the BS170.
Practical experience has not shown this to be an issue, as there are thousands of QDX in operation and not a very large failure rate that can be verified as caused by this overvoltage.
Per Hans, the Zener pads were added for the QMX in case you want to add the protection.? Several other kits use Zener protection for the finals.? It was unknown what side effects the Zeners would add to the output signal.? To the best of my knowledge, no one has performed that addition and posted the results of a spectral purity check.? There was also concern about the power output and efficiency of the PA if the Zeners were added.
I have not modified any of my QDX as of this date.? I use the QDX as an exciter for a WA2EBY amp and run it at reduced voltage.? I have not experienced any issues with that setup.? I do not run my QDXs portable.
When I do build one of my QMX kits, I will add the Zeners and do the purity test.? I have been waiting to do that for the operations manual and the final firmware updates that fix the current issues of the QMX CW operation.? ?I have been spending my time on other projects.
To date, I have read one post that indicated the Zeners protected a QDX after repair from a subsequent fault caused by an open antenna connection.? The model does show that transmission into an open circuit does show a high voltage on the BS170 drains that the Zener could protect (for a time, depending on the power rating of the Zener).? It does not show that a shorted antenna has the same high voltage issue, so only 1/2 of the possible extremes are covered with the Zener.
The takeaway for me is that monitoring the antenna SWR is important to watch.? That, and running below the design voltage.? Both of these will be more effective than adding the Zeners.
The above are my opinions based on my experiences.? Please do not take them as absolute facts and investigate before you make any choices.? I would appreciate any feedback to help me learn more.
73
Evan
AC9TU
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Mike Besemer - WM4B
Barb WB2CBA
KK4ITX John
Lee
Colin Kaminski