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Dear Paul,
Thank you for that clarification.?? 1N4148 across the choke? with the cathode towards the 12V lead.?? OK? I got it.
Take care and have fun.? Happy Labor Day weekend
73 Dave WA5DJJ
SUPER QRSS/WSPR GRABBER
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Here’s how I’ve protected the BS170’s with Zener diodes with no side effects as far as I could tell. It’s been reported here before, but I hope it’s OK repeating? -- Sverre
LA3ZA
http://la3za.blogspot.com
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Transient Voltage Suppression (TVS) devices are more appropriate protectors than Zeners. They are designed to absorb overvoltage transients and react faster than Zeners which are designed to operate as voltage regulators. Zeners also have much larger shunt capacitance.
Transient Voltage Suppressors (TVS) and Zener diodes are both used to absorb excess energy and protect your circuit from damage when voltage levels spike above the device’s clamping voltage. What’s the difference between them?
Comparing the two, TVS diodes have a faster response time (ns level) and a higher surge current absorbing ability, making them more suited to instant circuit protection against transient voltage spikes. When a TVS diode suffers from high transient voltage, the diode’s resistance changes from high to low very quickly, absorbing the transient current and protecting your delicate downstream devices. Then the voltage is clamped down to a fixed value to prevent high peak voltage from damaging your protected chips.
Gary
W9TD
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Gary,
I totally agree with your comments using a TVS. That’s the right way to do it. Zener is a poorman’s junk box solution. Zeners can be found in junkbox, at least in my case and TVS are more specialty diodes :)
I use zener diodes in all my design radios and now on my QDX and QMX, no PA BBQ problems so far after my initial QDX PA hiccups.
73
Barb WB2CBA
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Dear Sverre,
Thank you for your explanation and you website that did a really good job of telling me what I wanted to know.? I will go find me some 47V Zenner diodes.?
Take care and have fun. I hope to work you on my QDX's when I get them finished and tested.
73 Dave WA5DJJ
SUPER QRSS/WSPR GRABBER
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Thank you Sverre,?? I went to the link you provided and saw and read what I think I need to do.? Hope I can work you when I get my QDX's finished and tested.???
Take care and have fun.
73 Dave WA5DJJ
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On Thu, Aug 31, 2023 at 08:23 AM, Ted 2E0THH wrote:
The finals don't need any protection.
You are incorrect. Even a perfect antenna is subject to random events such as antennas falling down or coax faults.? A couple of diodes are cheap insurance for unforseen high-VSWR situations. --- Zach N0ZGO
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Well call it the pilot in me.
I have an old check list I perform prior to any transmission and have never blown any final in all my years.
On my vintage valve transmitters, cooking output tubes would be a somewhat more expensive exercise.
Ted
2E0THH
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Dave,
When you do the diodes across all your rigs lets us know if any issues you come up against. ?I have a built QMX, a QDX kit and another QMX kit in the boxes and want to be as protective as I can be.
Thank you.
Dave K8WPE since 1960 David J. Wilcox’s iPad
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On Sep 2, 2023, at 11:26 PM, David R. Hassall WA5DJJ <dhassall@...> wrote:
?Dear Paul,
Thank you for that clarification.?? 1N4148 across the choke? with the cathode towards the 12V lead.?? OK? I got it.
Take care and have fun.? Happy Labor Day weekend
73 Dave WA5DJJ
SUPER QRSS/WSPR GRABBER
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Hi Zach, Ted, all
Making a transmitter completely resilient to any SWR mismatch is quite a hard task. It considerably increases the complexity (and thereby costs). I think this is what Ted was referring to, when he said "Wild SWRs will do for every transmitter I own, this was drummed into me early on." - in other words, none of his transmitters could withstand every possible SWR mismatch. And that the best possible protection is to go through a series of mental checklists before transmitting. Which is what I do every time too. Before I switch on the power supply, I'm always mentally tracing the cables on my workbench from the unit I'm going to switch on, to which power supply, anything else connected to that power supply, what voltages any of these things are accepting, what voltage the power supply is currently set at, what rig is the antenna connected to, did I unplug it for a storm, blah blah.?
I'd also like to remind everyone that a couple of weeks' back I posted here, wish I had the post reference handy, where I did a quick experiment?- QDX with open load, and short-circuit load. In neither case was the voltage at the drains anywhere near the 60V limit of the BS170s. Which doesn't mean that there IS no type of mismatch which would cause a high voltage at the drain; but I would challenge anyone to identify such a load and experimentally verify that it does create a > 60V drain voltage on the QDX finals.?
If such a traumatic load is non-existent or very unlikely, then by adding the 47V Zener you are achieving nothing? or almost nothing against high voltages due to SWR mismatch.?
The other ways bad SWR could cause problems are high current, or high power dissipation causing overheating. I think this is much more likely (the short-circuit load causes high current consumption) but it is not addressed by the 47V zener.?
What the 47V zener DOES do, and also the diode across the PA choke, is to eliminate a very short (sub-microsecond) spike at key-down which occurs due to the sudden dI/dt in the choke (the RF envelope isn't shaped). One may speculate that this spike causes avalanche breakdown in the BS170s which is a bad thing and one may speculate that it can contribute to stress that makes the BS170s more likely to fail; however these are speculations without experimental evidence.?
So in the end I think protecting against high current versions of SWR that cause failure due to overheating is the more important thing - but it is not being addressed by the zener or 1N4148 diode solutions.?
On Mon, Sep 4, 2023 at 10:20?AM Ted 2E0THH < qrp@...> wrote: Well call it the pilot in me.
I have an old check list I perform prior to any transmission and have never blown any final in all my years.
On my vintage valve transmitters, cooking output tubes would be a somewhat more expensive exercise.
Ted
2E0THH
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Hello Dave
I don't yet see any evidence that there is a high voltage scenario?that the zener diodes protect against.?
The diode across the choke protects against a short 1us spike. Which one can speculate may be damaging but again there isn't evidence for this either. Bear in mind also that this only applies to QDX. QMX has RF envelope shaping so there is no dI/dt issue, no spike.?
On Mon, Sep 4, 2023 at 12:09?PM David Wilcox K8WPE via <Djwilcox01= [email protected]> wrote: Dave,
When you do the diodes across all your rigs lets us know if any issues you come up against.? I have a built QMX, a QDX kit and another QMX kit in the boxes and want to be as protective as I can be.
Thank you.
Dave K8WPE since 1960 David J. Wilcox’s iPad On Sep 2, 2023, at 11:26 PM, David R. Hassall WA5DJJ <dhassall@...> wrote:
?Dear Paul,
Thank you for that clarification.?? 1N4148 across the choke? with the cathode towards the 12V lead.?? OK? I got it.
Take care and have fun.? Happy Labor Day weekend
73 Dave WA5DJJ
SUPER QRSS/WSPR GRABBER
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Gary, can you suggest an appropriate TSV we could use?
Thanks,
Dean - KC9REN
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On Sun, Sep 3, 2023 at 08:35 AM, Gary W9TD wrote:
Transient Voltage Suppression (TVS) devices are more appropriate protectors than Zeners. They are designed to absorb overvoltage transients and react faster than Zeners which are designed to operate as voltage regulators. Zeners also have much larger shunt capacitance.
Gary
W9TD
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Hello Ted,
When the point is not to leave something undone component survival is less?than that of life itself.? While I might make a checklist nearly the same as yours.? Still, I'd love to have a tried and true checklist that works.? (I am a new HAM with few months of experience and a new QDX, assembled at home that has not had exposure with a 12 Volt-supply.? If I followed them, the assembly steps is such a checklist as well and the transceiver will work).? Could you share your checklist, please??? ? Paul KY4XJ?
------- Original Message -------
On Monday, September 4th, 2023 at 3:20 AM, Ted 2E0THH <qrp@...> wrote:
Well call it the pilot in me.
I have an old check list I perform prior to any transmission and have never blown any final in all my years.
On my vintage valve transmitters, cooking output tubes would be a somewhat more expensive exercise.
Ted
2E0THH
_._,_._,
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Dear Hans,
I appreciate and trust? your analysis and my version 1 QDX worked really great once I solved all of the SWR and power adjustments to using a 12VDC power supply adjustments.? I understand that the testing you have done pretty well proves to me that it is some kind of external event that is blowing the BS170 FET's on some of the QDX's and it doesn't seem to be limited to one version of QDX.? Since I plan to loan out or give my version 3 QDX's and they may end up in places where the folks may not be astute to making sure the power supply is exact or the antenna SWR is less than 2:1.? I want to make them as bullet proof as I can to prevent failure.? I understand that your testing and some of mine proves pretty well that the failure of the PA section of the QDX shouldn't happen unless it is abused.? Maybe the addition of these inexpensive parts will improve the reliability for the failures that are caused by things that we can't reproduce the modes that caused the outlying failures.
So, I am going to put two 3 amp power diodes in the power line to drop the 12V to 10.5VDC.?? Since I ordered the 47V Zener diodes, I am going to add them to the QDX output amplifier and I am going to put the 1N4148 diode on L14.? I am only doing this to prevent the QDX from self destruction during the time that the new operator has time to learn to check the other killer things that causes failures.?? I want them to experience the same amazement of 40M contacts to the far east with a ground mounted vertical antenna with 3.5 watts when the station calls them.? Or working all over the USA on JS8CAL using this amazing little black box with no knobs.?
Thank you for your message.? I will be keeping track of these 5 QDX units and try to record the failures we have to build a data base.? Thanks to all who have also put their thoughts and possible solutions for the failure of the QDX's BS170 Final Amplifiers. All of the efforts have given us all some really good background on their results and cures for the rest of us to try.?
Take care and have fun.
73 Dave WA5DJJ
SUPER QRSS/WSPR GRABBER
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I agree with Hans.? However, its more than cost or size.
From experience...
Adding protections considerably complicates the transmit section and adds
a large number of parts that can also fail or if kitted be damaged in assembly.
It also can if "broken" cause a larger number of problems that for the inexperienced
would be annoyingly difficult to repair.
Add to that the best protection is prevention and that means making sure the load is?
a reasonable approximation as high SWR can mean unusually low impedance,
or unreasonable reactance that presents a troublesome load.
From my experience in antennas the number of cases where it "works great"
usually meant an untuned antenna, out of band antenna or if more than one?
the wrong antenna. When corrected the usual response was "Wow" or "why?
did it work before?".? What is forgotten is anything can radiate, doing it well
can make a massive difference.? ?
--
Allison
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Post online only, please no email.
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Hello Paul
I will be delighted to send my checklist over. I am working down in London this week but will forward it on at the weekend.
A few years back I purchased a NanoVNA which I switch onto my antenna as part of the SWR check. It will instantly show if there is anything untoward going on.
I think I paid ?32 for it and now a vital part of the shack for many other applications too.
73s Ted
2E0THH
?
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I have not tried them, but I like the following devices, stocked at digi-key
? (leaded)
?or?? (45V versions)
Gary
W9TD
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Hello,
I see many post that will put diode or zener.
But what do you think about putting a capacitor at the midpoint of T1?
(or the opposite pin of L14, the one not plugged into C37). Maybe a
2x1uF ceramic.
73
Nicolas F4EGX
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Le mar. 5 sept. 2023 à 00:25, Gary W9TD <w9td@...> a écrit :
I have not tried them, but I like the following devices, stocked at digi-key
SMF43A (SMD)
1SMA43AT3G (leaded)
1SMB45AT3G or 1SMA45AT3G (45V versions)
Gary
W9TD
--
-------------------------------------
Nicolas CHATELAIN
F4EGX.67@...
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These TVS Zeners have huge capacitance. Wouldn't that be an issue in the finals circuit?
--
73, Dan? NM3A
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Dan,
The Zener diodes suggested have about 150% the capacitance of the TVS. The capacitance is measured at zero volts, at 9 or 12V, the capacitance is about 1/4 the value at zero volts. Each BS170 has about 20pF of capacitance at operating voltage and two are in parallel. So the TVS would add about the same capacitance that is already there, so a little less than 100pF total. Maybe not optimum but reports with Zeners don't show much difference in operation without them.
Gary
W9TD
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Gary W9TD
Barb WB2CBA
Ted 2E0THH
David Wilcox K8WPE