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Finally what is the best solution to protect the BS170? Solder a 1N4448 or 4148 or 914 in parallel to L14? I read also 2 Zener diodes alongside T1? What should I chose?
73 - Pierre - FK8IH
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Hi Pierre,
my QDXs are built for +12V.
I am using these practices:
- added an antiparallel 1N4148 to L14,
- using a good +12V PS with a 1A current limit (and no higher voltage),
- matching the antenna before using QDX's TX.
73 Bojan S53DZ
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Hi Bojan,
I've read a number of comments about an adjustable current limiting PS and I am wondering what you and others are using and would recommend.
73 - Jon Halterman - KJ4CRW
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The best solution is to use a good, resonant, low SWR antenna. I have made almost 500 contacts with my stock QDX (ver 5) and have had no issues. My QDX is powered by a 12v 1 amp switching supply. Jim WB2LHP
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The finals don't need any protection.
As Jim says, just follow the science of what you are transmitting into and make sure all your antenna connections are sound.?
I would certainly recommend some antenna matching unit, I use a home brew Z-match here.
Wild SWRs will do for every transmitter I own, this was drummed into me early on.
73s Ted
2E0THH
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nvm, I see someone else started a thread with that exact question
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With all due respect - Homes have circuit breakers, smoke detectors, and fire extinguishers for a reason......
It's not that we are purposely risky with electrical and/or fire hazards, but we recognize that components and systems can and do fail, despite operating within safe standards.
I would like more information on the diode solution to protect the BS150s, including the correct polarity for insertion of the diode into the circuit.? I already have ancillary low-profile copper heat sinks installed on my four QCX-Minis, all of which are running a 24/7 WSPR Duty cycle, I am hoping the diodes will help further extend the lifecycle of the heavily used components.? ?I have two dozen spare BS150s in bench stock, however, I've already ruined the thin copper PCB traces on both a QSX-Mini and U3S board by replacing BS150 components; I'm hoping to avoid or minimize replacements in the future.??
I do recognize the good advice to be cognizant of SWR and not push source voltage to the extreme, a common self-inflicted failure factor with these micro devices, but if adding a 10-cent diode will extend the MTBF I'm on board to give it a try.
Thanks?
Brian, AA5H / 3W90K?
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For the QDX, install the 1N4148 in parallel with L14 with the banded end of the diode connected to +12V end of L14.
I personally would like to hear from anyone who has fried a BS170 with this diode installed.
Tony
AD0VC
toggle quoted message
Show quoted text
With all due respect - Homes have circuit breakers, smoke detectors, and fire extinguishers for a reason......
It's not that we are purposely risky with electrical and/or fire hazards, but we recognize that components and systems can and do fail, despite operating within safe standards.
I would like more information on the diode solution to protect the BS150s, including the correct polarity for insertion of the diode into the circuit.? I already have ancillary low-profile copper heat sinks installed on my four QCX-Minis, all of which are running
a 24/7 WSPR Duty cycle, I am hoping the diodes will help further extend the lifecycle of the heavily used components.? ?I have two dozen spare BS150s in bench stock, however, I've already ruined the thin copper PCB traces on both a QSX-Mini and U3S board by
replacing BS150 components; I'm hoping to avoid or minimize replacements in the future.??
I do recognize the good advice to be cognizant of SWR and not push source voltage to the extreme, a common self-inflicted failure factor with these micro devices, but if adding a 10-cent diode will extend the MTBF I'm on board to give it a try.
Thanks?
Brian, AA5H / 3W90K?
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After smoking finals in 3 different bad swr occasions ?that’s what I do to protect my qdx finals and it works. Many use in the field with bad swr and even no antenna connected by error.?
73
Barb WB2CBA
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IMHO, this method is valid also but requires two diodes. Why not eliminate the spike at the source??
If you have two QDX, you might try using the L14 diode in one of them and see if it gives you any issues.
Tony
AD0VC
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Show quoted text
After smoking finals in 3 different bad swr occasions ?that’s what I do to protect my qdx finals and it works. Many use in the field with bad swr and even no antenna connected by error.?
73
Barb WB2CBA
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Note that for the QMX (not the QDX) There are unpopulated holes for potential use of these? diodes at D503 and D504. The jury is out on whether these are needed pending additional testing.
-Steve K1RF
------ Original Message ------
Date 9/1/2023 10:23:44 AM
Subject Re: [QRPLabs] QDX - protection of BS17O PA
After smoking finals in 3 different bad swr occasions ?that’s what I do to protect my qdx finals and it works. Many use in the field with bad swr and even no antenna connected by error.?
73
Barb WB2CBA
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After my QDX's finals bit the dust due to the remote ATU doing a re-tune cycle during transmit, I added some simple VSWR protection devices like shown. These devices are just something I had in my junk parts bins.
I can now transmit without an antenna connected and not destroy the finals. Output spectra was not affected and meets current FCC limits for spurious emissions.
A voltage-clamping diode has been on every <= 5W solid-state QRP rig since .. the 70s? Cheap insurance.
--- Zach
N0ZGO
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My apologies, in my last post I said? "BS150" when the correct part is "BS170".
a BIG Thank You to all who responded with diagrams, diode part numbers, etc....!
I have the required diodes in my Bench Stock, so will implement the change this weekend on all four of my WSPR QCX-Minis...
Appreciate the Help!!??
Brian, AA5H
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QCX mini has a class E pa different than QDX which has class D PA with two sets of bs170s. In qcx mini one 1N4756 zener diode will do the job. In qdx we need two of them.
73
Barb WB2CBA
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On a similar note, here's a simple heat sink that should work well for any of these "finals clamped under a washer" resigns:??
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Ted,
Looks good as long as there are no shorts and you still use the "washer and nut" to force the flat sides of the BS170s to make good thermal contact.
73 Kees K5BCQ
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Thanks all for your comments. I decided to solder a 1N4148 diode in parallel to L14.
Additionnally I always tune my EFHW antenna with a transmatch fed by a NanoVNA until it's perfectly tuned.
And to be sure I missed nothing I ordered with my QDX kit a lot of 10 BS170!
73 - Pierre - FK8IH
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Motorola used to use a neon lamp in their VHF base station receivers at the RF input to ground.? Neon lamps usually start to conduct and light up at about 60 volts.? I wonder if that would accomplish the same thing?
-Jerry AC5JM
On Friday, September 1, 2023 at 04:20:22 PM CDT, <wb2cba@...> wrote:
QCX mini has a class E pa different than QDX which has class D PA with two sets of bs170s. In qcx mini one 1N4756 zener diode will do the job. In qdx we need two of them.
73
Barb WB2CBA
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Dear Group,
I am just finishing up 5 QDX's ..... 3 Rev 3's and 2 Rev 5's.??? I have been trying to follow this thread but it is a little confusing as to what modifications really help prevent destruction of the PA transistors and what parts to use
one should use.... There was mention of putting a 1N4148 across the choke but was confusing as to which way to mount it and something about using a power supply at 12V @1 amp.?? There there was two or three messages that put two diodes (zenners or TVS???)and one had them hooked to a different spot than the others.?? Since, I am a careful sort, who follows Hans Summers instructions to the limit.? But I have also had BS170 FETs fail, I would like to give my 5 QDX's at least a fighting chance of survival,? I would really like to see a message from some one that explains what to do and what to use with part numbers to I can keep all my new QDX's running for a long time.? At least as good as my original version 1 which is still going strong after a couple of final transistor failures and an IC5 failure.??
Hope everyone has a great week.?? If anyone needs any 0805 47uH inductors like L11, I will have 200 of them after September 15 and will gladly share.?
Take care and have fun.
Dave WA5DJJ
SUPER QRSS/WSPR GRABBER
?
?
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"There was mention of putting a 1N4148 across the choke but was
confusing as to which way to mount it"
David-- Cathode towards Vcc!
Paul -- AI7JR
On 9/2/23 16:11, David R. Hassall
WA5DJJ wrote:
toggle quoted message
Show quoted text
Dear Group,
I am just finishing up 5 QDX's ..... 3 Rev 3's and 2 Rev 5's.???
I have been trying to follow this thread but it is a little
confusing as to what modifications really help prevent
destruction of the PA transistors and what parts to use
one should use.... There was mention of putting a 1N4148 across
the choke but was confusing as to which way to mount it and
something about using a power supply at 12V @1 amp.?? There
there was two or three messages that put two diodes (zenners or
TVS???)and one had them hooked to a different spot than the
others.?? Since, I am a careful sort, who follows Hans Summers
instructions to the limit.? But I have also had BS170 FETs fail,
I would like to give my 5 QDX's at least a fighting chance of
survival,? I would really like to see a message from some one
that explains what to do and what to use with part numbers to I
can keep all my new QDX's running for a long time.? At least as
good as my original version 1 which is still going strong after
a couple of final transistor failures and an IC5 failure.??
Hope everyone has a great week.?? If anyone needs any 0805 47uH
inductors like L11, I will have 200 of them after September 15
and will gladly share.?
Take care and have fun.
Dave WA5DJJ
SUPER QRSS/WSPR GRABBER
?
?
|
Pierre - FK8IH
Ted 2E0THH
Barb WB2CBA
Paul - AI7JR