Date   

Re: 50 Watt Amplifier for 80M. Minor error in assembly manual.

Dean
 

I have noticed in other kits, the documentation has included how much wire is required to wind a toriod. While building my QCX I referred to a calculator that was a bid help

Dean
On 7/24/2021 4:36 PM, Steve Greffe - VE3SGV wrote:

Just a heads up people. Not a big deal but save yourselves a bit of a headache. On page 13 of the assembly manual we're instructed to cut a 34cm length of .6mm wire to wind L6. For 80M we need 27 turns. 34cm of wire will only get you 22 turns. Not enough for L6 and not enough even for the 24 turns needed for L4 and L7. 
50cm is enough for L6 for 27 turns.
45cm is enough for L4 and L7's 24 turns.
There is still just enough .6mm wire left over to wind the bifilar and trifilar transformers.
I was able to salvage and straighten my initial 34cm piece of wire to use for the bifilar wind. After cutting 50cm and two 45cm pieces, I cut the leftover into 4 equal pieces. They were about 35cm each. 

(I'm building this amp on a picnic table while camping and I have very few other bits and pieces with me other than the kit contents themselves hi hi)

Disaster averted!

Hope this helps others.

73
Steve VE3SGV 

--
Dean Davis, N7XG


50 Watt Amplifier for 80M. Minor error in assembly manual.

Steve Greffe - VE3SGV
 

Just a heads up people. Not a big deal but save yourselves a bit of a headache. On page 13 of the assembly manual we're instructed to cut a 34cm length of .6mm wire to wind L6. For 80M we need 27 turns. 34cm of wire will only get you 22 turns. Not enough for L6 and not enough even for the 24 turns needed for L4 and L7. 
50cm is enough for L6 for 27 turns.
45cm is enough for L4 and L7's 24 turns.
There is still just enough .6mm wire left over to wind the bifilar and trifilar transformers.
I was able to salvage and straighten my initial 34cm piece of wire to use for the bifilar wind. After cutting 50cm and two 45cm pieces, I cut the leftover into 4 equal pieces. They were about 35cm each. 

(I'm building this amp on a picnic table while camping and I have very few other bits and pieces with me other than the kit contents themselves hi hi)

Disaster averted!

Hope this helps others.

73
Steve VE3SGV 


Re: Receiver front-end filter #rcvr

Albert Tatlock's Greatest Hits - Vol 1
 

Good old fashioned moving caps are things of beauty these days.


Re: Receiver front-end filter #rcvr

Jim Allyn - N7JA
 

If you use varactors to tune your filter, be sure that the varactor reverse bias does not approach zero.  If the signals approach the level of the varactor bias voltage, you will have intermod.  Even better, use two varactors back to back.  If you can't get enough capacitance with two of them in series,  then add another varactor pair in parallel.


Re: Fried my qcx+ finals...

M0PWX
 

When I got my U3s I was advised by a local ham to solder turned pin sockets for the BS170 to make changing them easier, as they are easy to blow if you don’t get the biasing right

 

And for higher bands shorten the BS170 leads for stability if using sockets

 

Not sure what others think but there seemed to be a reasonable logic to it

 

73

 

Peter

M0PWX

 

Sent from Mail for Windows 10

 

From: Yannig - F4IUJ via groups.io
Sent: 24 July 2021 20:45

 

Worse is that I didn't notice it immediately, so it might have transmitted for a few 2munites cycle in nothing.

 


Re: Fried my qcx+ finals...

Yannig - F4IUJ
 

Worse is that I didn't notice it immediately, so it might have transmitted for a few 2munites cycle in nothing.


Re: Fried my qcx+ finals...

Bill Cromwell
 

Hi Yannig,

I feel your pain! That word "oops" was not coined just for that one mistake I made one time :)

73,

Bill KU8H

bark less - wag more

On 7/24/21 4:00 PM, Yannig - F4IUJ via groups.io wrote:
On Sat, Jul 24, 2021 at 06:53 PM, VK5EEE wrote:

Lou, if Q6 is blown Open it won't be able to provide DC to Q1,2&3
and will result in no power out. If Q6 is blown Shorted it will
provide DC to Q1,2&3 all the time. This may or may not cause
problems with the finals as they don't go into conduction until
the gates go high so it's possible to get output even in that
case. You can check, without transmitting, for voltage on the
drains of the finals. If there is 12 volts there on Receive then
Q6 is probably shorted, or something in the keying circuits is
making it stay ON. If there is no voltage there on receive, a very
short key up may show some voltage increase on the collector of Q6
which indicates it might be good.
But, the three finals are in parallel and there is no way to test
them individually without pulling them off the board. You can
remove one and test it and if it's good it's possible (not 100%
likely) that the other two are also good. If it's bad then it's
likely that all three are bad.
The easiest way I've found to test components out of the circuit
is with a component tester. I'm not recommending any one in
particular. Here is one that's available
https://www.amazon.com/ACEIRMC-Multi-Function-Pocketable-Multifunctional-Transistor/dp/B08K3BGKXC/ref=sr_1_3?crid=19UMR161OSBJD&dchild=1&keywords=component+tester&qid=1626967926&sprefix=component+tester%2Caps%2C249&sr=8-3
<https://www.amazon.com/ACEIRMC-Multi-Function-Pocketable-Multifunctional-Transistor/dp/B08K3BGKXC/ref=sr_1_3?crid=19UMR161OSBJD&dchild=1&keywords=component+tester&qid=1626967926&sprefix=component+tester%2Caps%2C249&sr=8-3>

Thanks that's helpful.

To be clear to everybody, I fried it out of my own stupidity! I was operating portable from the window of a first floor room where I stay a few days per week for work, the antenna was interfering with the shutters and while trying to sort this out, I unplugged the Z tuner from the QCX by mistake...

Before this, the rig was working well...

73

Yannig - F4IUJ


Re: Fried my qcx+ finals...

Bill Cromwell
 

Hi,

I support what Alan has said, too. I have a couple of radios here with BS170 finals, and with IRF510s. I have accidentally transmitted into open (no antenna at all), very wrong antenna, and even a short a few times. None of them has ever died.  On the other hand, when my "5 watt" radio gives me 3.9 watts with 13 volts on the battery supply I don't waste time with more voltage or massaging inductors trying to exactly 5 watts and especially not to 7 or 8 watts. On the ait=r results will be the same with 3 watts as with 6 watts. I have the same kind of results but with the 510 finals - no pain.

I have seen where some of our list members have tried to squeeze out more power while running the digital modes. You don't need a bad antenna when you over heat the finals. They will fry - literally. One member reports powering his from only 9 volts and two or three watts output - all day long.

Everything affects everything else. The devil is in the details. operate as designed and it should be okay. Sometimes it is not and then questions are more valid than "my QSX fries when I overdrive it with too much voltage for too long".

Most painful mistake, letting the probe slip and accidenatally connect two traces that should *never* meet. Been there-done that.

73,

Bill KU8H

bark less - wag more

On 7/24/21 3:52 PM, Brian George via groups.io wrote:
On Sat, Jul 24, 2021 at 12:22 PM, Alan G4ZFQ wrote:

If you have read the posts here for several years and read what
Hans has said you may realise that is not really true.

I have a "classic" QCX here for 20 metres and have inadvertently transmitted on several occasions with antenna switches in the wrong position or through an ATU on the wrong band. It has survived everything I have thrown at it so my experience very much supports what Alan has said.

73 Brian G3ZOH


Re: Fried my qcx+ finals...

Yannig - F4IUJ
 

On Sat, Jul 24, 2021 at 06:53 PM, VK5EEE wrote:
Lou, if Q6 is blown Open it won't be able to provide DC to Q1,2&3 and will result in no power out. If Q6 is blown Shorted it will provide DC to Q1,2&3 all the time. This may or may not cause problems with the finals as they don't go into conduction until the gates go high so it's possible to get output even in that case. You can check, without transmitting, for voltage on the drains of the finals. If there is 12 volts there on Receive then Q6 is probably shorted, or something in the keying circuits is making it stay ON. If there is no voltage there on receive, a very short key up may show some voltage increase on the collector of Q6 which indicates it might be good.
 
But, the three finals are in parallel and there is no way to test them individually without pulling them off the board. You can remove one and test it and if it's good it's possible (not 100% likely) that the other two are also good. If it's bad then it's likely that all three are bad.
 
The easiest way I've found to test components out of the circuit is with a component tester. I'm not recommending any one in particular. Here is one that's available 
 
Thanks that's helpful.

To be clear to everybody, I fried it out of my own stupidity! I was operating portable from the window of a first floor room where I stay a few days per week for work, the antenna was interfering with the shutters and while trying to sort this out, I unplugged the Z tuner from the QCX by mistake... 

Before this, the rig was working well...

73

Yannig - F4IUJ


Re: Fried my qcx+ finals...

Brian George
 

On Sat, Jul 24, 2021 at 12:22 PM, Alan G4ZFQ wrote:
If you have read the posts here for several years and read what Hans has said you may realise that is not really true.
I have a "classic" QCX here for 20 metres and have inadvertently transmitted on several occasions with antenna switches in the wrong position or through an ATU on the wrong band. It has survived everything I have thrown at it so my experience very much supports what Alan has said.  

73 Brian G3ZOH


Re: Fried my qcx+ finals...

Yannig - F4IUJ
 

On Sat, Jul 24, 2021 at 05:56 PM, Alan G4ZFQ wrote:
Yannig,

This failure is not properly covered in "troubleshooting".

First check for continuity of the LPF with an Ohm meter.

Measure the voltages on Q6, Q1-Q3 both RX and TX.
That may show some clue.

73 Alan G4ZFQ
Thank you Alan for replying,

So i took my multimeter (a digital high impedance jobbie) and went on a measuring spree, here are my findings :

Continuity in LPF : OK (very little resistance across the 3 Toroids in serie)

Tension measurements from the ground taken at the top right corner of the PCB while the 50Ohms load is attached and I made all measures twice, one with the TRX in receiver mode and one while keying the receiver :

  1. BS 170
    • Source always 0V
    • Gate : RX : 0V / TX : 2.57V
    • Drain : RX : 0V / TX : my multimeter refuses to measure it (no Oscilloscope), after keying off I see a very high tension (saw 70V once) then it goes down quickly to a few volts
  2. MPS 751
    • Emitter : RX : 11.89V / TX : 11.5V
    • Base : RX : 11.89V / TX : 10.7V
    • Collector : RX : 0V (after some time) / TX : 11.2V then decreases

I hope this is helpful, sadly I don't have the skills to understand what's going on, any help will be very welcome!

73

Yannig - F4IUJ


Re: Fried my qcx+ finals...

Alan G4ZFQ
 

On 24/07/2021 17:52, VK5EEE wrote:
QCX (and I think in common with many QRP rigs) the "finals" are very sensitive to high SWR
If you have read the posts here for several years and read what Hans has said you may realise that is not really true.
Thousands of QCXs have been built without problems. Hans has tried very hard to destroy the PA without success.
Yes, for some reason it is one of the common faults reported. But in terms of numbers maybe not a high percentage. Obviously not many stay in this group to tell us their QCX has worked without any fault, only those with problems tell us anything.
A good few seem to have been repaired successfully with no recurrence.

True, some seem to have recurrent failures but why just a few?

Quite some time ago protection for class E was discussed, it adds many more components and even then is not foolproof.

73 Alan G4ZFQ


Re: Fried my qcx+ finals...

Albert Tatlock's Greatest Hits - Vol 1
 

On Sat, Jul 24, 2021 at 05:53 PM, VK5EEE wrote:
is there some SWR protection circuit that we can build to include in our QCX?

But how far do you take the QRP Labs kits ?

I've always taken the view that you buy them to form the heart of a project with Hans having done the main
work, and then you add your own stuff to customise / adjust to personal preference. Thats exactly what many
of us have done with his kits for almost 10 years now. (Contrary to popular opinion, I ain't no noob on this group).

If op's want everything included, go buy an Yaesu / Kenwood / Icom / Elecraft and pay for it ;-)

Or if that is not practical is there some circuit we can put in that e.g. has a LED that will light, or not light, if there is mismatch?

Common sense costs nothing when doing tune ups.
Adjust for max rx noise and then final tweaks.
As does not disconnecting the antenna when transmitting.

A simple Hi / low power switch using two fixed regulators would help some users who insist
on using 5w on WSPR and expecting the poor BS170's to survive the heat.

Just about everyone I know of who does WSPR etc says that reducing the power down to about
2.0 - 2.5w maximum is best for the finals.

Swaaaar indicator protection, maybe the old trick of using a 33v zener + LED and small resistance
on the output could be reviewed, which has been a popular hack for many a QRP rig in the past.

I guess many amateur handbooks would reference it.

Seek and you will find...


Re: Fried my qcx+ finals...

 

wonderful thank you in advance Giuseppe

ciao e 73 da Luigi

On 24 Jul 2021, at 17:16, GIUSEPPE <iw8rsb@...> wrote:

hi Louis, could you build ina led probe or meters to control the RF i.  exit, two 1n4148 diodes and a led are enough, I have built several, tomorrow I return home and I give you the photos and the construction scheme.  73 de iu8eun Joseph

Il sab 24 lug 2021, 18:53 VK5EEE <vk5eee@...> ha scritto:
Hello Cher VX Yannig,

QCX (and I think in common with many QRP rigs) the "finals" are very sensitive to high SWR and blow very quickly. If you search some recent posts where i had the same problem you will find much advice. in my own experience in blowing QCX finals many times, it is most likely, hopefully, of only any of Q1-Q3 and/or Q6 to be blown. if you have spare of these the easiest and quickest is probably to replace them and see if it them works, and you can try by replacing one by one, as i did not find a way to test in circuit, but i will post some advice given to me which i followed incorrectly due to my lack of experience and i then actually blew up the entire QCX. So please only if you know what it means below, or if like me you had forgotten how transistors work, some videos to look at to see which is gate etc, will be helpful and how to measure the voltage -- not how i did blowing everything up.

As the blowing of QCX finals is a very frequent thing (at least for me and some others here) i am wondering if there wouldn't be some additional modifications that could be done by us to make some kind of protection? We must remember the QCX is an amazing value rig for all which it contains and Hans the inventor has made incredible job to keep the cost so low and not much profit from each rig, so that we benefit the low cost resembling a rig easily 10 times the price. But these cost savings surely unavoidably come without some things such as: RF gain, filter bandwidth adjustability, CW offset adjustment, high SWR protection, Automatic Gain Control. Yet the experienced electronicians in here know how to do some of those things, so I would like to see what can be done about that. 

is there some SWR protection circuit that we can build to include in our QCX? Or if that is not practical is there some circuit we can put in that e.g. has a LED that will light, or not light, if there is mismatch?  Personally i do keep a SWR meter in line (when i did not i was unlucky) but this also is not a full protection: there are times we do not look at it while transmitting, and an intermittent or slight fault may not show up so well, also we could have as you did WSPR and then we are not present. i really think i should find some way for such protection and it would be good if the experts in here could put heads together to which ways this could be done in an easy and fool proof manner for those of us who build QCX only because of the amazing step by step manual of its construction.

i am not saying you are one of those like me Yannig you may understand these things much better, for myself i passed only for love of CW and memorised most of the electronics, in short term memory at a young age, that RAM was long emptied of most of those electronic things. 

i hope you can fix easily, also there is checking on ic3 voltages after you repair, if you are careful, for me i destroyed also pin 9 which however may not have been important to the operation as it was for BPF set up in the menu, once set up, not needed that menu to be working correctly again. 

Here was one helpful advice when i had same problem as you, but i did not follow it correctly and damaged the entire rig, so i should just have replaced the transistors as i had some spare ones:

Quote

Lou, if Q6 is blown Open it won't be able to provide DC to Q1,2&3 and will result in no power out. If Q6 is blown Shorted it will provide DC to Q1,2&3 all the time. This may or may not cause problems with the finals as they don't go into conduction until the gates go high so it's possible to get output even in that case. You can check, without transmitting, for voltage on the drains of the finals. If there is 12 volts there on Receive then Q6 is probably shorted, or something in the keying circuits is making it stay ON. If there is no voltage there on receive, a very short key up may show some voltage increase on the collector of Q6 which indicates it might be good.

But, the three finals are in parallel and there is no way to test them individually without pulling them off the board. You can remove one and test it and if it's good it's possible (not 100% likely) that the other two are also good. If it's bad then it's likely that all three are bad.

The easiest way I've found to test components out of the circuit is with a component tester. I'm not recommending any one in particular. Here is one that's available 


73 ... Ron

UNQUOTE

also:

QUOTE

On 19 Jul 2021, at 19:14, Arv Evans <arvid.evans@...> wrote:

You can test transistors, and MOSFETS, in several different ways.  
For NPN DC gain you only need to connect the collector through 
470 ohms to Vcc, the base through 4.7k and alternatively through 
470K, and the emitter to ground.  This lets you get an approximation 
of DC gain at the operating voltage and calculated base current.

You can also do an in-circuit test to see if the BE voltage is around 
0.6 volts.

Out-of-circuit tests can use a VOM to see if both B-E and C-B show 
diode action of the proper polarity.  Be sure that your VOM does 
not cause over voltage conditions for either of these junctions.

You can build a free-standing circuit that emulates one stage of the 
circuit it will be operating in inside the rig, and scope that circuit for 
proper operation with similar-to-real-world inputs.

Hang in there.  You are coming along in fine shape.  Soon you will 
be one of the "old timers" who are giving advice to other builders of 
this same equipment.

Arv
_._

UNQUOTE

Good luck and let us know if you need more help there are many here able to assist in the steps. 

73 es 77 de Lou

On 24 Jul 2021, at 15:30, Yannig - F4IUJ via groups.io <yannig.robert@...> wrote:

Hello all,

I'be managed to fry the PA of my qcx (I think) by unplugging the antenna while the tx was in WSPR mode. 

I want to determine with certainty which components to replace and I am not sure that I understand fully the troubleshooting guide... 

So I've determined that the TX now outputs about 200mW in a 50ohms load. What should I do next? 

In advance thank you. 

Yannig F4IUJ


-- 
Love 30m and CW?
http://www.30cw.net




--
Love 30m and CW?
http://www.30cw.net


Re: Fried my qcx+ finals...

GIUSEPPE
 

hi Louis, could you build ina led probe or meters to control the RF i.  exit, two 1n4148 diodes and a led are enough, I have built several, tomorrow I return home and I give you the photos and the construction scheme.  73 de iu8eun Joseph


Il sab 24 lug 2021, 18:53 VK5EEE <vk5eee@...> ha scritto:
Hello Cher VX Yannig,

QCX (and I think in common with many QRP rigs) the "finals" are very sensitive to high SWR and blow very quickly. If you search some recent posts where i had the same problem you will find much advice. in my own experience in blowing QCX finals many times, it is most likely, hopefully, of only any of Q1-Q3 and/or Q6 to be blown. if you have spare of these the easiest and quickest is probably to replace them and see if it them works, and you can try by replacing one by one, as i did not find a way to test in circuit, but i will post some advice given to me which i followed incorrectly due to my lack of experience and i then actually blew up the entire QCX. So please only if you know what it means below, or if like me you had forgotten how transistors work, some videos to look at to see which is gate etc, will be helpful and how to measure the voltage -- not how i did blowing everything up.

As the blowing of QCX finals is a very frequent thing (at least for me and some others here) i am wondering if there wouldn't be some additional modifications that could be done by us to make some kind of protection? We must remember the QCX is an amazing value rig for all which it contains and Hans the inventor has made incredible job to keep the cost so low and not much profit from each rig, so that we benefit the low cost resembling a rig easily 10 times the price. But these cost savings surely unavoidably come without some things such as: RF gain, filter bandwidth adjustability, CW offset adjustment, high SWR protection, Automatic Gain Control. Yet the experienced electronicians in here know how to do some of those things, so I would like to see what can be done about that. 

is there some SWR protection circuit that we can build to include in our QCX? Or if that is not practical is there some circuit we can put in that e.g. has a LED that will light, or not light, if there is mismatch?  Personally i do keep a SWR meter in line (when i did not i was unlucky) but this also is not a full protection: there are times we do not look at it while transmitting, and an intermittent or slight fault may not show up so well, also we could have as you did WSPR and then we are not present. i really think i should find some way for such protection and it would be good if the experts in here could put heads together to which ways this could be done in an easy and fool proof manner for those of us who build QCX only because of the amazing step by step manual of its construction.

i am not saying you are one of those like me Yannig you may understand these things much better, for myself i passed only for love of CW and memorised most of the electronics, in short term memory at a young age, that RAM was long emptied of most of those electronic things. 

i hope you can fix easily, also there is checking on ic3 voltages after you repair, if you are careful, for me i destroyed also pin 9 which however may not have been important to the operation as it was for BPF set up in the menu, once set up, not needed that menu to be working correctly again. 

Here was one helpful advice when i had same problem as you, but i did not follow it correctly and damaged the entire rig, so i should just have replaced the transistors as i had some spare ones:

Quote

Lou, if Q6 is blown Open it won't be able to provide DC to Q1,2&3 and will result in no power out. If Q6 is blown Shorted it will provide DC to Q1,2&3 all the time. This may or may not cause problems with the finals as they don't go into conduction until the gates go high so it's possible to get output even in that case. You can check, without transmitting, for voltage on the drains of the finals. If there is 12 volts there on Receive then Q6 is probably shorted, or something in the keying circuits is making it stay ON. If there is no voltage there on receive, a very short key up may show some voltage increase on the collector of Q6 which indicates it might be good.

But, the three finals are in parallel and there is no way to test them individually without pulling them off the board. You can remove one and test it and if it's good it's possible (not 100% likely) that the other two are also good. If it's bad then it's likely that all three are bad.

The easiest way I've found to test components out of the circuit is with a component tester. I'm not recommending any one in particular. Here is one that's available 


73 ... Ron

UNQUOTE

also:

QUOTE

On 19 Jul 2021, at 19:14, Arv Evans <arvid.evans@...> wrote:

You can test transistors, and MOSFETS, in several different ways.  
For NPN DC gain you only need to connect the collector through 
470 ohms to Vcc, the base through 4.7k and alternatively through 
470K, and the emitter to ground.  This lets you get an approximation 
of DC gain at the operating voltage and calculated base current.

You can also do an in-circuit test to see if the BE voltage is around 
0.6 volts.

Out-of-circuit tests can use a VOM to see if both B-E and C-B show 
diode action of the proper polarity.  Be sure that your VOM does 
not cause over voltage conditions for either of these junctions.

You can build a free-standing circuit that emulates one stage of the 
circuit it will be operating in inside the rig, and scope that circuit for 
proper operation with similar-to-real-world inputs.

Hang in there.  You are coming along in fine shape.  Soon you will 
be one of the "old timers" who are giving advice to other builders of 
this same equipment.

Arv
_._

UNQUOTE

Good luck and let us know if you need more help there are many here able to assist in the steps. 

73 es 77 de Lou

On 24 Jul 2021, at 15:30, Yannig - F4IUJ via groups.io <yannig.robert@...> wrote:

Hello all,

I'be managed to fry the PA of my qcx (I think) by unplugging the antenna while the tx was in WSPR mode. 

I want to determine with certainty which components to replace and I am not sure that I understand fully the troubleshooting guide...

So I've determined that the TX now outputs about 200mW in a 50ohms load. What should I do next? 

In advance thank you.

Yannig F4IUJ


--
Love 30m and CW?
http://www.30cw.net


Re: Receiver front-end filter #rcvr

Glen Leinweber
 

Ton,
Yes, Hans would be less-aghast at tiny hyper-abrupt varicaps than that monster
dual-gang variable capacitor - as Cristi points out, its size compares with the
whole receiver module!
The physical scale of Hans designs amazes me - his board layout is as crowded
as a rush-hour bus on this receiver module.
In general, electronic design trends toward microscopic size where robots
out-perform shaky human hands. Hans obviously uses CAD to design his boards,
using component placement tools effectively. My industrial PCB layout days were
with tape & vellum on a drafting table, when half-watt resistors were standard, and
generally lay flat: double-sided boards with plate-thru holes were exotic.

I'd want to do some careful IP3 measurements when substituting varicaps for that
very linear mechanical variable capacitor. If any large unwanted signals sneak in,
they'd cause spurious mayhem. The Tayloe mixer in these radios is well-renowned
for its spurious rejection. Why taint it with a potentially weak pre-filter?

Be aware that this tune-able filter does make compromises that the QRP-Labs
fixed-tuned band filter modules avoid. As stated, bandwidth at the high-frequency
end of the tuning range is very wide, with inferior stop band attenuation.


Re: Fried my qcx+ finals...

 

Hello Cher VX Yannig,

QCX (and I think in common with many QRP rigs) the "finals" are very sensitive to high SWR and blow very quickly. If you search some recent posts where i had the same problem you will find much advice. in my own experience in blowing QCX finals many times, it is most likely, hopefully, of only any of Q1-Q3 and/or Q6 to be blown. if you have spare of these the easiest and quickest is probably to replace them and see if it them works, and you can try by replacing one by one, as i did not find a way to test in circuit, but i will post some advice given to me which i followed incorrectly due to my lack of experience and i then actually blew up the entire QCX. So please only if you know what it means below, or if like me you had forgotten how transistors work, some videos to look at to see which is gate etc, will be helpful and how to measure the voltage -- not how i did blowing everything up.

As the blowing of QCX finals is a very frequent thing (at least for me and some others here) i am wondering if there wouldn't be some additional modifications that could be done by us to make some kind of protection? We must remember the QCX is an amazing value rig for all which it contains and Hans the inventor has made incredible job to keep the cost so low and not much profit from each rig, so that we benefit the low cost resembling a rig easily 10 times the price. But these cost savings surely unavoidably come without some things such as: RF gain, filter bandwidth adjustability, CW offset adjustment, high SWR protection, Automatic Gain Control. Yet the experienced electronicians in here know how to do some of those things, so I would like to see what can be done about that. 

is there some SWR protection circuit that we can build to include in our QCX? Or if that is not practical is there some circuit we can put in that e.g. has a LED that will light, or not light, if there is mismatch?  Personally i do keep a SWR meter in line (when i did not i was unlucky) but this also is not a full protection: there are times we do not look at it while transmitting, and an intermittent or slight fault may not show up so well, also we could have as you did WSPR and then we are not present. i really think i should find some way for such protection and it would be good if the experts in here could put heads together to which ways this could be done in an easy and fool proof manner for those of us who build QCX only because of the amazing step by step manual of its construction.

i am not saying you are one of those like me Yannig you may understand these things much better, for myself i passed only for love of CW and memorised most of the electronics, in short term memory at a young age, that RAM was long emptied of most of those electronic things. 

i hope you can fix easily, also there is checking on ic3 voltages after you repair, if you are careful, for me i destroyed also pin 9 which however may not have been important to the operation as it was for BPF set up in the menu, once set up, not needed that menu to be working correctly again. 

Here was one helpful advice when i had same problem as you, but i did not follow it correctly and damaged the entire rig, so i should just have replaced the transistors as i had some spare ones:

Quote

Lou, if Q6 is blown Open it won't be able to provide DC to Q1,2&3 and will result in no power out. If Q6 is blown Shorted it will provide DC to Q1,2&3 all the time. This may or may not cause problems with the finals as they don't go into conduction until the gates go high so it's possible to get output even in that case. You can check, without transmitting, for voltage on the drains of the finals. If there is 12 volts there on Receive then Q6 is probably shorted, or something in the keying circuits is making it stay ON. If there is no voltage there on receive, a very short key up may show some voltage increase on the collector of Q6 which indicates it might be good.

But, the three finals are in parallel and there is no way to test them individually without pulling them off the board. You can remove one and test it and if it's good it's possible (not 100% likely) that the other two are also good. If it's bad then it's likely that all three are bad.

The easiest way I've found to test components out of the circuit is with a component tester. I'm not recommending any one in particular. Here is one that's available 


73 ... Ron

UNQUOTE

also:

QUOTE

On 19 Jul 2021, at 19:14, Arv Evans <arvid.evans@...> wrote:

You can test transistors, and MOSFETS, in several different ways.  
For NPN DC gain you only need to connect the collector through 
470 ohms to Vcc, the base through 4.7k and alternatively through 
470K, and the emitter to ground.  This lets you get an approximation 
of DC gain at the operating voltage and calculated base current.

You can also do an in-circuit test to see if the BE voltage is around 
0.6 volts.

Out-of-circuit tests can use a VOM to see if both B-E and C-B show 
diode action of the proper polarity.  Be sure that your VOM does 
not cause over voltage conditions for either of these junctions.

You can build a free-standing circuit that emulates one stage of the 
circuit it will be operating in inside the rig, and scope that circuit for 
proper operation with similar-to-real-world inputs.

Hang in there.  You are coming along in fine shape.  Soon you will 
be one of the "old timers" who are giving advice to other builders of 
this same equipment.

Arv
_._

UNQUOTE

Good luck and let us know if you need more help there are many here able to assist in the steps. 

73 es 77 de Lou

On 24 Jul 2021, at 15:30, Yannig - F4IUJ via groups.io <yannig.robert@...> wrote:

Hello all,

I'be managed to fry the PA of my qcx (I think) by unplugging the antenna while the tx was in WSPR mode. 

I want to determine with certainty which components to replace and I am not sure that I understand fully the troubleshooting guide...

So I've determined that the TX now outputs about 200mW in a 50ohms load. What should I do next? 

In advance thank you.

Yannig F4IUJ


--
Love 30m and CW?
http://www.30cw.net


Re: Fried my qcx+ finals...

Alan G4ZFQ
 

I'be managed to fry the PA of my qcx (I think) by unplugging the antenna while the tx was in WSPR mode.
So I've determined that the TX now outputs about 200mW in a 50ohms load.
Yannig,

This failure is not properly covered in "troubleshooting".

First check for continuity of the LPF with an Ohm meter.

Measure the voltages on Q6, Q1-Q3 both RX and TX.
That may show some clue.

73 Alan G4ZFQ


Fried my qcx+ finals...

Yannig - F4IUJ
 

Hello all,

I'be managed to fry the PA of my qcx (I think) by unplugging the antenna while the tx was in WSPR mode. 

I want to determine with certainty which components to replace and I am not sure that I understand fully the troubleshooting guide...

So I've determined that the TX now outputs about 200mW in a 50ohms load. What should I do next? 

In advance thank you.

Yannig F4IUJ


Re: Receiver front-end filter #rcvr

Ton - PA0ARR
 

You can also use some varicap diodes on the standard bpf boards.
73 de Ton

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