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QMX Using Z-Match ATU Blown Finals -- Twice

 

I've used variations pretty much the same Z-Match tuner for many years.
Since the first NorCal BLT

Wasn't trying to get more power, just reducing the reflected RF for better SWR.
Supply voltage was 13.6 and band was 20 m.?

I don't recall exactly what happened the first time. But it was when I switched from
Adjust to Operate.? One suggestion was to reduce power and don't hot-switch.
I don't think I hot-switched. Another suggestion was an inductive spike.
Anyway, sent it off, got it fixed, and the same thing happened again. This time
supply voltage at 9, 30m, and I know I didn't hot switch. Also adjusted for noise
peak first.



I've used this tuner with everything from Rock-Mites to a uSDX+ with no problems. uSDX finals are
similar to the QMX, I think.? Used the same setup with the uSDX right after and no problem.?

Clueless in the suburbs of Point and Emory, Rains Co., Texas? EM22cv.


Chuck, W5USJ
EM22cv, Rains Co., Texas

 

Hi Chuck,

Sorry to read of your problem.??

I believe that the QMX has an SWR function that is at reduced power.? It might be better to use it to adjust the Z-Match.? That would give you an easier-to-read number rather than an LED intensity.

Just a suggestion/
73
Evan
AC9TU
 

Try using 12v rather than 13.6v. ?They are not the same for QMX purposes.
 

Further info: The QMX, like the QDX power, will change with the impedance.? I have noted an increase in power ratings for SWRs that, when I put it on a dummy load, are 1.5 watts or more lower.? This could happen while you are adjusting for the LED dip.

73
Evan
AC9TU
 

Evan,
I had Vcc at 9V this last time. I think the power with WM-2 and dummy load was about 1.2W
Next I switched to antenna with tuner in adjust mode. The bridge is about 1.5:1 SWR.
The failure happened when I switched to operate mode.

--

Chuck, W5USJ
EM22cv, Rains Co., Texas

 


--Ooops, the power meter was between the QMX and the Tuner

Chuck, W5USJ
EM22cv, Rains Co., Texas

 

I’m surprised more people haven’t mentioned this… But if your QMX is built for 12 V you should never apply more than 12 V.
If your QMX was built for 9 V you should never apply more than 9 V.
It’s fairly easy to damage your finals if you apply more power than 12 or 9 V depending on the build voltage.
 

It's been mentioned many times in this group. I have a power cord with a buck converter to keep my 12V QMX fed with 11.5V.

Brian
n1bs

On Sat, Mar 2, 2024 at 9:44?AM Howard Lamhut <Howardlam@...> wrote:
I’m surprised more people haven’t mentioned this… But if your QMX is built for 12 V you should never apply more than 12 V.
If your QMX was built for 9 V you should never apply more than 9 V.
It’s fairly easy to damage your finals if you apply more power than 12 or 9 V depending on the build voltage.
 

The second failure was with Vcc at 9V. Power at about 1.2W.? Last sentence of the first paragraph.

--

Chuck, W5USJ
EM22cv, Rains Co., Texas

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