Re: PA question

J68HZ
 

Good progress Patrick!


Dr. William J. Schmidt - K9HZ J68HZ 8P6HK ZF2HZ PJ4/K9HZ VP5/K9HZ PJ2/K9HZ

 

Owner - Operator

Big Signal Ranch – K9ZC

Staunton, Illinois

 

Owner – Operator

Villa Grand Piton - J68HZ

Soufriere, St. Lucia W.I.

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email:  bill@...

 


On Feb 28, 2017, at 11:33 AM, patrick.nairne@... wrote:

Well the cause of my problems turned out to be a solder bridge between C2 and the R1 wiper made when I replaced the trifilar . The PA is now producing and output, although on both 24Mhz and 14Mhz bands I can only see around 2 watts into a dummy load as I advance R1. Beyond a certain point the output starts to drop, as expected. The heatsink gets hot quite quickly. Another mystery at the moment, connecting the envelope control signals kills the signal, so something else to investigate.
Thanks again for your help.
 
Patrick M0AFZ
 
From: patrick.nairne@...
Sent: Monday, February 27, 2017 1:35 PM
To: QRPLabs@groups.io
Subject: Re: [QRPLabs] PA question
 
Hi Christan
My comment about seeing no voltage on Q7 was before I discovered that I had wired the Trifilar wrongly. Since correct placement I now see voltages. however, it seems my replacement pot is faulty, and I have to find another.
R20 is correct.
I’ll report back when I have a working R1 pot.
Thanks to you and William.
 
Patrick M0AFZ
 
From: Christen Fihl
Sent: Monday, February 27, 2017 7:29 AM
To: QRPLabs@groups.io
Subject: Re: [QRPLabs] PA question
 

Patrick, you did write 2 days ago, that: No voltage seen on Q7 whatever the position of R1.

That is not correct behaviour.

Also you say that R1 gets smoking. Not correct either, as R20 being 3.3K limits that.

Sounds like the slider of R1 is shorted to something, likely ground, as smoke gets there when you turn the slide very close to +5V end. Also do check that R20 is 3K3 = orange-orange-black-BROWN-brown, and not 330ohm.

 

Normal behaviour, and easy testing, is

Step1: Do measure total current to whole PA, and while current is below 100mA try to raise R1 somewhat, like until max halfway.

Step2: Put R1 slider turned one fifth. (No smoke? Check) Now measure voltage on slider. It is 1 Volt. Has to be about there, not zero, not 5V. And also measure Gate voltage on Q7. Has to be exactly the same as on slider. That is,both ends of R20 has 1Volt.

PS: Step2 can as well be done without Q7 mounted, just to check that the rest of the wiring is correct.


73 Christen Fihl, OZ1AAB

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