FET GDO Problem

Thread Starter

AlbertHall

Joined Jun 4, 2014
12,625
I built the circuit below. It doesn't oscillate. The DC conditions seem wrong. I measure 2V at Q1 and Q2 source and also at Q3 source (this is with 3V supply).
There is no short circuit between Q3 source and drain.
Are these voltages incorrect and what should I check?


Original Circuit.jpg
 

Thread Starter

AlbertHall

Joined Jun 4, 2014
12,625
Hello,

The schematic seems to be from the ARRL handbook.
I have copied the pages related.

Bertus
That ciecuit is shown with three batteries and from the article "The prototype was constructed with two batteries but three result in better operation."
Maybe that would make the difference?
 

MisterBill2

Joined Jan 23, 2018
27,501
I saw it in a QST article first, before the handbook. Source and drain are not identified at all in the circuit drawing. AND the sense coil is also a DC path. so there is an additional consideration.
 

sparky 1

Joined Nov 3, 2018
1,218
I liked the 1250 Dip meter. The assembly is difficult. This manual was so detailed that you might worry about the details. In the pdf, some hobbyist
of that Era considered Heathkit manual "the secrets" that were abbreviated in magazines, fixing an MFJ and why it's called a swear meter.
It was also built like a tank like GD1 and mechanical assembly small but not as bad as a cell phone. Not just a simplified circuit or simulation.
The Manual for the Heathkit HD-1250 DejaVu Document page 60 circuit board day 3 and lessons of patience of the watchmaker the project truth.

In the video some techniques that a ham clubs used to demonstrate. If you spot the Ten Tec that was possibly the better Radio kit in those days.


Climbing up a tower, is for very experience Telecom, that are in good shape, but what is inside a 1998 MFJ-259B compared to Nano VNA?
Somebody may have modified the low band for 300Ω, like bird ladder. What would the numbers look like with 40Ω load? how about a Z match?
There are Z match for Transmitters under 15Watts that cost only $30 these might give you 1.2 SWR the 1.6 Jpole before trimming.
 
Last edited:

MisterBill2

Joined Jan 23, 2018
27,501
There are a few errors that have been propagated in ARRL publications forever. Some places it shows that there has been no technical proofreader.
Overall the quality is rather good, but not perfect.
In this dipper case, certainly the wide spread of Idss probably makes a difference. And the lack of markings for source and drain also. It does matter quite a bit.
 
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