[Boatanchors] Improving the Novice "Two Tube Beginner's Receiver"

[whitebear1122 at comcast.net]

That beginners regen receiver in the ARRL "How to Become a Radio Amateur"
has been on my list of things to build since I first read the book in 1966.
I've kept that publication for all these years.  Thanks for the notes on the
bandset fix.  I just printed it out and will slip it in the book so it's
there when the time comes to build.   While I don't have the National Type K
vernier dial they used, I did find a Type M which looks the same but is a 5"
diameter stainless steel dial.  Out of sheer nostalgia, I plan to build this
radio so it strongly resembles the one in the article.  I'm not expecting
much in the performance department but we'll see.  

Thanks Dave!  73 Scott WA9WFA

-----Original Message-----
From: boatanchors-bounces at mailman.qth.net
<boatanchors-bounces at mailman.qth.net> On Behalf Of David Stinson
Sent: Sunday, January 1, 2023 6:53 AM
To: Boatanchors at mailman <boatanchors at mailman.qth.net>; Boatanchors at ThePorch
<boatanchors at lists.theporch.com>
Subject: [Boatanchors] Improving the Novice "Two Tube Beginner's Receiver"

How many of us remember or even built this simple 2-tube regen from this
book?  I'll bet some of you still have one on the shelf or in the attic. 
   It's a simple and fun circuit and taught one how to make the most of a
simple regen.

https://photos.app.goo.gl/6mkuXKN18UjjWhkw5
https://photos.app.goo.gl/cDJybxoUSj1oyQDH8

  However, it has one design flaw which, once corrected, makes it much
easier to use.
In the piece, the "Band Spread" capacitor, C1, sets the frequency the set
tunes from one end of the tuning cap to another.  In order  to "spread it
out" to a usable range- say, from 7000 KC to 7100 KC, one moved the coil tap
which connected C1 to the tuning coil, moving the tap up toward the "hot
end" of the coil.

https://photos.app.goo.gl/aepZMY8JcitTsCNo9

The value of C1 works well on 160 or 80 meters, but there is a problem with
this if one is using it on 40 meters or higher:  The higher one moves the C1
tap on the tuning coil, the harder it is to get stable regeneration.  This
is because as the 140 pFd C1 moves higher on the coil, it begins to act not
only as a tuning capacitor, but also as an RF Bypass, draining energy from
the tank circuit to ground and lowering the tank Q.

We can fix this.  First, put the C1 tap back where the author first said to
put it.  Use an RF-quality, NP0 100 pFd cap in series with C1, mounted on
the 40 Meter coil between pin 3 and the "bandspread" tap, effectively
reducing the "Bandspread" cap to a lower value and reducing its bypassing
and Q-killing problems.  You'll find you have good bandspread without the
difficulty getting enough regeneration.  If you're using your set on 20 or
15 meters, reduce the series cap value until you get the bandspread range
you need.
Note:
Don't use those "blue dipped"  Chinese caps from Amazon.
They are useless junk at RF

GL IN 23 OM ES 73 DE Dave AB5S