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

[David Stinson]

I wasn't quite clear.  C1 is the "bandspread" cap but it's also the main 
tuning cap.  C2 is "band set."

On 1/1/2023 6:52 AM, David Stinson via BoatAnchors wrote:
> 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
> 

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