I have been playing around with a project for a while and have brought it to a point where it works well enough to post.
Its a simple AM radio with one valve that can be built by anybody.
It uses parts that can be easily obtained from Jaycar, ebay and the junk box.

I have used the Dekal 6Y9/EFL200 double pentode.
The design first followed the good 1950's grid leak + reaction theme but changed a bit as you will read.
Why would you build this?
Because you can!
I would dearly like some other enthusiasts to knock up their version of it, just for fun and to learn a bit.
There will be improvements in the future to increase the performance of the basic build.

Why do I call it the 'Resonator'?
Every project needs a spiffy name, AND, thats what coils do!

Fred.

VR Resonator Project - Part 1
VR Resonator Project - Part 2

A bit of 'errata' for this project.
In the text I got a bit muddled up with the wire size for the tuning coil.
The final coil uses 0.036 or 0.9mm wire, NOT 0.018 .7mm

Fred.

So annoyed at the moment.
Some time ago I found a 10 pin valve socket, and a couple of NOS 6Y9's.
Put aside for a previous project using 6Y9.
Do you think I can find it now, I'm sure its safe but that does not help.......
Will hard wire it if necessary, go Fred.
JJ

Document uploaded.

Next on this project, I have upgraded the Mk1 to a MK2.

The basic project is the same but with another coil added to sharpen up the selectivity.

I'll send a PDF to pin to post 1.

The added coil makes the set a bit calmer to tune and use.
There is an extra "AGC" loop in the audio section that helps that.

I'll look at a cabinet and a progression in the build later.

I will be thrilled if anybody has a go at duplicating the build!

PDF for the Mk2 sent to Brad.

Fred.

Part 2 uploaded.

Neat, Fred!

Those valves had much shorter lives in service than earlier types. A 2nd hand 6Y9 would be highly suspect! Internal flashovers were common. And the other members of the family weren't much better. It does pay to under-run them we found but reducing the B+.

I think the guys at Pye knew this when they skipped the 10 pin bottle generation entirely and went straight to Fairchild silicon transistors for the T23.

Did you consider connecting AGC to the front end?

Hi Ian, yes I did trial AGC to the first coil but it never made it to the final version.
For some reason the range of control was pretty ineffective and I never pursued it to find out why.

The next step is to re-jig the front end to receive FM.

I have made a valve FM receiver previously.
That was ages ago in the form of a Superhet using a 6AM6 as the front end valve and a bunch of 6BX6 doing all sorts of things with a 10meg IF.. It worked very very well and taught me a lot about working at 100meg.
I see all sorts of doozy ideas from the 1960s on wards in hobby magazines like RH, WW, on the net and so on with 'super regen' screamers.
No, i'm having an RF stage and a diode demodulator and thats it.

Impossible? we will see.

Cheers, Fred.

Super-regen should be possible, but they are horrible, cranky things!
Look up the RTV&H Fremodyne..

An automatic regen system has always interested me.
Perhaps split the detected audio and feed one side into dc filtered circuit and that then controls somehow the amount of regen applied.
And be partially adjustable and still similar to an AGC system.
Hmm.....JJ

I've done the first step and connected the first pentode of the 6Y9 as a triode and hooked a 4 turn coil across the grid to cathode.
I'm following the work shown on the "Cool" web site with 6C4, 12AT7 and so on Regen FM receivers described.
The 6Y9 does actually work and I can receive the local FM stations with no antenna connected at all!
Lots of technical problems but the regeneration theory as described in the 1929 to 1949 textbooks does work amazingly well.
I'll post up progress this week.

Fred.