True to Norms design, except for a couple minor components, it's built with totally junk box items... Chassis has built in coil form... Worked first time out the gate...

Must have some parts that are too new, can only receive Radio Disney @ 1650 and one other station very weakly... Guess I need to learn a bit more about building regens...

Tom

Edited to allow pict as link to save load time...

http://members.cox.net/35z3/12k5a.jpg

http://members.cox.net/35z3/12k5b.jpg

Well, I can't help you out with the radio Disney problem, but that's definitely a great use for CD containers. Nice work Tom!

Clever use of a DVDR/CDR cake pan.

Does it regen? That is can you advance the regen control far enough that it oscillates?

RCW

Hi RC

Yes it will oscillate, develops a healthy squeal with pot more than 3/4 advanced... Guessing the coil isn't optimum, the 1650 station comes in in the middle of the tuning cap, planning on removing a few windings...

Also I can light off my xmitter on 1500 and it will separate the two, so I have little doubt it's working...

Tom

Very good.

Now all you have to do is play, have fun, and make it work the way you want.

That is truly the fun part, I used to spend hours, once I had a receiver working, tweeking this and messing with that.

Just playing until it was just right..... and then wondering what I could do to make it better

I think my love of electronics has kept me with it since 1947, earned me a good living and retirement.

I still enjoy my lab today.

RCW

Tom,
Is your tuning cap 365 pf?

Also your coil, you'll probably need more then 100 turns on that
small form. I know that 90 turns on a 1.25" form works and about
100 turns on a 1" form.

Other wise it sounds like you got a winner!

John
KB7NRN

Hi John

Cap is approx 300pf with both sections in parallel... Figured since we really have nothing below 790 locally, it wasn't going to make a big difference...

I suspect you're correct on the coil... I disconnected the top to add a few windings(after I removed a few) and the super glue broke loose, as I'd only tacked the first couple coils... Can you say mini slinky??? LOL ... Anyway I tried one of the 6BM8 xmitt coils I'd wound and get similar results, except it goes into oscillation at a much lower setting of the pot...

I'll try your suggestion, at least with the center spindle, I can set a larger form over it...






You guys like that HUH??? Suspected I catch some flack, asking if couldn't at least scrounge up a piece of 1" by...



Tom

Awesome, dude! Might have to try that myself. They've got some really tall CD-R packs at church. Will have to see if I can get one of those- might be able to mount the speaker on the top of one of those and make it entirely self contained except for the antenna and wall wart.

Scott Todd

Hi Scott

My original intention was to mount the socket on top of the spindle, and have it fully enclosed... About the time I had the coil wound, I realized that was a bad plan...

Biggest drawback is it has to be built in two sections then final connections made from the opening(both connections to cap, and tickler as well as connection to tube socket... I suppose the components could be mounted on the base and use extension shafts for the cap and pot...

Tom

Best configuration so far, larger coil with approx 95 turns(had to remove a few was at 100+)... Will tune from 1650 down to approx 750 with my 300pf cap, suspect that's as good as it gets... Still trying to figure out the regen(note tickler) but have now received five stations...

Tom

So, how's the audio? Enough to drive a speaker?

John
KB7NRN

See next post...

I've worked with it a bit more(tried approx 10 different xformers) and made a significant improvement in audio level... It's gone from "yeah I think I can hear it" to a listenable volume at 6-8 ft... Still not exactly the thing for listening to "The Boot Scootin' Boogie" but not bad... Speaker is a 16 ohm 2"x4"... Same song was playing in all pix, I have no way to use a tone except with a xmitter and the RF distorts the waveforms...

All shots with scope set at .05v and 10x probe... Voltage taken at speaker...

First shot is my original output xformer from battery port... Note distortion...



Second shot is with my famed 25v power xformer used in the 25L6 xmitter... A 18v door bell xformer came close, but had distortion no matter how it was connected(see also third pix)... Biggest issue is I now have about 3lb of iron connected to a 6oz receiver... Small 12/15v secondary xformers were not nearly as good as the 25v job..



Same xformer as above but speaker leads reversed... Makes noticeable difference in audio...




Tom

I tried a doorbell transformer once, but it had a serious ringing problem.

Mine musta been for a buzzer...

Tom

Use a fairly low resistance output transformer. I used a 70 volt to line type which has different taps. A transformer designed for 50C5 or 50L6 will also work. Need low resistance as the tube draws around 40 ma plate current but only has 12 volts to work with. Don't want to drop much voltage.

I used an 8" radio speaker. It matched well with the transformer I was using.

Adjust the regen control just below the point of oscillation. Turning it up the radio goes into oscillation. Back off the control until it stops. Then turn it up again until just that point. The control is critical in getting max volume.

I live 30 miles or more from the closest radio stations. Still able to get several station. I wouldn't want it any louder in a room.

Use 10 feet or so of antenna wire. Be sure you have a ground. Most wall warts don't have a cap between supply voltage and AC line. I added one for ground.

Have you tried modern phones? You don't need 2000 ohm type. Max volume on phones was too loud for me.

For those that know 1 tube (1 section) radios most are only listenable on phones and not very loud.

On a scope was suprised to see a several volt signal on grid of the 12K5. This is caused by regen.

Hi Norm

I tried a AA5 xformer... While it was better than the 3V4 output, wasn't nearly as good as the 25v one(BTW the CT was almost identical in performance)... Been to cold to do much though, I'll try a larger speaker and run the transformers through it again when it warms a bit... Possibly a 8 ohm speaker will require a different piece of iron...

Tom

Did a little more work... Mostly to cold, hope it warms up some...

Using a 5" speaker from a small table top stereo system, I now have enough volume to be plenty listenable in the average size room... Key is a low primary impedance xformer(a AA5 xformer just doesn't cut it)... Upon checking some car radio schematics, I found most that use the 12K5 have a resistance of 50 to 160 ohms... So at the moment I have a 26v @ 1a power xformer that has 43ohm pri and a 1.3 ohm sec... Works nice... Probably going to hit up the old car radio that supplied the 12K5 for it's xformer...

Need to do some tweaking on the tickler, having issues with being able to get good regen action at opposite ends of the dial... Confident I'll get it worked out though...

Looks like Norm has another winner, someone with a little regen experience should not have difficulty building a "hot" player...

Tom

Tom- Norm has never come up with a "dud". He is probably the most knowedgeable person here on the forums when it comes to tube technology. How many other people can you think of who have come up with circuits using otherwise unknown tubes to work fine in some off-beat circuits?
Curt