Late 1960's BFO

[HECTOR]

L2 value incorrect, R12 value is 68K, screen on coil, and can on 10mm inductor not shown. It's worth pointing out that the audio output transformer doesn't need its output tied to 0V ground, it would track easier on a PCB if it were joined to +9V, I don't see why it couldn't be left isolated, either. I said I had printed datasheets for Toko 10EZ coils (Bonex/BEC/Cirkit catalogues), well I've found the same ones online recently, here's the link:http://pe2bz.philpem.me.uk/toko_coils/10ez.pdf.zip

Thanks again Skippy and Jap!
Thought I changed R12 a long time ago...guess not.
Once this schematic gets approval by you guys, (it runs on the program now and even asks for more info to display waveforms) then I would be happy to try any mods that you see fit on my working unit.
I think the first thing that I'll try will be to isolate the audio output as suggested.

[jap]

Hi HECTOR
you - arrived to full,but there one mis. in your modified pictur!!!!!!!
Good work.
best time.
j.

[Skippy]

L2 value incorrect, R12 value is 68K, screen on coil, and can on 10mm inductor not shown. It's worth pointing out that the audio output transformer doesn't need its output tied to 0V ground, it would track easier on a PCB if it were joined to +9V, I don't see why it couldn't be left isolated, either. I said I had printed datasheets for Toko 10EZ coils (Bonex/BEC/Cirkit catalogues), well I've found the same ones online recently, here's the link:http://pe2bz.philpem.me.uk/toko_coils/10ez.pdf.zip

[HECTOR]

Spent some time correcting what I think are all the errors.
Has interest died on this? Is anyone going to play with it besides me?
This one here.

[jap]

friends

Hi HECTOR
In a few words all what you put all reading a - must trust - right everyone knows - so we are friends - let's go back to the Thread.
best time.
j.

[HECTOR]

Hi HECTOR
I hope you can say thank you to Gwil Because he gave shape and repaired some mis.
-Re:there are two mis. in your modified pictur!!!!!!!
best time.
j.

Honoring an example of his layout is not saying thanks? Of course I can say thanks Gwil!

To me, a finger print on the window is as the shade pulled down for you.
I would need to study oscillator theory and schematics for a good 50 hours to come close to spotting mistakes as easily as you do
Never needed to get into oscillators when repairing pro audio amplifiers. If an oscillator power supply fails, a cap or two usually gets it up and running.

THANKS! ALL OF YOU GUYS FOR CONTRIBUTING TO THIS PROJECT!!

I'm actually learning some stuff!
Thank you VERY much Jap!

OK Jap...where are the errors now?

[jap]

Hi HECTOR
I hope you can say thank you to Gwil Because he gave shape and repaired some mis.
-Re:there are two mis. in your modified pictur!!!!!!!
best time.
j.

[HECTOR]

Hi Hector

It might be worth redrawing the circuit in this sort of layout, only neater and without any errors I may have added:

Like this?

[HECTOR]

Bring it up in Circuit maker and take a Photograph of it.
I find on these newer LCD screens, Photos come out pretty clear.

That's what I have been doing. Not a photo, I just make a graphic copy in jpeg.
It would be so much easier if I could present a ckt file so it could be manipulated within the Circuit Maker program. Otherwise, I may as well try to finish the updated schem myself, Thought one of you guys could do a faster, better job than me

[chemelec]

Anybody know how to transfer ckt files from Circuit Maker? Was hoping one or more of you aces would be willing to snaz up that schematic

Bring it up in Circuit maker and take a Photograph of it.
I find on these newer LCD screens, Photos come out pretty clear.

[HECTOR]

I've just had another study of my Toko datasheets, to pin down construction details of the 10mm can inductor. Though Hectors coil is not a Toko coil, I think it will be similar to Toko's 10E and 10EZ range, commonly used in 455KHz IF stages in radios. The inductance of these cores is determined by the number of turns and the specific inductance,AL (big A, little subscript L).

Inductance = AL x (number of turns)squared

Analysing the data for a number of these coils, it seems that AL is close to 25 nH for the 10E core. From this, to make a 60 microhenry coil for this project, we need 49 turns of wire. Commonly, 455KHz coils/transformers will have around 170 turns, so it should be possible to salvage enough wire to rewind them for this project, but Q would be improved if slightly thicker wire were used, or you may be able to rewind the original wire bifilar. These cores have a wide adjustment range, possibly +/-20%, so number of turns is not too critical.
I also have data for 7mm and 5mm coils if anyone fancies miniaturising it, eg. for pinpointer use.

Thanks Skippy
I have an old analog, vacuum tube L/C meter in my sights on ebay. Was looking at those $18 China ones on ebay. Don't like dealing with China on ebay. Too many crooked players so I'd rather not give them any biz.
Was thinking that would save guess work, if I had a meter.
Am pretty serious about making a pinpointer out of it. Just did some more modding on my CenTech. Added a second vibrator with an LED in between and disconnected the speaker. Would like to do away with the sens changes when the temp changes.
Have had it out on sunny mornings, set perfectly, and by noon, it's going off by its self
I think that building some coils will be in my future projects.
There have been several times I'd wished that I had an inductance meter.

Anybody know how to transfer ckt files from Circuit Maker? Was hoping one or more of you aces would be willing to snaz up that schematic

[Skippy]

I've just had another study of my Toko datasheets, to pin down construction details of the 10mm can inductor. Though Hectors coil is not a Toko coil, I think it will be similar to Toko's 10E and 10EZ range, commonly used in 455KHz IF stages in radios. The inductance of these cores is determined by the number of turns and the specific inductance,AL (big A, little subscript L).

Inductance = AL x (number of turns)squared

Analysing the data for a number of these coils, it seems that AL is close to 25 nH for the 10E core. From this, to make a 60 microhenry coil for this project, we need 49 turns of wire. Commonly, 455KHz coils/transformers will have around 170 turns, so it should be possible to salvage enough wire to rewind them for this project, but Q would be improved if slightly thicker wire were used, or you may be able to rewind the original wire bifilar. These cores have a wide adjustment range, possibly +/-20%, so number of turns is not too critical.
I also have data for 7mm and 5mm coils if anyone fancies miniaturising it, eg. for pinpointer use.

[homefire]

Some of the Old BFO used Copper Tubing for Shielding on the coil.

[Skippy]

I felt that the foil screen was a bit excessive, and probably reduced sensitivity. I think a graphited-paper or similar screen would help a bit, and it would be worth trying on your circuit. One problem I found with the EPE circuit is the sensitivity to hand capacitance on the RC oscillator/pot area, it needs to be shielded well. It's also not stable thermally, amongst many other shortcomings.

[HECTOR]

Why is R12 still shown as 60K? Obviously, we don't have any views of the components that enable us to see this part, but it has to be something different, like 68K? Maybe the colours have faded or something, I suppose you could ultimately remove one leg and measure it with a meter.....
I think ferrite cores are unsuitable for BFO coils, they are very temperature sensitive. A suitable size for an air-cored coil,to start with is 35 to 40mm diameter. I suggest you take a look at the Scarborough EPE magazine mini-pinpointer design for ideas. I've made a 35mm coil for that, with self-adhesive foil screen. It would find a 25mm copper coin at 30mm distance.
http://david.alfa-romeo.eu/elektro/EPE/2003/EPE%202003-07.pdf

R12 is a 68K (65.5 to be exact)
Thanks for the link. That's a simple, compact unit. A wristband mount and a finger mounted coil would be slick. I'd like to hear what it sounds like.
I found that if I make about a 20MM 40 turn coil and split it, then I can move the two pieces to tune. It reacts to a quarter at about 25MM. Will it make a big difference if I shield it carefully? I like the way the tone varies with proximity.
My CenTech pinpointer is either off or on. Has anybody around here broken into one of those yet?