Home Broadcaster Part 2

Let's select some transistors and build up the little AM Broadcaster.

[@acestudioscouk-Ace-G0ACE]

Learning about PNP and positive ground was an interesting part of this. It hadn't occurred to me before.

[@julianvalenti]

Yes! Is a very strange face of electronics. That show us thath all is relative to an arbitrary reference poit

[@benthere8051]

I worked for a defense contractor before the Christmas raids on Hanoi. We did evaluations on ECM gear for the B-52s against captured radars. We had to duplicate the specifications of the devices used in the captured radars. I remember we had to work with our distributors to find the worst diode possible to match what we found in the foreign radar. Sounds like the transistors supplied to the American hobbyists came from the same distributor.

[@MIKROWAVE1]

There were many technology hotspots that came out of the post WW2 years and the early radar research. One such place was America's Technology Highway RTE 128 ringing Boston.

[@MirlitronOne]

Hi Mike, it may be worth mentioning that a high hFE value measured in a germanium transistor may be indicative of a high leakage current through the transistor. To check this, disconnect the base and test again. Also, some old germanium circuits actually relied on this leakage to bias the transistor, unlike when using modern silicon devices. I know of at least one radio repair man who extracts the innards of a duff germanium transistor and replaces it with a modern silicon device with a bias resistor attached, then fills the case with epoxy to make the fake look authentic!

[@MIKROWAVE1]

Very cool. A couple of my test subject made the meter go nuts with an impossible value. I suspect that this that effect!

[@VintageTechFan]

@@MIKROWAVE1 Quite a few of them also suffer of tin whiskers. The inside was coated in very pure tin which grew whiskers over time which often make a dead short between all three pins, at least they create intermittent faults. The european AF11x are notorious for this, and since its basically an aging issue, it effects much of the NOS as well.

[@billharris6886]

As a retired RF engineer, I see several parts of this circuit design that may cause unnecessary problems leading to frustration by someone trying to get the circuit working after assembling it. First off, the audio input impedance will be around 600 ohms, which is ideal for use with a dynamic microphone. However, the dynamic microphone output is such a low level, it may not suffiently modulate the oscillator. (2) Modulating the oscillator is this fashion will cause it to simultaneously generate AM and FM modulations. In the receiver, it will likely produce distorted sound as a result, which may be acceptable. (3) Using a single base bias resistor makes the circuit extremely transistor beta and temperature sensitive, meaning the values of resistors R1 and R2 will need to be adjusted depending upon the individual transistor being used. High beta transistors could saturate, whereas low beta could cause partial cutoff. I suggest using a resistor voltage divider at each base plus, an emitter resistor of about 100 ohms. (4) Add a DC blocking cap of 0.1uF between the antenna and circuit to avoid blowing out the circuit if the antenna terminal accidentally touches the microphone ground. (5) The circuit operates the oscillator above the transistor cutoff frequency, which means there is a good chance the oscillator won't start. I recommend a transistor with an Ft of at least 10 MHz. (6) I don't recommend using germanium transistors, they are so old, the junction can turn back into sand without warning, they are poorly spec'ed, more easily damaged by soldering heat, more difficult to source, and more expensive. I recommend instead something universally available, like a 2N2222A (or MPS2222, PN2222, or 2N3904). Sorry to give the impression I am taking all of the fun out of this project. I just remember back when I was a kid assembling circuits like this, and then finding it didn't work because it was poorly thought out. The person that designed it only built one (or a small sample size) without considering the part tolerances and assumed every following one would work just as well.

[@MIKROWAVE1]

A voice in the wilderness that the poor kid would have needed. Foreshadowing.

[@billharris6886]

@@MIKROWAVE1 I can work up some values for my suggestions if there is any interest.

[@PeopleAlreadyDidThis]

Ugh, Poly Paks. I guess I was 13 or 14 when I placed my one order. My poly bag of “assorted” disc capacitors contained about 200 of the same value. Seems remarkable now, but times were tough for us then, my dad just starting a new business. He was not pleased to see $1.98 wasted like that. I was done with Poly Paks. Reminds me of the other ads, though. James Electronics did OK, still going as Jameco. I had a little Sylvania transistor applications book, maybe late 1950s. Lots of single transistor circuits, but most so silly that I never built any. I guess I was afraid to tackle any radio projects, and there was nobody to coach me.

[@subigirlawd_7307]

😍 love this project 😍

[@m0kov]

I envy you for retaining ( or should I say hording ) all those parts, all that test equipment and all that literature. We moved to a smaller house some time ago and I now bitterly regret getting rid of components, magazines and, before eBay inflated prices, vintage test gear. Also, I find it hard to say this, scrapping a wireless set No 22. For some reason I kept all my germanium semi's. Oh the memories, Bi-Pak Ltd and Bi-Pre-Pak Ltd. 73 Steve

[@MIKROWAVE1]

Awesome Steve! All of us are getting to be rare vintage...

[@johnbrewer9833]

Hi. Same here. I worked in a small electronics's research department early 60. One of the reps used to call in with an A5 sized 4 page catalogues. He worked for a little company called Roy S Gibbons and sold basic components and a small selection and some variable condensers and drive cord. This company has now grown into the massive R S Components. I wish l still had the catalogs now but still have a reel of drive cord somewhere.

[@СтаМилАлас]

Bravo 73 milan i Cooking recepti.probaj belu čorbica super jelo. Best

[@MIKROWAVE1]

Moja supruga kuha White Chili. 73 Mike

[@julianvalenti]

Hello Mike! Have you seen the regen that I have built? Thanks to You because is the first one thath I have built. I left a link in the part 4 of the regen series. Now I go for this beautifull toy! Thanks you again and 73's!

[@erichkeyes5578]

I like the gain and beta tester is there video on this unit?

[@MIKROWAVE1]

I have a video on Germanium devices that goes over the whole deal of testing and circuits.

[@erichkeyes5578]

I have just watch Germanium ad Nauseam video Thank You for the IINFO. I will be making some testing boxes up.

[@Lechoslowianin]

I think with a 220K resistor you can adjust the modulation depth

[@MIKROWAVE1]

As you will see - there will be some "adjusting"!

[@DAVIDGREGORYKERR]

what about a long tailed pair configured as an oscillator and the modulation applied to the bottom transistor would that work.

[@hallieboy]

I bought a loopstick from Lafayette for $1.50 when I was a kid That's like $10.00 in today's money. Still, when they pop up on Ebay they go for about $40! Who knew then?

[@MIKROWAVE1]

Sounds like you should go into full production!

[@mtkoslowski]

hFE is the abbreviation of : [ Hybrid parameter Forward current gain, common Emitter ]

[@shaunsiz.itsbetterbytube2858]

Nice to know

[@iceberg789]

one of these days, i need to try to get a ham license.

[@MIKROWAVE1]

YODA SAY

[@milesprower6641]

I believe I have a single Ti 2N104

[@MIKROWAVE1]

Same basic characteristics low Hfe fairly low voltage PNP.

[@DAVIDGREGORYKERR]

You must keep it to a pico watt or the relevant authorities will come down on you like a ton of bricks.

[@andrzejpl9897]

I love your all videos but some of schematics are so bad . This one is good example . Is it not better to have ground on the bottom , supply voltage on top , minimum crossing lines ? Little beet clarity ?

[@MIKROWAVE1]

Well that is because it is the schematic from the book! No clarifications or attempt to make it look "right" has been made. But this will happen when I get to the "modern" version in the next video.