Tube TX

is there any other advantage to building an AM tube TX

Well...it might help supplement heat along side the open fire boiling water in a kettle with a cap and pressure valve steaming a small engine turbo turbine turning a generator powering it. Lots of neat things can be done with a tube TX. 🙂

They would be capable of surviving a destructive EMP bomb attack.

They could survive a deadly severe solar flare.

They make great conversation pieces at 4 o-clock tea time.

They can take a drastic mis-match on the output and make the plate glow and still throw a signal. (2nd best party ice-breaker)

And if equipped with the non-polarized AC plug...they make a great equivalent to a bug zapper for people. (1st best party ice breaker)

Ya...lots of neat things can come about with a tube transmitter, especially when showing it to a plumber and explaining you just built a new valve device! 😉

RFB

This tube circuit looks very much like the Knight Kit circuits we've talked about.

Tubes at part15 power don't interest me, but when there is a tube buffer amp and a tube final with a big knobbed variac and 700VDC B+ and a row of meters, the fun begins.

"Lots of neat things can be done with a tube TX. :)"

Yuhh, I know. 'Course I meant as far as things like audio signal 'warmth' without a plethora of outboard stuff. I have a friend with lots of vinyl records and magnetic tapes ... I was thinking I could get a tube amp and tube compressor/limiter and set aside an hour for strictly local analog broadcasting, no internet.

I would do it late night, with the transmitter and other tube units set glowing in the studio window, some light on the analog mixer and TT, and the rest all dark.

Also, you may have forgotten one thing ... and it probably wouldn't work with this low power, but maybe I could cook hot dogs?

ken N. you have brought the memories back and I think I'll get sad.

I loved and worshiped tubes when I got started, and built many circuits, and loved the sound that tubes could bring.

I had two amps, an Eico 50-watter which absolutely sounded fabulous and loved balancing the output tubes with meters so neither side was over driven. And there was the Heathkit 30-watter, every bit as good, Eico preamps for the turntables with the fun of trying different loading resistors to match the cartridges (50k ohms was the standard).

Foolishly I felt the pressure of fashion to go solid state, but in reality I don't think my clients knew one way or the other.

I think the tube designs for 100 mW
input Part 15 transmitters are wonderful.

There are a lot of different versions out
there.

Long ago, there was a design that used a
6V6 final amp, running only about 20 volts
on the plate, as I recall. It was driven by
another tube. This circuit really put out
a big kick, but I have not been able to
find it. Apparently, the 6V6 was very
efficient running at that low plate voltage.

The drawbacks, of course, for most of these
designs, is the high voltage. And most of
the transmitter oscillators used LC circuits
and they drift. Then if you wanted to take
one of these units out in the back yard,
that would be tricky.

Still, I love glowing tubes, and I wish I
could build one of these designs just to
have it. And use it in the house.

Best Wishes,
Bruce, MICRO1690/1700

"The drawbacks, of course, for most of these designs, is the high voltage. And most of the transmitter oscillators used LC circuits and they drift."

So what about the crystal driven circuit project I posted? Wouldn't that take care of drift?

Yes, my friend, you are absolutely right.

In fact, that is a really good circuit.

What I meant was that most of the
circuits I have seen out there (in my
experience anyway) use LC in the
oscillators. The two phono osillators
I had drifted. If I was to build something,
it would probably be the one you posted.

Best Wishes,
Bruce, MICRO1690/1700

Crystals are not the only means to prevent drift. You can use the existing LC circuitry in the thing and simply add a varactor diode with its tuning voltage controlled by a PLL loop, and not only do you get stable frequency, but a variable stable frequency rig to boot.

PLL kits are cheap, around 30 bucks and varactor diodes are also incredibly cheap.

RFB

You could add warmth and glow to a solid state transmitter with some power resistors and LEDs. In fact somewhere on the web, there's an audio preamp available that harkens back to the good old days with a visible phony tube that glows and gets warm.

Somewhere on the web, someone said that if you built a cell phone with tubes, it would be the size of the Empire State Building. That was a few years ago. How big would it be now that cell phones are equivalent to personal computers.

PhilB, you remind me of the early days in starting my recording studio. I guess I must have been thinking "movie prop," but I actually believed that I could make my studio appear more important by having two extra racks loaded with fake electronic activity including meters, lights, variacs, switches and whatever looked "serious." I never actually built it, but it seemed like a good idea at the time.

Don't forget the pannel with the large red button and words "Self Destruct"....even Flash Gorden's famous rocket had that!

RFB

This world seems to be self destructing without a button.

But the button creates the illusion that it's up to us.

But did Flash Gorden's button destroy the rocket or him?

Of course, there were many Flash Gordons, perhaps the strangest being the eps filmed in Germany.

http://www.archive.org/details/TheAdventuresOfFlashGordon

I think the self destruct buttons destroyed whichever the plot called for 🙂

I'd like to see a schematic for this puppy:
http://www.ontheair3.com/index3.html

Emission type: A3 Amplitude Modulation.
Modulation Type: Cathode Modulation.
Modulation Capability: 125% Positive Peaks, 100% Negative Peaks.
Carrier Shift: less than 0.8%
Frequency Range: 530 kHz to 1705 kHz
Frequency Response: 25Hz to 22kHz
Audio Input Level: less than 500mV
Audio Input Impedance: 4 to 32 ohms.
Distortion: 0.75%
Frequency Stability: 0.005%
Tube Compliment: (1) 12SA7 Oscillator, (1) 12W6 100 milliwatt PA

That would be sweet....