A super-het radio runs 5 years on a C-cell, plus a pentode radio
Ron Quan, analog aficionado and inventor of the dreaded MacroVision VHS content scrambling system, saw my blog about a radio that uses Russian rod tubes. I saw Ron Saturday at the last eFleaof the season and we got to talking about the rod-tube radio. In the course of telling me how much he liked the blog, Ron mentioned that he did a super heterodyne radio that would run for 5 years continually on one C-cell. I asked him to send a picture, which he did yesterday. As a bonus Ron also included a picture of a pentode tube radio he designed. The pentode is cool since it is regenerative, the low-power radio is neat since he used a crystal headphone to save power. Ron notes:
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- On the low powered radio, a crystal earphone was used. I figured driving a 32 ohm headphone drained too much power. Typical transconductance of the IF amplifiers was about 900 micro mhos, but the equivalent tank resonance resistance was about 50 K ohms. This gave about a gain of 30 per IF stage including loading effects of the subsequent stage. The hardest part was taking apart a 10 mm IF coil (without a built-in capacity or) and unwinding it and then rewinding it again for the desired inductance and tapping ratio for the oscillator circuit. Anyway, the whole radio including its audio amplifier, oscillator, mixer, and two IF stages had a total current drain of about 140 micro amps. The sensitivity and selectivity was quite good, able to pull in KFMB (San Diego) to KOMO (Seattle) off the ferrite antenna coil. I figure my next version may drain less than 100 microamps.
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- The regenerative radio was built with a pentode using 27 volts for the plate and screen voltages. Although the filament was meant for 2 volts, the two D cells (3 volts) provided longer running time, which also powered the three transistor audio amplifier for 32 ohm headphones. Unlike most regenerative radios, this one had no external antenna, and the built-in ferrite loopstick antenna coil received KOMO 1000 KHz from Seattle. Also because the regeneration control enhanced the Q of the tank circuit, selectivity was comparable to a superhet. Not bad for just one LC tank circuit.
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Way to go Ron. If you folks like these projects leave a comment and maybe I can convince Ron to dig out or reverse-engineer the schematic. A lot of savvy guys like Ron don’t realize the rest of us need a detailed schematic, even if it is drawn on a napkin, to figure out what is going on. To my Ham buddies like Phil Sittner and Alan Martin, Ron probably gave enough information in the blurbs above to build the darn things.
[Update, Nov 29, 2011] Ron Quan was nice enough to send a schematic and a few comments about the regenerative radio:
- Here is the schematic for the regenerative radio that was designed and built in 2007. I decided on a 1G5 tube, which is normally used for an audio output tube. My initial test showed that this radio, located in Silicon Valley, did quite well receiving KFMB (San Diego), KKOH (Reno, Nevada), and a couple of Sacramento stations. Later on, I picked up KOMO 1000 in Seattle. After getting the tuner section working, I had to decide on the audio amplifier. So I thought of “bridging” the older tube technology with germanium (2N217 and 2N1304) and silicon transistors (2N5089) for providing the audio.
Click to enlarge:
Dick Bauer commented:
Great projects like to see more
Steve T commented:
For a candle heated tube, does it depend on the emissivity of the cathode coating material so it emits more than the plate, which is at the same temperature? If a 100-200C can change the electron generation so much, can you get microamp type currents at room temp, or is it an e^k*T type dependency? Could I focus light, like on a photo tube with a grid inline? It seems I could better concentrate solar or candle energy that way.
Don commented:
There are many of today’s youth that experiment with electronics and other technical disciplines. I doubt the percentage is any different than 50 years ago. Robotics, computers, rocketry, digital signal processing and tube and solid state audio are just a few areas.
A number of hams posted. Most hams did not build any gear….ever. Even fewer built receivers that could be used on the air.
I like Ron’s work. He is among a select group who have built working receivers.
I particularly like seeing his dead bug or ugly construction technique. This tells me these projects are only a tip of the iceberg.
Don K5UOS
Hue commented:
What kind of Russian tube has a cathode you
can heat externally with a candle? I kinda tend
to, uh, like not totally believe this without seeing a specific tube type i can look at.
batavier commented:
mico "mho" wow you are old school. (For all you yousters: "mho" is "ohm" spelled backwards. That unit was replaced by "S" - "Siemens" - as opposed to "s" - "seconds")
bdcst commented:
Well, I still work with fire bottles but mine use at least 9 kV on the plates. Ouch! My first radio was a kit comprised of a 1N34 diode and a CK722 germanium transistor. Worked well for all five of the high power stations in my childhood neighborhood. Fidelity was amazingly good as there were no narrow IF filters to content with.
Hans J Weedon commented:
Hi Guys.
I was surprised to find that no-one picked up that this can not be a super-het (Super Heterodoxy) invented by Colonel Armstrong. This is a regenerative receiver, no IF and mixer.
Any way it is nice to see that some of the tube-life is still there. You can find the tube characteristics on Frank's website tubedata.itchurch.org/index.html
I have designed tube-circuits for over 65 years but my favorites were some tubes made with helper grids, so everything ran on 3V plate and all. Those tubes are very hard to find today.
There is a whole series of European tubes that draw 25mA heater current at 1.4V. They should work fine on 18V on the screens and grids.
Those tubes begin with D and end with 96. Like DAF96 = 1.4V heater Pentode with Diode and 25mA heater.
Hans J Weedon
Radio guy commented:
So where is this "indirect link" to the schematics located?
John P. Guckel commented:
What is really sad is that the kids today don't even know what vacuum tubes are! When I was a kid, living near IBM's facilities in upstate New York, I saw my first computer. It was huge! Racks and racks of modules that were filled with 12AX7 dual diodes. Then I got a tour of the plant and watched them make "Memory Stacks". They consisted of a square frame with read, write and inhibit wires strung through ferrite beads. Those were the days my friend!
Just Me commented:
To all those who are ranting about schematics and not being herd if you look closely there is an indirect link to schematics, etc. So seek and you will find.
arclight commented:
Great work! This is how you introduce youngsters to doing something more than just "buying" technology.
Edwin Pettis commented:
The pentode may be a 34 which has a 2.0 VDC @ 60mA filament and reasonable Gm and mu, other possible tubes are the 1A4 and 1B4. At 27 volts plate, the 34 would probably have a plate current under 100-200 microamps.
pepelux commented:
hi everybody. nice homebrewing!! would be great if we can get the schematics just to try reproduce the same circuits!
thanks a lot in advance,
mathman commented:
Oh boy! I had to use pencil lead and a razor blade; my family could not afford my electronics "hobby". I took old tv sets apart to get components. Ham radio came next. High voltage and rf burns put a temporary stop to that. If ya don't experiment, ya don't invent!
Leonard KS4RN
Darryl Widman, KF6DI commented:
Reminds me of my voltage doubler crystal set I designed as a kid that drove a speaker using an audio output transformer. Had radio playing 24 hours a day for free. Of course, I lived 3 miles away from KMPC, 50kW powerhouse radio station!
Dan DaSilva commented:
I am not impressed. Did you notice that the Energizer Bunny was supplying the power?
Battar commented:
It seems that the US of A is the only place where multi-KW power AM stations still exist. (BBC world service excluded). Does anyone remember the ZN414 AM radio-on-a-chip, in a metal TO-18 package?
Mad Hatter commented:
I love this stuff! This is the kind of stuff that got me started in the field.... way back when.
John D. commented:
Fourteen states with one watt to a 6AU6 on 40-meters?? I guess I went the QRO route, what with seven watts to a 6AQ5. The furthest I ever got with that was from Rego Park to the other side of Forest Hills, Queens.
LeeM commented:
As a kid I never was able to get the razor blade radio to work (and I -was- using the "blued" blades) but I did once turn a broken vaccum cleaner into a radio:
I was using a D-cell battery and a pair of headphones as continuity checker, I did not own a multimeter :-(.
When I was checking the motor I heard 2 local stations (no selectvity), as I turned the motor by hand the sound cames and went as the brush and corroded commutator bar lined up.
jimbo44mag commented:
These look like great homebrew projects. A schematic and a suggested parts list would be helpful to have. My kids have shown a little interest in radio, so building a few of these might fuel their further interest in science..?
Naresh commented:
Great idea ,I have made radio without any power just conecting one OA79 diode between to terminals of head-phone
Herm commented:
I remember the cat whisker radios well.
As a Ham I played around with low power alittle. I worked 14 states with a 6AU6 one-tube transmitter running 1 watt on 40 meters CW.
Those were fun days back in the early 1950's.
Dr.LAL commented:
Ah brought back memories of Fox hole radio ...the Germanium diodes and the cat whiskers...great article !
AE7DG commented:
I like the idea of heating the cathode with a candle. Classic. Or we could use a convex mirror and solar energy to loosen-up the electrons with some heat. That would be a nice ironic twist to combining a vacuum tube with solar energy.
John commented:
Great seeing usable radio designs using parts large enough to see without a microscope. I learned electronics using tubes, built a Heathkit analog computer in 1964, it used op-amps built with 2 12AX7s as a differential amplifier, first time I used negative feedback. During WWII knowing how to build a radio receiver using a razor blade, wire, crystal headphones and oatmeal box for the coil meant being in caontact with the rest of the world, the BBC at that time.
Radioroom commented:
An old octal pentode with a 2v filament? I have loads of antique types but can't place this one without an old manual in front of me. Very innovative - maybe he's doing penance for the Macrovision work;). Very nice designs. Also, a planned superhet with a draw of under 100ua?? Gotta see that. Feeling the need to build again.
seacrow commented:
Great... setting the EE field back 80 years. How about going back further and using a catwhisker on a lump of galena? Sheesh... and no schematic to boot. Like Weird Al's DEVO parody: "Dare To Be Stupid!"
itctrans commented:
Hello
how about including schematics?
Tx
itctrans
Curt Carpenter commented:
These look to be in the very finest tradition of the art! Well done.
KA4IWG commented:
VERY nice! More projects and schematics would be appreciated. Regen radios have had a rebirth in recent years.
Paul commented:
Well if you used a Russian pentode, you don't need "C" cells to run the filament. Could have used a candle under the tube heat plate. This was a common practice in Russia years ago when batteries was a luxury and ran on candle heat. That would have gotten you another year and cost a box of candles.
Ken commented:
These look like fun projects, how about including schematics?
Widar commented:
These projects are great. I would like to see more of them.
