I like watching tv programs about electronic pioneers like Marconi, Edison, and Tesla. I marvel at what they could accomplish without the technology like we have today. Now the use of tube/valves has declined since the invention of the transistor. Today we have opamps and discrete FETs for VLF and LF gear. Design software is for semiconductors, not tubes. I don't understand why anyone would promote vacuum tubes .
Regeneration for receivers was an awful wild idea, it's like saying the howl (microphony) of an older design Public Address system is useful.
Not promoting the use of tubes (valves) just wish to preserve knowledge of that technology. Tubes have safety problems associated with the need for high voltage power supplies. That said electron tubes have very low capacitance and when correctly designed they could be used at very high frequency stretching as far as 4GHz.
It's not true that design software is (only) for semiconductors. Several schematic programs include symbols for valves and there are Spice models for many valves so they can be used as components in simulation programs. You can find much written about valves and even Spice models on this DiyAudio site.
Tubes in many ways are analogous to JFET's
The SAQ receiver design will work for 60kHz.
Just wind about 300 turns for the Ferrite Rod and alter the value of the 4n1 COG capacitor making it smaller so that the circuit resonates at 60 kHz, something like a 1n5 capacitor should be close. You will need a scope or something that can digitise at 192 k samples per second to see the signal.
Make the 100p U1A feedback capacitor 47p and swop the LM358 for a faster dual OpAmp.
@fubar3
Here is an updated version of the SAQ receiver design intended for 60kHz. As mentioned the number of turns of wire wound on the Ferrite Rod would need to be adjusted to get resonance at 60kHz.
This is a starting point. I'm sure that this design can be improved upon and will most likely need more bandpass filtering. Without antenna and earth connection the ferrite will be directional.
Here is an updated version of the SAQ receiver design intended for 60kHz. As mentioned the number of turns of wire wound on the Ferrite Rod would need to be adjusted to get resonance at 60kHz.
This is a starting point. I'm sure that this design can be improved upon and will most likely need more bandpass filtering. Without antenna and earth connection the ferrite will be directional.
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We all do sometime or other! Yes interesting design! The first triode has very similar configuration to SAQ Valve Receiver above.
That said, and after some more evaluation, I think there are far too many capacitors and their values don't make much sense, the front end of that circuit between the antenna socket and V1a is especially weird. I'm not a fan of dual valves either, they were developed because of commercial pressures during the valve TV set era.
My antenna is a (somewhat, but enough) circular loop, 7 m circumference, IOW large. It's single turn and feeds a low noise, 3 ohm input impedance push pull amp, gain ~40 dB. I'm setting up an experiment with a ferrite rod. It already has a primary of 840 mH, parallel C of 456p and needs a 300 uH turn for NFB.
Is the plane of the loop horizontal or vertical? How many turns in the loop. There is a post where someone had used several turns of Cat5 network cable then wired the ends so that each turn of Cat5 was 16 turns!
My loop is single turn and polarization is vertical. Theory and practice has been described with a wealth of articles at https://lz1aq.signacor.com
I did some homework to arrive at a larger than usual loop, and also developed a very low noise amp for the antenna. So according to theory it would be good for FM too. Only, I had forgotten to measure the field strength of new local FM stations. So they appeared at -15 dBm at the RX which was a bit too high, and some -110 to -130 dB spurs appeared at HF. Hence I had to insert a LPF to attenuate FM.
I did some homework to arrive at a larger than usual loop, and also developed a very low noise amp for the antenna. So according to theory it would be good for FM too. Only, I had forgotten to measure the field strength of new local FM stations. So they appeared at -15 dBm at the RX which was a bit too high, and some -110 to -130 dB spurs appeared at HF. Hence I had to insert a LPF to attenuate FM.
I took another look at this 2003 project. The designers admit they are using obsolete technology but they believe it is still useful. The schematic and circuit assembly look messy at first but it is a sensible project and looks good when finished. The gain is lower than an equivalent opamp circuit but they claim low noise. And it is portable with a 12v battery.
I used to repair tube gear for communication and navigation. Tubes were eventually replaced with solid state. I became a software nerd to continue making a living.
I suppose there will always be niche for tubes because DIY people are motivated by nostalgia and novelty. Then there are the audiophiles. Instead of tubes I would recommend using proven technology for builds .. but DIY hobbyists can build what they like.
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I've seen multi-turn loop antennas inside hula-hoops and bicycle wheels. Yours must the be biggest in the land.
I don't expect to see VLF at my location but perhaps LF. Aside, I used to receive UHF stations from around lake ontario with a homemade fractal antenna but now there are too high-rises blocking my view.
The principle of wideband loop antennas is based on a "lowest possible" Z(in) of the amplifier, and lowest possible inductance of the loop at maximum area. For low impedance devices (common base etc.) that makes single turn loops mandatory for best results. But I figured out that for high impedance devices, feedback can be applied to achieve wideband performance while maintaining the noise performance of a tuned multiturn loop (at optimum Z achieved by NFB). It has been build and indeed, the 10 turn loop on MW (~500 uH) performs well, just as suggested by the sim. Hence my effort to apply that on the VLF ferrite antenna.
That's interesting! Did you ever come across a number 19 set left over from WWII?
Yes tubes obsolete, but ceramic and metal tubes still used examples would be large high power water cooled transmitter tubes and of course the Magnetron in microwave ovens.
I don't think so because with a HT of 200 volt the maximum current that can flow through the 68K Anode resistor is 200/68000 which is 2.94mA. Any OpAmp won't be worried about 2.94mA pulling pin 6 up. However if the Triode suddenly started conducting a heavy current the 22n capacitor could pull a current out of pin 6 but again I don't think the Triode can pull much current (especially before it has warmed up). Also the 300K Grid resistor cannot push much current into the Grid to make it positive of the Cathode (needed to make the Triode conduct a "heavy" current). Something I would test if I built the circuit.
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