In a stroke of luck, I just obtained a couple of 1700KHz crystals. They are CR-18/U, so there is no possibility to open one of them up and grind it to 1700.5 for a two-crystal design, but never mind for the moment.
The avalanche of advice here has been most gratifying. I have tentatively decided to start small and build something like the "Simplex Super Mark II" from the 1963 ARRL Handbook. It's a 3-tube design with a single-crystal 1700KHz filter. There are no unobtainium parts and I already have a stock of the specified Illumitronic/Miniductor coil stock (and even if I hadn't, there is enough info in the book to reproduce them).
The Simplex uses a 6U8A Mixer/oscillator, another 6U8A detector/BFO and a 6CG7 audio stage. "Selectivity at the IF is obtained through the use of a single crystal. This, in conjunction with some regeneration provided by the detector, is sharp enough to provide a fair degree of single-signal CW reception." Faint praise, but it's only a three-tuber.
Three tubes, but with 6 tube circuitry.
A couple of suggestions if you go that route:
1) The receiver provides reception of WWV at 5 MHz, which was fine for US hams but not worth the parts in your application - plus you already have a receiver for 5 MHz. I suggest removing the 200 pF capacitor in the oscillator and S2A, and replacing S2B with an SPST switch to turn the BFO on and off.
2) The power supply uses solid-state (selenium!) rectifiers in a voltage doubler circuit because, when the receiver was designed, that was the least expensive way to get the needed ~250 volts at about 25 mA for the B+. You can substitute other power supply circuits, depending on available parts.
3) I would make the power supply capable of 50 mA or so. The reason for this is so you can add voltage regulation of the tunable oscillator and BFO in the future if you so desire.
4) The stand-by switch reduces the receiver gain by shorting the antenna input and removing the screen voltage from the 6U8 pentode section. For convenience in TR control, I'd make provision to do this with a small relay rather than a switch - that way, you can have single-switch TR control.
I agree with those who have said above that adding more tubes is not that big a deal. But I would prefer to start small and try to understand in depth how it all works on a component by component basis.
That's a good approach. Which leads to another suggestion:
5) Try to use expensive/hard to find parts in a way that makes them easily reusable. For example, I don't cut the leads on power supply and audio transformers or chokes. Instead the extra length is coiled or folded up. I don't pull plates from tuning capacitors.
The result is that parts from a project can be reused in the future.
I have no formal EE training but a love of learning and experimentation.
It should be remembered that electrical engineering is a very diverse field and that Radio is only one small part. Hollow-state radio is an even smaller part.
(Full disclosure: I received my BSEE in 1976. In the four year course at the U, vacuum tubes weren't studied at all.)
Yes I know the performance will be extremely limited but that in itself will be interesting when comparing with the two other receivers I have built already in the past few years, both of them regenerative designs, one of them solid-state (3-transistor ARRL design) and the other one hollow-state (my own design with considerable help from folks here such as G3RZP).
Exactly!
When the building gets under way I will document the project in a thread here, hopefully in the next few months if I can figure out how to set up a small workshop in my current small QTH. (It's a challenge, to put it mildly.)
There was a period, right after University, when I was living in a small apartment. I built a complete CW receiver on the kitchen table, because it was the only suitable table in the place.
I had a toolbox with all the radio tools in it and another box with all the radio parts and the receiver chassis. Before each construction session, I'd cover the kitchen table with old newspapers, take out just the parts and tools needed, and proceed. At the end, the tools went back in the toolbox, the parts went back in the parts box, and the newspapers were wrapped up and put in the trash. Usually the kitchen floor got swept too.
It took some time to build the receiver but it worked well. I should restore it....
Once the Simplex is up and running it will be a pleasure to move on to more sophisticated projects.
Exactly. And the results may surprise you.
73 de Jim, N2EY