There have been a few mentions of valves in recent threads, and prompted by this I have taken the first small step towards a valve activation.
Consulting Mr Google, I found a design for a “cigar box transmitter” published in Short Wave Magazine in 1955. This uses 1.5v heater valves intended for portable radios, and I found all the bits in my junk box (or shack, as I like to call it). Output is given as 1 Watt. http://sm0vpo.altervista.org/tx/cigartx.htm
I’ve just lashed up the oscillator stage using a DL94 valve and a 7.025 MHZ FT243 crystal. It oscillates, and, to my surprise, there is minimal chirp when keyed.
The output stage uses a tapped anode coil, designed to match a half wave end fed wire - I may use a Pi tank arrangement instead.
I’m using 10 x 9V PP3 batteries to provide the 90V HT. This will be an expensive choice if I use this thing regularly, but in that case I’ll consider an inverter. To get started, it was the quickest and simplest solution and is in keeping with these valves, of course.
So, a way to go yet, but I thought I’d post now to get the ball rolling :o)
There is too much uncertainty to suggest a date for activity, so I suggest aiming to get on the air during 2021.
Please post in this thread, and of course, Alert for any activations.
Glow bugs, Para Sets, whatever, lets see and hear them!
Interestingly, it has a centre tapped heater. I’m using them in series with 3V at 50mA. You can also use them in parallel at 1.5V 100mA. Or, you can just use half of it 1.5V 50mA in economy mode, and derate the anode current accordingly!
One of the first books I read on radio when I was 10 featured a TRF design using D-series valves. You could build the radio in stages with each subsequent chapter using the radio built so far. The final chapter used a DL94 for the audio stage. I’m shocked but my memory is weak on the transistor design in the last chapters though I do remember it used OC45 and OC71s. Must have been published in the late 50s/early 60s.
There was a large chunk on batteries and their suggestion was it was always a better idea to use separate LT and HT batteries rather than combined batteries, 90V for B+ and 1.5V for the heater. The idea being the heater often ran down before the B+ and with separate batteries you did waste the unused section.
I started playing with valves as a way to relax from professional cognitive digital software radio design. To me, it’s a pleasant creative mind boost. The radio part of the transceiver contains a unique detector, which I have never seen published anywhere. I named it after its principle of functioning the synchro-regen.
Back around 1957/8 I got a one valve regenerative kit for LW/MW which used a 1T4 valve, this tuned down to Top Band and I heard my first hams with it. It also got me interested in short waves and I built another version with plug in coils. After seeing an AF amp circuit in “Camm’s Comic” (Practical Wireless) I added an AF amp using (IIRC) a 1S4, and later an RF stage using another 1T4. This was surprisingly sensitive and with careful setting of the regeneration control I could resolve SSB, though I had to tinker with it to cure hand capacity effects making SSB tuning a feat! When I started studying for the exam I got as far as drawing a circuit for a compact low power AM
transmitter using the same valve series but never built it, moving instead to UHF!
As a possible alternative, I have seen NiCd PP3 batteries in Poundland, I have’nt been in one since the Autumn but I would guess that they are still available. Cheap and cheerful, though it would probably be a pain dismantling it to charge them individually!
I’m working on a tube superheterodyne rx. The goal is a portable cw rx and later tx for 80/40 m.
For this reason I used a tube set that works with 12V! Anode voltage. ECH83, EBF83, EF98, 12K5.
Yesterday I was able to check the broadcast 31m band for the first time.
I recent build a 1W xo tube tx for my rx. Today I try to do my very first dx qso with Lars, SA4BLM (tnx Lars) and it works fine.
The rx is running, but I doesn’t loose his signs.
In the video, you can’t hear my sidetone but the mechanical clicks of my fine BamaTech key and the rx/tx relais.
After the qso, Lars told me, that I was on the side of his beam, hi.