[Des] sent in this really cool writeup on building a Regenerative receiver using VFDs. Regenerative receivers are basically short wave radio receivers that use positive feedback to more finely tune the signal. Though they can be built with modern components, [Des] wanted to try to make something that not only looked like it was made in the 30’s, but actually used the same technology. He utilized some VFDs in various places where vacuum tubes were needed. After building, [Des] found that the unit performed very well, better than his authentic 30’s radio that he compared it with. Those VFD’s seem to be everywhere recently. We did the story on using them as amplifiers, and and building display drivers for them too.
Actually, the purpose of regeneration is not to provide finer tuning. What it actually does is provide more amplification. This allows weaker signals to be tuned with the same number of tubes compared to a direct-conversion receiver, which has to provide all its gain in its audio stages. If adjusted so that it oscillates, the regenerative detector also acts as a BFO, allowing you to receive single sideband and Morse code.
Regenerative receivers were THE hot item for long-distance reception before the superheterodyne was invented. (Superhets offer much better selectivity.)
I never would have thought to build one using VFDs as triodes. That’s really cool.
I should add that regenerative receivers often *did* have better selectivity than the TRF receivers that preceded them, but that’s not directly because of regeneration; rather, it’s because the added gain created by regeneration allowed the use of more tightly tuned input filters, which otherwise would have resulted in too much signal loss.
This is incredible. The audio clarity is wonderful. I’ve built some small radios of my own, but never had such great sound. Excellent work!
Vacuum… Fluorescent… Display?
That’s a lovely little hack… I suggested it should be possible in the comments to the VFD amplifier a short while ago, but didn’t dare hope I’d get to see it done so soon.
I’ve just pointed a few of my fellow radio amateurs in the UK to the page to see who fancies a go. :-)
@orv: regeneration does indeed increase selectivity, because the effectiveness of the regeneration is itself affected by the tuned circuit’s willingness to pass the signal. a slightly off-center signal effectively has the regeneration knob turned down compared to one that’s on-center so it’s amplified less, sharpening the selectivity compared to a non-regenerative amplifier using the same LC. This is easily observed when you are operating a receiver like this.
the build details are quite fascinating. he uses tin can lids and “dead bug” construction (minus the bugs, since he isn’t using ICs) to provide a ground plane.
here’s a thought. if the individual segments are separate I wonder if they could be used as a very simple analogue logic/memory element? might be an amusing experiment as some of the first computers were based on op-amps.
-A
Hi there,
Just a few lines to say “thanks” for the feedback and positive comment relating to the “Triodes in disguise” article.
Also, sorry for the “typo” which appears both in the title and in the text. The title reads “Voltage Fluorescent Device” when in fact it should read “Vacuum Fluorescent Device”.
Best wishes to all and thanks to “Hack-a-day” for hosting the article.
73,s
Des. (M0AYF and author of “Triodes in disguise”)
DEs M0AYF de peter KH6CTQ Since I have copied ur artical and read it many times, I have collected many multi -segmented VFD displays and can’t seem to find any single segmented VFD units. Worst case, where a=can I find pinout informaiton. The specific VFd unit in hand is a Futaba 5-LT-91Z or 5-LT-92Z.. Hope you can be of some help.
Tnx es 73s Peter
Hi Peter,
Many thanks for your interest in the VFD project.
Sadly I dont have any pin-out information on VFD’s and was never able to find any. I found the best way to identify connections was to “reverse engineer” the VFD’s. A good description of how this can be done is given on AC7ZL’s page…
http://www.hpfriedrichs.com/radioroom/vfd/rr-vfd.htm
His VFD project is an audio amplifier but the information and tips on working out the pin connections of a VFD’s are still valid for a radio project. The method I prefer is “inspection” with a magnifier to identify the fillament, grid and anode connections.
If all else fails you could try contacting Futaba directly via the webpage…
http://www.futaba.co.jp/en/display/vfd/
I hope this helps and good luck with the project.
72,s
Des (M0AYF)