Comments on: Homemade regenerative tube radio

By: luke

luke — Sun, 26 Jul 2009 11:22:18 +0000

Ahah! Valves!

By: Richard

Richard — Wed, 15 Jul 2009 17:18:05 +0000

@ac7zl
yes I have – although it was a considerable number of years ago (end of the 60s) so it may have been before they started with the gas-filled bulbs… I always got the best results with the ‘Lucas’ brand bulbs that were very common then – i’m no longer able to drive so I have no idea if the brand even still exists.

By: localroger

localroger — Wed, 15 Jul 2009 12:47:19 +0000

lekernal, the whole basis of using a triode as a radio detector is that during the half of the RF waveform when it’s positive you are not blocking the flow of current to the plate, and during the half when it’s negative you are. The half when it’s positive is normal and does not damage the tube as the power flowing during the positive cycle is trivial — that’s why you want to amplify it.

By: lekernel

lekernel — Tue, 14 Jul 2009 21:06:49 +0000

no, you really should not run a tube with a positive voltage on the grid (which, contrary to a negative voltage, will generate a significant grid current) – it is very fragile and dissipating any power into it is likely to shorten the tube life.

By: Steve Watkins

Steve Watkins — Tue, 14 Jul 2009 18:32:31 +0000

lekernel.

seems to me that you are refering to grid biasing which is well beyond the scope of a crash course.

By: ac7zl

ac7zl — Tue, 14 Jul 2009 18:29:35 +0000

@richard-

Have you actually *tried* this? It seems as though it should work in theory, but in reality it does not.

I don’t believe that tail lamp bulbs are evacuated, but might actually be pressurized with something inert (perhaps argon) in order to improve the life of the filaments.

One time, I heated the glass on one of these bulbs with a torch until the glass softened. Instead of collapsing inward, as I would expect if the envelope contained a vacuum, it actually bubbled outward. When the bubble burst, gas could be heard to escape.

I have tried numerous tail lamp bulbs and have yet to observe any diode action.

If you carefully punctured the glass envelope, and evacuated the interior, then, yes, you would surely see some evidence of diode action.

@richard said:
>At a pinch, a car stop & tail bulb with two
>filaments can be pressed into service any time
>you need a diode… heat one filament, and stick
>some potential on the other one, and you’ve got
>one-way electron-flow. :-)
PS: Forgot to say good post!

By: ac7zl

ac7zl — Tue, 14 Jul 2009 17:46:15 +0000

@richard-

Have you actually *tried* this? It seems as though it should work in theory, but in reality it does not.

I don’t believe that tail lamp bulbs are evacuated, but might actually be pressurized with something inert (perhaps argon) in order to improve the life of the filaments.

I have tried numerous tail lamp bulbs and have yet to observe any diode action.

If you carefully punctured the glass envelope, and evacuated the interior, then, yes, you would surely see some evidence of diode action.

By: markps2

markps2 — Tue, 14 Jul 2009 14:07:57 +0000

Nice old school electronics.

By: lekernel

lekernel — Tue, 14 Jul 2009 13:56:42 +0000

oh, and digital design can be an art, too. see this for example: http://cva.stanford.edu/publications/2002/imagine-overview-iccd/
or some advanced gpu… fpga’s make development with these design techniques available for a few bucks nowadays.

By: MrX

MrX — Tue, 14 Jul 2009 13:56:14 +0000

@tom mac
That battery doesn’t seem very portable, was it?

By: lekernel

lekernel — Tue, 14 Jul 2009 13:54:23 +0000

It’s not hacking.

By: MrX

MrX — Tue, 14 Jul 2009 13:48:35 +0000

WTF is wrong with the arduino?

By: Agent420

Agent420 — Tue, 14 Jul 2009 13:42:48 +0000

“@stunmonkey: Correction. People were able to build things before they had the difficult task of *thinking* taken out of the equation. ”

while i agree to some degree, i think another element here is the fact it is a pure analog project – we don’t see too many of those these days other than some kind of headamp clone.

good analog design has always been more of an art than digital imo, and i wonder if we may be losing some of that in our modern digital age.

By: localroger

localroger — Tue, 14 Jul 2009 13:26:42 +0000

I did something similar a couple of years ago from a Boy’s Life article published in the 1930′s. My variable cap was two pieces of aluminum foil glued to pieces of wood sliding past one another with a piece of cellophane in between. The tube was a type 30, and I think that’s the same one used in this hack; it was one of the earliest low power filament types. If you use two batteries for filament you need to put a silicon diode in series to drop the voltage a bit, because it’s designed for 2V and 3V will eventually burn it out. Not good for a tube that’s survived 80 years before you put it in your hack. I used 3 9V batteries in series for B+.

By: lekernel

lekernel — Tue, 14 Jul 2009 12:36:03 +0000

contrary to what the article says, the grid usually has a negative potential, which repels electrons and cuts off the plate current (the more negative the grid potential is, the more electrons are repelled, the smaller the plate current)

quite a shame to see technical errors as soon as hackaday goes a little bit further than arduino so-called-”hacks”.