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crystal radio using vacuum tube diode
Posted: Fri Jun 01, 2007 11:01 am
Hello Forum Members:
I would like to build a simple crystal radio receiver (coil,diode and antenna) using a vaccum tube diode instead of a germanium diode. This would be my first vacuum tube project and seems to be about the simplest practical application. If I can get this simple application to work, maybe I can move on to more complicated projects with vacuum tubes.
Is there a simple, cheap vaccum tube and socket available for something like this?
If so, what are the part numbers and where can I get them?
Posted: Fri Jun 01, 2007 11:28 am
Well, that would not be a crystal radio. If that is what you want.
The circuitry just to put a vacuum tube to operate with its voltages, transformer, rectification, etc... is much more than the 'crystal' radio circuit itself that you may be looking for.
Posted: Fri Jun 01, 2007 1:23 pm
Thank you for replying.
Actually, I'm not necessarily looking to build a "crystal" radio. What I want to build is a simple vacuum tube project.
If I do build the receiver, the vacuum tube would simply replace the germanium diode in the detctor circuit. It should work??
There would be transformers, and volatges and rectification and all that stuff, therefore I would also need help with a circuit design.
What I am after is: I would like to build a simple vacuum tube project. I know there are tons of guitar amp circuits and audio amps and all that stuff, but I'd rather start with the simplest application possible.
Posted: Fri Jun 01, 2007 1:30 pm
The 6AL5 was a dual diode that was sometimes used as a detector. The heater would require a 6.3 VAC transformer with a curent rating of .3 amp or more. This can probably be obtained from Radio Shack or a surplus store. The tube and miniature 7 pin socket can be obtained from Antique Electronic Supply (www.tubesandmore.com
). Surplus stores may have the parts at lower price, but at considerably more effort in locating them.
An older version of the 6AL5 is the 6H6. This uses an octal socket and is much larger. It also may be less sensitive.
Posted: Fri Jun 01, 2007 2:38 pm
Learning how to use tubes is fine, ......but,.....The tube diode is like replacing a Volkswagen with a Rube Goldberg contraption.
Anything but simple by comparison.
Superior yes, but complex compared to simple.
Posted: Fri Jun 01, 2007 2:56 pm
Just a note to RS's reply. You probably will not find a better diode than the 6AL5 as there is no offset voltage and starts conducting at anything above 0 volts. (as is the case with any lo pwer vaccum tube rectifiers) Seems like the radio would be more sensitive than using a semiconductor.
Posted: Fri Jun 01, 2007 3:19 pm
My bad for using the word simple. I looked up some info on the 6AL5 vacuum tube diode and now realize how complicted vaccum tubes and their applications really are. The diode application on a receiver seemed like the simplest way to actually use a vacuum tube until I just did the research. I may end up trying to build a 6AL5 Tester instead (some way to bring the tube to life).
Thank you for the information on the 6AL5 and socket. This looks like a great vaccum tube! I found some data sheets and hopefully with some more thinking can come up with a suitable application. Either way I will purchase these and put some voltage on it, see what happens.
Thank you for replying. Any ideas where I might find a circuit design for an application? Again, I am looking for the simplest circuit I can find.
Posted: Fri Jun 01, 2007 4:54 pm
For a diode receiver, you only need a heater supply for the 6AL5. This can be supplied with a transformer with a 6.3 volt secondary winding.
Only one section of the 6AL5 is needed for a simple diode receiver. It can be used to replace the crystal diode in any design for a crystal set with no other circuit changes.
Posted: Fri Jun 01, 2007 5:54 pm
I think it is possible to do the circuit with out a 6.3V transformer. I remember doing something similar a long time a go. What I did was put a regular 120V lamp bulb in series with the vacuum tube filament. It took a long time for the tube to light but it worked. I just did the math and 36 watt bulb would be ideal. I am not sure of all the sizes of 120 bulbs but a 40 watt just might work. Because the filament doesn't need to be common to the rest of the circuit the danger area is minimal.
Posted: Fri Jun 01, 2007 8:14 pm
The whole point of using a vacuum tube would be that it can be an amplifier. Using one just as a diode makes no sense.
With plate/cathode/grid tubes, you need high voltage for the plate. This can get dangerous.
Posted: Fri Jun 01, 2007 9:40 pm
If memory serves me right, the 6AL5 filament requires 150 ma. A simple task for the right wallwart (6V @ .15 A), The filament voltage dosn't have to be to precise - +/- 10% will do fine. These tubes were used in millions of receivers as AM detectors and FM Foster-Seely discriminators (FM detector). I am not sure what your end goal is, but there are old tube books for sale on E-Bay, which would give you a lot of circuits and info. Also a Google search will locate info under Antique Radio or Vaccumm tubes. Many threads from there also.
Posted: Sat Jun 02, 2007 6:20 am
Robert Reed wrote:If memory serves me right, the 6AL5 filament requires 150 ma. A simple task for the right wallwart (6V @ .15 A), The filament voltage dosn't have to be to precise - +/- 10% will do fine. These tubes were used in millions of receivers as AM detectors and FM Foster-Seely discriminators (FM detector). I am not sure what your end goal is, but there are old tube books for sale on E-Bay, which would give you a lot of circuits and info. Also a Google search will locate info under Antique Radio or Vaccumm tubes. Many threads from there also.
My RCA receiving tube manual confims that the 6AL5 require 6.3V and 0.3 A. A wall wart is a reasonable way to get the filament voltage.
Posted: Sat Jun 02, 2007 10:20 am
I guess memory didn't serve
. Its 150 ma per filament and being a dual filament would make it 300 ma total as you pointed out.