Forums :: Resources :: Features :: Photo Gallery :: Vintage Radio Shows :: Archives :: Books
Support This Site: Contributors :: Advertise


It is currently Oct Tue 21, 2014 8:03 am


All times are UTC [ DST ]



Post New Topic Post Reply  [ 20 posts ] 
Author Message
 Post subject: grid leak radio
PostPosted: Aug Mon 15, 2011 9:25 pm 
Member

Joined: Dec Sun 23, 2007 8:12 pm
Posts: 56
I trying to build an old style one tube breadboard radio. The problem is, I can't get it to work. What I have is, one tube 39/44, 37, 56, 235,or a 76, the reason I am using one of these tubes is that I have a nice looking 5 pin tube socket. I have used a 100pf 200pf 500pf cap. and a 1m 2m 3m resister. My tuning circuit is an Atwater kent vairable cap and a home wound coil, this works quite fine as a crystal radio, so that much is good. I have connected the tank circuit through a diode and then to the grid to a tube and that amplifys the signal just fine but I would like a grid leak detector. I am using 45 to 50 volts plate voltage when connected as a grid leak.
I'm not using any regeneration at this time, just trying to get it to work as a detector at this point. I would like to find a schematic for a grid leak circuit that uses a 235 tetrode tube becouse I have a nice globe tube and that tube has the grid cap on top.
Any thought as to what I am doing wrong?


Top
 Profile  
 
 Post subject: Re: grid leak radio
PostPosted: Aug Mon 15, 2011 10:36 pm 
Member

Joined: May Tue 30, 2006 4:46 pm
Posts: 6217
Location: Santa Rosa, CA
What are you using for an antenna? This type of detector isn't very sensitive.

Rich


Top
 Profile  
 
 Post subject: Re: grid leak radio
PostPosted: Aug Mon 15, 2011 10:41 pm 
Member

Joined: Dec Sun 23, 2007 8:12 pm
Posts: 56
well, I have a wire strung up in the basement about 30', I can get two stations on simple crystal radios with it. I have also install a small coupling cap inline with this antenna. Still no help when it is hooked up as a grid leak detector. Are you saying that a grid leak is not as good as a crystal radio?


Top
 Profile  
 
 Post subject: Re: grid leak radio
PostPosted: Aug Mon 15, 2011 11:19 pm 
Moderator

Joined: Jan Thu 01, 1970 1:00 am
Posts: 31398
Location: Livermore, CA
Best to see a schematic but you have something like this. A tuned circuit coupled to grid #1 through 250-500 pf with a 2 meg grid leak resistor. Other end of tuned circuit ground/B-. Tube cathode grounded. Screen supplied positive voltage less than the plate. Phones connect from plate to B+. Should bypass plate to B+ with a cap, .01 mf or so.

You should be able to receive at least the two stations.

For regen you need a feedback coil between plate and phones connection. This coil needs to be by the tuned citrcuit with proper polarity.

Being remote cutoff a 35 may not be quite as good as a 24 but will work.

_________________
Norm


Top
 Profile  
 
 Post subject: Re: grid leak radio
PostPosted: Aug Mon 15, 2011 11:30 pm 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 7080
Location: S. Dartmouth MA 02748-1225 USA
I have a commercial one tube Grid Leak radio called an "Audiotone", works, just about as good as a loud crystal set...

GL

_________________
"Don't find fault, find a remedy"
MA lic. radio/tv technician #53401


Last edited by Chas on Aug Tue 16, 2011 7:32 pm, edited 1 time in total.

Top
 Profile  
 
 Post subject: Re: grid leak radio
PostPosted: Aug Tue 16, 2011 11:43 am 
Member

Joined: Dec Sun 23, 2007 8:12 pm
Posts: 56
Norm, That's what I have but I did not bypass the plate with the .01 cap. So that cap should go from the plate to B+? I am working from schematics from the "1935 Short Wave mauual", "Rocky's" regenerative radios book, "how to build the most popular 1 and 2 tube radios" and many others that I am sure you know of. I would like this to work on the broadcast band. I was looking at some drawings last night and saw some with a heated cathode that had a wire from the heater to the cathode. Is it nessary to connect the cathode to the heater? I am using DC from my power supply not AC to power the heater.


Top
 Profile  
 
 Post subject: Re: grid leak radio
PostPosted: Aug Tue 16, 2011 1:20 pm 
Moderator

Joined: Jan Thu 01, 1970 1:00 am
Posts: 31398
Location: Livermore, CA
Might keep hum down but not necessary to connect heater to cathode. Cathode must be connected to B-, ground.

What you have will work. Even if it isn't connected correctly would expect the tube to act as a diode. Should at least be as good as a crystal set.

_________________
Norm


Top
 Profile  
 
 Post subject: Re: grid leak radio
PostPosted: Aug Tue 16, 2011 2:02 pm 
Member

Joined: Dec Sun 23, 2007 8:12 pm
Posts: 56
I would think it would work also, must be something that I'm missing. I have also tried to just get a triode tube like a 27 to work, also with no luck. I can get them to amplify if I use a diode from the tunning circuit like a crystal radio, and that works good but I would like to get it to work with the grid leak.

Norm, could you post a diagram of the complete circuit? using an indirectly heated cathode type triode tube like a 27? And then a diagram of another circuit that would use my 35 tetrode tube? That way I would follow them to the letter and it should work. My problem may be that I am trying to adapt directly heated schematics to indirectly heated tubes.
But on the other hand, I have had the same problems with a '01A tube. So I don't know.
Thanks for the help


Top
 Profile  
 
 Post subject: Re: grid leak radio
PostPosted: Aug Tue 16, 2011 2:13 pm 
Moderator

Joined: Jan Thu 01, 1970 1:00 am
Posts: 31398
Location: Livermore, CA
Dave has some nice radio circuits here:

http://www.makearadio.com/tube/index.php

In the case of heater tubes cathode must be connected to B-. Other than that should be same as filament type circuits.

_________________
Norm


Top
 Profile  
 
 Post subject: Re: grid leak radio
PostPosted: Aug Tue 16, 2011 4:31 pm 
Member

Joined: May Tue 30, 2006 4:46 pm
Posts: 6217
Location: Santa Rosa, CA
I don't think Dave has any "non-regen" radios on his site. Grid leak detectors never got as popular as regen sets because they weren't nearly as sensitive.

Image

Rich


Top
 Profile  
 
 Post subject: Re: grid leak radio
PostPosted: Aug Tue 16, 2011 4:57 pm 
Moderator

Joined: Jan Thu 01, 1970 1:00 am
Posts: 31398
Location: Livermore, CA
Rich

You are right. Just need to leave off the plate feedback coil.

The second schematic, using a pentode, should have B+ on the screen.

Any idea why he doesn't receive stations? If two stations are received on a crystal set this circuit should be better.

_________________
Norm


Top
 Profile  
 
 Post subject: Re: grid leak radio
PostPosted: Aug Tue 16, 2011 5:18 pm 
Member

Joined: Dec Sun 23, 2007 8:12 pm
Posts: 56
Rich and Norm, the first one is the one I have built BUT I am not using an antenna coil with a grid coil, just one coil with the antenna at one end and ground at the other. I have installed the grid leak at the same end as the antenna and B- at the other along with the cathode. The only other change is, no output transformer, just headphones. (old brandes)
If I can get it to work without a reg coil, I may try to add one before the final assembly.
About the second drawing, although I have many pentodes I could use, I have one old 5 pin tube socket and would like to use it. only for looks. I'm tring to make something that would look like my AK 10C all mounted on a board with wires under it. I have a couple of 5 pin tetrodes and one nice looking globe 235 that I would like to use (only for looks) Also my tube manuals list the tetrodes with an amp factor of 200 to 400 if I remember but the triodes only have a factor of less than 10 if I remember. Am I reading that right?

Norm I have looked at Daves site and don't remember seeing any for tetrodes, I'll look again.


Top
 Profile  
 
 Post subject: Re: grid leak radio
PostPosted: Aug Tue 16, 2011 5:24 pm 
Member

Joined: Dec Sun 23, 2007 8:12 pm
Posts: 56
Norm, one other thing, what value is that cap from plate to B-? That is one thing I have not seen in other schematics.


Top
 Profile  
 
 Post subject: Re: grid leak radio
PostPosted: Aug Tue 16, 2011 5:47 pm 
Moderator

Joined: Jan Thu 01, 1970 1:00 am
Posts: 31398
Location: Livermore, CA
Tetrodes are handled same as pentodes except third grid in a pentode is connected to cathode.

Right tetrodes and pentodes will have more gain than triodes. Pentodes and tetrodes can have 2nd grid connected to plate. Then they are operated as a triode with less gain.

I put a .01 mf on the plate when using phones. You can use other values. Driving another tube rather than phones value could be less, .001mf?

_________________
Norm


Top
 Profile  
 
 Post subject: Re: grid leak radio
PostPosted: Aug Tue 16, 2011 5:51 pm 
Member

Joined: Dec Sun 23, 2007 8:12 pm
Posts: 56
Thanks Norm, I may have some time to play with it some more tonight when I get home.
Tom


Top
 Profile  
 
 Post subject: Re: grid leak radio
PostPosted: Aug Wed 17, 2011 12:31 am 
Member

Joined: Dec Sun 23, 2007 8:12 pm
Posts: 56
UPDATE: It works! thanks Norm and Rich, The key was the .01 cap accross the phones and a jumper from the heater to the cathode. After I got the triode to work with the grid leak I tosed in the tetrode 35 adjusted the heater voltage, connected up the grid and screen. That worked even better. I then addad a few turns as a regen coil and BOOM! the stations came in! I got about 8 or 10 stations with the basement antenna.
The only problem I have is the 1.75 amp draw on the heater of the '35 tube overloads my power supply, it is one of the regulated power supplies that Norm sent me the schematic for about 3 years ago. If I remember correctly, it is limmited to 1.5 amp output.


Top
 Profile  
 
 Post subject: Re: grid leak radio
PostPosted: Aug Wed 17, 2011 1:21 am 
Moderator

Joined: Jan Thu 01, 1970 1:00 am
Posts: 31398
Location: Livermore, CA
Great

You can run the heater off of AC. Another way to get more current is add a small value resistor across the regulator. You will still have regulation as long as load is fairly constant. This way the regulator can handle an amp and resistor the rest.

We could find a globe tube with 6.3 volt filament. Number 36 or 39/44 only draw .3 amps @ 6.3 volts and come in globe, although smaller than a 35.

_________________
Norm


Top
 Profile  
 
 Post subject: Re: grid leak radio
PostPosted: Aug Wed 17, 2011 1:37 am 
Member

Joined: Dec Sun 23, 2007 8:12 pm
Posts: 56
Yes, I have a '36 but it is a shoulder type tube and won't look as good. I do have 2.5 volt transformer I can use to run the heater do you think that would give me more hum? remember that I have a jumper from the heater to the cathode. I guess I could rectifiy it and put 2.5 DC on the heater. I would like to end up with a small detacated power supply made to look like a old type battery, somehow. First I will finalize the radio design, then design it to look like something that would have been built in the late 20's early 30's ( I understand the '35 did not come out untill the late 30's). Then I will worry about the power supply.

One more thing, I ended up with -.3 volts on the grid. is that OK?


Top
 Profile  
 
 Post subject: Re: grid leak radio
PostPosted: Aug Wed 17, 2011 3:31 pm 
Moderator

Joined: Jan Thu 01, 1970 1:00 am
Posts: 31398
Location: Livermore, CA
Your circuit does not add grid bias so -.3 volts is about right. This voltage is developed by the tube .

Number 35 was being advertised in April 1932, 70 Years of Radio Tubes and Valves, page68. That makes it even better as to time frame of your radio.

_________________
Norm


Top
 Profile  
 
 Post subject: Re: grid leak radio
PostPosted: Aug Fri 19, 2011 1:34 am 
Member
User avatar

Joined: Jun Wed 08, 2011 2:33 am
Posts: 3655
Location: Ohio 45177
I sort of assumed that a one tube regen set so it is not coupled enough to regenerate, was acting as perhaps, a sort of "grid leak" detector? I built a one tuber with a 201 once and I could get some locals in the headphones, even without the feedback level set for regeneration. Or actually, I might have used it as a grid leak rec. before adding the stuff to make a regen out of it. I forget. Worked as good as a xtal set, maybe a bit louder, with a long outdoor wire. But with all the extra bother, might as well go ahead and feed back some of the output and really blast your phones!


Top
 Profile  
 
Post New Topic Post Reply  [ 20 posts ] 

All times are UTC [ DST ]


Who is online

Users browsing this forum: No registered users and 4 guests



Search for:
Jump to:  




















Privacy Policy :: Powered by phpBB