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 Post subject: Finally drew up the schematic for my Homebrew
PostPosted: Feb Sat 25, 2012 9:37 pm 
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Location: Ennismore, Ontario
Years ago I bought a HomeBrew battery radio and have never been able to get it to play. I have tried hooking it up many times and some folk here have tried to help. I knew I needed to draw up the circuit to try to make sense of what was there and maybe allow others to advise on how I could get this radio to play. Finally drew it up. I have added the voltages I used listed near the terminals. All I get right now is a loud whistle which is linked somehow to the heaters. The pitch changes as I alter the filament voltage.
I don't even know if this radio ever worked. I am also wondering if I should build a radio that would work using the parts I have instead of trying to reverse engineer it.
So looking for insight.

First the picture of the radio...

Image

Image

Image

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Brian
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 Post subject: Re: Finally drew up the schematic for my Homebrew
PostPosted: Feb Sat 25, 2012 9:55 pm 
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Fantastic! I like it. You even used the old school tube symbols. Good job. I have examined your circuit and it looks to me like it's a regenerative scheme (feedback via capacitor C1)with no local oscillator and hence no super-hetrodyning or resulting IF stage. A receiver of this type, just like a crystal set, would "hear" several stations at the same time. Since in this day & age there are so many powerful and closely spaced stations, I would probably build something that includes a local oscillator and subsequent IF stages. If it ever originally worked, probably not well since there is no RF coil tuning. I'm a bit perplexed as to why anyone would attempt to tune plate circuits. Looks like you have the Tiger by the tail. Nice cabinet!

I'm more interested in the radio below it. What do you have there? Could you take a better photo?


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 Post subject: Re: Finally drew up the schematic for my Homebrew
PostPosted: Feb Sat 25, 2012 10:25 pm 
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Thanks - but would it work?

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 Post subject: Re: Finally drew up the schematic for my Homebrew
PostPosted: Feb Sun 26, 2012 1:46 am 
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I'm having trouble following the battery connections.

"A" battery is 5 Volt, "C" battery is 9 Volt, and there are three "B" batteries, 135 Volt, 67 Volt, and 45 Volt. Ok.

I presume the "-" on the same term as -9 Volt is C- and I see A+ and A-. Where is B- and what is Bat+ and Bat- ?


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 Post subject: Re: Finally drew up the schematic for my Homebrew
PostPosted: Feb Sun 26, 2012 2:14 am 
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It's obviously an unfinished project, and it will not output anything intelligible from what I can see. Where did you get this?


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 Post subject: Re: Finally drew up the schematic for my Homebrew
PostPosted: Feb Sun 26, 2012 3:52 am 
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Joined: Jan Mon 30, 2012 2:03 am
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Location: tacoma wa
this radio could never have worked as drawn;

(1) your tuning cap is connected at one end to the primary of the rf coil and at the other end to the secondary of this coil.There is no tank circuit to
tune a station to resonance.
(2) There appears to be no ground anywhere on this radio.
(3) There is no rf bypass cap at the plate output of the detector. The rf can only feedback to the filiament circuit. This might be the reason why the pitch changes as you alter filiament voltage.
(4) A grid leak always bypasses the excess negative bias on the detector grid to ground. I dont see that happening here. Also, C1, instead of biasing
the detector grid appears to be feeding all the plate energy of the preceeding tube (which is completely untuned) to the detector grid.
I am not a radio engineer so some of my observations could be wrong. Maybe someone could confirm or refute some of this.
I think this radio could work if rewired correctly.


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 Post subject: Re: Finally drew up the schematic for my Homebrew
PostPosted: Feb Sun 26, 2012 8:55 am 
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I'm not up on receivers either, and don't understand how the front end was intended to function, but the detector looks workable to me. C1 feeds RF to the grid but the grid leak should have it biased near the onset of positive grid drive so RF peaks will clamp there and if the envelop varies, I.E. AM, then bias shifts with the audio, and so does plate current. If the plate choke is then appropriately sized to block RF, but pass audio, we have audio passed onto the output stage through the coupling transformer with RF remaining on the plate which, I presume, is intentional for regen back to the front end I don't understand.


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 Post subject: Re: Finally drew up the schematic for my Homebrew
PostPosted: Feb Sun 26, 2012 2:34 pm 
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Location: Ennismore, Ontario
Blustar1 wrote:
It's obviously an unfinished project, and it will not output anything intelligible from what I can see. Where did you get this?


I picked this up years ago, tried to draw the circuit but could not. Just recently opened it up again and set it to paper. I could not see how it would work either but drew it up as I bought it. Cabinet is nice though. Will look for a circuit that I can put in there that uses the 2 variable caps and 2 pots as I would like to keep the front the way it is. Anyone have a simple radio circuit that I could use?

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 Post subject: Re: Finally drew up the schematic for my Homebrew
PostPosted: Feb Sun 26, 2012 2:50 pm 
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Flipperhome wrote:
I'm having trouble following the battery connections.

"A" battery is 5 Volt, "C" battery is 9 Volt, and there are three "B" batteries, 135 Volt, 67 Volt, and 45 Volt. Ok.

I presume the "-" on the same term as -9 Volt is C- and I see A+ and A-. Where is B- and what is Bat+ and Bat- ?



I had B- hooked to A+/Bat-. I did not have a B+ hooked up to the A-/Bat/C+ terminal.

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 Post subject: Re: Finally drew up the schematic for my Homebrew
PostPosted: Feb Sun 26, 2012 3:03 pm 
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Location: Ennismore, Ontario
R. Jepsen wrote:
I'm more interested in the radio below it. What do you have there? Could you take a better photo?


The radio below it is a Rogers 7R832. I have refinished it and replaced the top veneer twice now and it is still bubbling so I will need to strip and redo the veneer again this summer. Radio has great sound.

Image

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 Post subject: Re: Finally drew up the schematic for my Homebrew
PostPosted: Feb Sun 26, 2012 11:35 pm 
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Wow! Fantastic, I like it. It even has a magic eye tube. Do you have the powdered and pampered dame that goes with the radio?


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 Post subject: Re: Finally drew up the schematic for my Homebrew
PostPosted: Feb Sun 26, 2012 11:45 pm 
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R. Jepsen wrote:
Wow! Fantastic, I like it. It even has a magic eye tube. Do you have the powdered and pampered dame that goes with the radio?


What is that?
No powdered one here. A pampered one, in my eyes, maybe.

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 Post subject: Re: Finally drew up the schematic for my Homebrew
PostPosted: Feb Tue 28, 2012 1:30 am 
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Well I bet it sounds as good at it looks. How long have you been a collector? I see another vintage radio next to it. I'm just starting and only have a few mickey mouse things.


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 Post subject: Re: Finally drew up the schematic for my Homebrew
PostPosted: Feb Tue 28, 2012 2:43 am 
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R. Jepsen wrote:
Well I bet it sounds as good at it looks. How long have you been a collector? I see another vintage radio next to it. I'm just starting and only have a few mickey mouse things.


It does have good sound. Here is a picture of the wall that has the radios. I have about 50 spread out thru the house.

Image

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 Post subject: Re: Finally drew up the schematic for my Homebrew
PostPosted: Feb Tue 28, 2012 2:56 am 
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Wow! Impressive.

I like the fish tank radio :lol:


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 Post subject: Re: Finally drew up the schematic for my Homebrew
PostPosted: Feb Tue 28, 2012 3:30 am 
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Flipperhome wrote:
Wow! Impressive.

I like the fish tank radio :lol:


That's my wife's fish tank. We have 3 tanks up to a 35 gallon including a salt water tank. I wish this one was gone - it takes up a radio spot.

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 Post subject: Re: Finally drew up the schematic for my Homebrew
PostPosted: Feb Wed 29, 2012 5:45 am 
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Quote:
I'm not up on receivers either, and don't understand how the front end was intended to function


It's nothing more than an untuned, broadband RF amp- just uses an inductor rather than a resistor on the grid. If it were me rebuilding this I'd make the first RF amp and detector tuned, both in their grid circuits. No reason in the world this couldn't be a decent radio if this were done. If you wanted to get fancy, make the RF amp do double duty as an audio amp- commonly known as a reflex circuit.

Scott Todd


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 Post subject: Re: Finally drew up the schematic for my Homebrew
PostPosted: Feb Wed 29, 2012 6:45 am 
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N0BST wrote:
It's nothing more than an untuned, broadband RF amp- just uses an inductor rather than a resistor on the grid. If it were me rebuilding this I'd make the first RF amp and detector tuned, both in their grid circuits. No reason in the world this couldn't be a decent radio if this were done. If you wanted to get fancy, make the RF amp do double duty as an audio amp- commonly known as a reflex circuit.
Well, yes, I figured the front end was an untuned RF amp and, like you, I'd think it better tuned. It's the odd tank and regen I don't quite get.

All this 'radio talk' is getting me interested in putting together a simple one tube radio 'kit' for my nephew, like maybe Norm's 12K5.


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 Post subject: Re: Finally drew up the schematic for my Homebrew
PostPosted: Feb Wed 29, 2012 8:21 pm 
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If you're not opposed to solid state why not use an MK-484 AM IC. You can still use the two tubes one as an antenna preamp and one as a tuned RF stage. One control can be repurposed as an AGC control while the other control can be the volume control.

You would need to find or construct a couple RF transformers that will allow the stages to be coupled to each other with the secondary of the transformers forming a tuned circuit with the variable capacitors so that the AM broadcast band can be tuned.

For a schematic look at the last page of this topic viewtopic.php?f=12&t=185510


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 Post subject: Re: Finally drew up the schematic for my Homebrew
PostPosted: Mar Thu 01, 2012 12:51 am 
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I'm not 'opposed' to solid state, just ICs. :lol:

Actually, I'm not 'opposed' to those either it's just that this particular hobby interest is 'discrete' design and I find tubes more 'fun' because of the different design approach. I realize you can do 'the same thing' with transistors but like doing it 'the old fashioned way'.

The attractiveness to Norm's 12k5 is utter simplicity, especially for my nephew who is still trying 'everything' so I'm 'experimenting' with his 'interest' in electronics.

I already did one radio a while back: a crystal job made from household items, except the 1N34. I thought trying a cat whisker would be too tedious to keep his interest (not to mention I didn't have one). Wound the coil from spare wire around a large box and made a variable cap with tin foil on one of those 'computer network card' boxes with an outer decorative sleeve. Foil on one side covered with clear packing tape and foil inside the slide cover, which was tacked down to a board. Slide the inner box in and out for station tuning.

Didn't have high impedance headphones either so I wired it to a 1/4 jack and we used the computer mic input for an audio amp.

I'm tempted to have him wind the coil for this one but think that might be too tedious again, and I've got a loopstick anyway. The box cap worked but was a bit touchy because the cardboard flexes some, and I've got a plastic variable anyway. The only thing I don't have is the 12K5.


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