My new project

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Re: My new project

Post by Dr. Radio on Sat Nov 15, 2014 11:29 pm

Part 3:

You are basically "force feeding" audio into the grid of the 50B5 tube. By disconnecting pin 1/7 from all other radio wiring, you are getting rid of all other audio paths. This is apart of the "divide and conquer" troubleshooting method.

Now, report back. If you don't get your audio to work, nothing you do further "upstream" in the radio is going to make a hill of beans to get you any closer to a working radio. This stage MUST PASS this test.

If it does not, you still have wiring issues, a bad tube, bad socket, bad audio output transformer etc etc etc.
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Re: My new project

Post by frank1956 on Sun Nov 16, 2014 9:52 am

Dr. Radio,
Thanks. I will proceed with the above test and let you know the out come. Thanks again.

Frank
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Re: My new project

Post by frank1956 on Mon Nov 17, 2014 2:37 pm

Radio unplugged audio tester connected, "successful" cheers  Now on to disconnection pins #1 & #7 50B5, hopefully same results!!!

Frank
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Re: My new project

Post by frank1956 on Mon Nov 17, 2014 4:37 pm

Dr. Radio,
Part's 2-3 all successful. Audio device worked like a charm, all aspect of the test passed with flying colors!!!  cheers  cheers

Frank
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Re: My new project

Post by 75X11 on Mon Nov 17, 2014 6:29 pm

That's some good news!
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Re: My new project

Post by frank1956 on Tue Nov 18, 2014 4:25 pm

Very Happy
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Re: My new project

Post by Wildcat445 on Tue Nov 18, 2014 5:19 pm

What is your next step, Frank?

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Re: My new project

Post by frank1956 on Tue Nov 18, 2014 5:51 pm

WC, Not sure what my next step is? I will have to wait and see. I am glad the two test I preformed were successful!!!


Frank
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Re: My new project

Post by 75X11 on Tue Nov 18, 2014 6:24 pm

While you wait for the dr. you might start thumbing through this that Ragwire has put up. It has a lot of the kind of information that will bring uou up to speed in troubleshooting and in the use of your test equipment.

http://www.tuberadioforum.com/t4046-free-download-complete-1948-nri-radio-course
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Re: My new project

Post by Wildcat445 on Tue Nov 18, 2014 8:21 pm

What is still not working right with your radio?

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Re: My new project

Post by 75X11 on Tue Nov 18, 2014 8:44 pm

I believe he has divided the functional second half of the radio from the malfunctioning first.
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Re: My new project

Post by frank1956 on Tue Nov 18, 2014 9:09 pm

Wildcat445 wrote:What is still not working right with your radio?

WC

No Dr. Radio was helping me troubleshoot the audio circuits. Which as I stated very successful!!!


Frank
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Re: My new project

Post by Dr. Radio on Tue Nov 18, 2014 9:15 pm

Yes, it is all about splitting up a project into manageable pieces to troubleshoot.

I'm glad to hear of your success Frank!

Although minor at this point, I would remove that 100 ohm resistor connected to the cathode of the 50B5 and replace it with a 150 ohm resistor. I have no idea why the schematic calls for a 100 ohm, that really too low of resistance and will prematurely shorten the life of the output tube.

The next step is to keep working backwards. We'll bring in the next stage. Let me decide on a game plan, I'm debating to leave the volume control out of the game plan or not for the next step.

See how nice it is to have the audio "tester" that pretty much anyone can get ahold of on the cheap ?
Smile
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Re: My new project

Post by frank1956 on Wed Nov 19, 2014 7:12 am

Dr. Radio,
Thanks. I have replaced the 100 ohm with 150 ohm resistor. I assume I can re-connected the wire's back to pins #1 & 7 on the 50B5 since the test passed??

Yea I did not have to go buy anything I had it here all along and did not realize it, until I got to thinking about it. It works like you said it would.

Frank
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Re: My new project

Post by Dr. Radio on Sat Nov 22, 2014 9:07 pm

Okay Frank, time to keep working "backwards". Time to "reintroduce" more of the audio amplification section back into the grand scheme of things.

The 12AT6 and related volume control wiring will be reconnected. So yes, to answer your earlier question, the wire(s) you removed from the 50B5 for testing may NOW be reconnected. Pay close attention to your wiring. No need for wiring errors to complicate things. Shocked

Here's the section to focus on:




You'll be "breaking" the connection from the "hot" side of the volume control. The hot is the input side from the radio's very own audio.  Your audio test rig will again be used to substitute a signal input to check more of the AF (audio frequency) circuitry.

Use the modified schematic below:




The hot side has been broken. In other words, the outer lug of the volume control that once connected to the network linking the 12BA6 and 12AT6 now only "sees" your audio source (through the protection capacitor of course). The common (ground) of your audio source once again connects to the common (B-) of the radio. You can connect that to the "low" side of the volume control since that already "sees" B- or any other convenient B- point, I just show it going to the "common" ground symbol to make it easy to read.

Other than this modification, all other wires can be put back to their proper points.

Now, when you turn the radio on and turn on your audio source, you should have ample volume. In fact, you will most likely have to turn down the volume on your audio test rig to keep things from distorting due to the high gain provided by your radio. The audio should be 'loud and proud' and you should be able to turn it up and down with the radio's own volume control.

Is the radio starting to act/sound like a radio? Let us know.
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Re: My new project

Post by frank1956 on Sun Nov 23, 2014 10:35 am

Dr. Radio,
Is this the test that you wanted me to do the first go around, just about the beginning of this thread? To connect it to where the 47k resistor, the .00025 cap and the 3.3M resistor all tie together on the volume control? Just want to make sure I understand the above, it sounds similar in nature.

Frank
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Re: My new project

Post by Dr. Radio on Sun Nov 23, 2014 12:15 pm

Frank,

Yes and no.


Yes, it is basically the same idea, but this time I want you to break the connection to the high side of the volume pot. The ONLY connection to the high side of the volume pot will be your audio test rig just as I showed you in the modified schematic.

All other connections should be kept together in the factory manner. In other words, if for example, you have 3 components that all tied to the high side of the volume pot, you keep them all tied together, but disconnected from the volume pot lug itself so you can inject YOUR signal there.
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Re: My new project

Post by frank1956 on Sun Nov 23, 2014 5:01 pm

Dr. Radio,
Thanks. Just an FYI the above test I mention did work as well. Was able to control the volume using the volume control. Other then the slight hum it has been producing everything else worked.
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Re: My new project

Post by frank1956 on Sun Nov 23, 2014 5:28 pm

Dr. Radio,
I dis-connected the the high side of the vol pot, by removing the 47K res, 3.3M res and the .00025 cap. The results were:

(1) My music came out of the speaker of the radio
(2) Volume was controlled with the radio's volume control.
(3) Radio still produce's a slight hum as in the beginning.

I believe this was the correct test procedure.

Frank
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Re: My new project

Post by 75X11 on Sun Nov 23, 2014 7:42 pm

Looks like you are getting there!
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Re: My new project

Post by Dr. Radio on Fri Nov 28, 2014 9:10 pm

Frank,

The good news is it sounds like your AF circuitry is working fine. The bad news we still have "half" the radio to investigate. The RF/IF sections are suspect.

If you haven't done so already, reconnect everything as the factory had it (with your volume control, output tube wiring etc).

The next step is signal substitution.

Get out your RF signal generator. Connect the ground lead of the generator to the B- connection of the radio.

Connect the positive or "hot" lead of your generator to one leg of a .1 uF @ 600 volt capacitor. The other leg of the capacitor will connect to pin 1 of the 12BA6 tube (grid).

Turn the shaft of the tuning capacitor so it's at minimum capacity...so the "blades" of the capacitor are fully UN-meshed.

Turn on the generator and set it for 455 kHz (the IF frequency of the radio). Set your generator so it's internal tone is sent out (modulated tone.....beeeeeeeeep).


Turn the radio on. Do you hear the tone out the speaker?
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Re: My new project

Post by Bill Cahill on Sat Nov 29, 2014 5:21 pm

Hey, is this an ac dc radio? If so, you must have a capacitor between grounds..

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Re: My new project

Post by Dr. Radio on Sat Nov 29, 2014 10:44 pm

Bill Cahill wrote:Hey, is this an ac dc radio? If so, you must have a capacitor between grounds..

Welcome Back Bill!

It *should* be a moot point. I asked earlier about the use of an isolation transformer for safety sake as well as negating the need for a cap between the radio ground and the signal generator ground.

It is dangerous to assume, but I would think at this point Frank has one after aligning his other radios.

Frank?

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Re: My new project

Post by frank1956 on Sun Nov 30, 2014 9:12 am

Dr. Radio,
Yea I have been using a .1 cap @ 630v.

I went to preform the signal generator test, and now have another problem. (hopefully small). It was a dumb move on my part as well as attention to detail. I connected the ground of the signal generator as instructed to pin #2 the B- of the 12BA6 (instead of connection to the B- of the volume control) tube and the HOT to pin #1 of the 12BA6 tube. Being that the two pin's are very close together I did not realize the two alligator clips were making contact, and when I turned the radio on I had a big puff of smoke (a great big short). Turned everything off and disconnected the generator connections.

Now I have zero power if any to the radio, not sure what I shorted out or if I screwed the radio up for good.  Question  Sorry to be such a pain.
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Re: My new project

Post by 75X11 on Sun Nov 30, 2014 10:24 am

While you are waiting on Dr. Radio, you might want to check each of the resistors in the area. They can be big emitters of smoke.
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Re: My new project

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