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Post by frank1956 on Thu Feb 26, 2015 2:37 pm

How y'all want me to proceeded??? Start a new thread, add to this one??? Etc etc


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Post by jerryhawthorne on Thu Feb 26, 2015 4:31 pm

Frank, I would say stay on this thread although it is long there is some good information that needs to be kept in place.  I am going to add another link to the schematic so people don't have to search back for it.  It seems to me that previous tests indicated the audio section is working with volume and volume control?  We are now trying to get a signal through the IF section correct?
Jerry

http://www.nostalgiaair.org/PagesByModel/494/M0003494.pdf

Some thoughts:
1. Signal generator is not working.
2. 12BA6 is defective, check voltages and report.
3. Detector section of 12AT6 is bad or miss wired.
4. Try inserting your sig gen set to 455 and modulation on to pin 6 of the 12AT6. This is essentially inserting the 455 straight to the detector and bypassing the 12BA6 IF amp.

We have not given up!
Jerry

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Post by Wildcat445 on Fri Feb 27, 2015 6:44 pm

Jerry, since you are taking the lead here, would you be good enough to review your interpretation of what is going on so the rest of us can catch up. I have no idea of what is going on, and I'll bet I'm not the only one. Very Happy

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Post by jerryhawthorne on Fri Feb 27, 2015 7:25 pm

Heck WC, I'm just trying to confirm from Frank if we have an understanding as to where we are at.  My interpretation from his work with Dr. Radio is that the audio section is working from a earlier post with some clever work from the Dr.  Now if he gets a good hum on the center tap of the volume pot (answer this question Frank) it appears that we need to move closer to the front end of the radio.  Nothing on using the signal generator is concerning.  I wish he could confirm that it working properly.  Heck set another working radio near it and hook the output clip for the generator  close to the antenna of the second radio and try tuning the generator to same radio frequency with the radio set to the same frequency, does he get a signal (tone) with the modulation turned on?  Good test.  Your signal generator is working.  Nada and something is wrong with the generator.  In this mode the generator is a transmitter at the set frequency, it won't reach far but as long as the output lead is close to the radio you should get the modulation tone.
WC, I'm not the sharpest knife on this stuff so I take a slow and logical approach to fixing radios and it seems to work.  I know people that can go straight to the problem due to experience.  Not me.
I will try to guide Frank but there a lot of smarter people out there.  Come on Frank, time to pony up and do some checking.
Best,  Jerry

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Post by Wildcat445 on Fri Feb 27, 2015 9:15 pm

We'll see what Frank has to report and go from there, I guess. Thanks for giving the update. Good luck guys.

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Post by frank1956 on Sat Feb 28, 2015 6:41 pm

Jerry just to clarify the signal generator is in working condition.

I am going to do quick synopsis of this radio

It is a Crosley model 58TK was not working when it was purchase. Replaced all capacitors, resistors, and electrolytic. Tubes where replaced as needed. Radio was cleaned top to bottom and all switches work. When radio was turned on there was/is a buzz being produced nothing else, no static no hint of a radio station trying to come in. I went back and replaced the first set of electrolytic with the same results.

Was conducting a signal generator test and shorted out radio, with Dr. Radio help was able to get it back up and running. Below is what I have done with the help of several individuals.

I posted two audio of the radio with and without the signal generator hooked up, believe me the signal generator is producing the tone, but at a very low pitch??

First Test: Radio fires up after swapping the 12AT6 tube out.. All tubes light up. Radio is on all the time via the jumper you recommended I install. Used test rig and with radio UNPLUGGED my music was heard through the speaker.

Second Test: Disconnected pins #1 & #7 from the 50B5 tube. Connected the .1 cap via the test rig to pin #7 50B5 tube and the other end of the test rig to the B-. Turned radio on and my music was heard loud and clear through the radio speaker. Test was a success!!!

The test rig worked great, music was heard very clearly on both test. Especial when I removed the connection from pin's #1 and #7 the 50B5 tube and connected the test rig to either one of the pin's the music was fairly loud with slight hum and the volume control worked like it is supposed to. With the signal generator test there is not a loud tone being produced through the generator, that is why I am having a hard time hearing it, not because of the hum. Though I do have to crank the volume up on the generator in order for it to produce a audible tone for these ears to hear it.


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Post by jerryhawthorne on Sun Mar 01, 2015 1:47 am

Frank thanks for the update. Try number 4 on my suggestion list.
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Post by frank1956 on Thu Mar 05, 2015 4:07 pm

Jerry,
Tried #4 on your list as suggested and nothing from the signal generator. Went back with another working radio just to make sure my signal generators was and still is working, no problems there. I did not get an tone out of the radio speaker that was produced by the signal generator!!


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Post by Wildcat445 on Thu Mar 05, 2015 4:28 pm

Did you have the 400 cycle modulation turned on?  You should hear the modulation note in the speaker. Pin 6 is actually behind the detector and is the grid for the first audio stage. Apparently, you have audio at the volume control, and this is the next step toward the front end of the radio. Good luck.

WC

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Post by jerryhawthorne on Thu Mar 05, 2015 6:56 pm

Just so we can watch the schematic another posting of the link.  It is getting old going back to look for it.  WC, I'm generally wrong but from the schematic, pin 6 of the detector/first AF amp is the detector.  It seems Frank has a working generator from his previous experiment with a working radio.  Of course this was tested at an RF frequency and not the IF frequency.  It could be Frank that your generator is not working on the lower IF (a different switch setting on your generator).  You should get a strong modulated hum at 455 on pin 6.  If not then you need to check component values around the detector section.  Does your generator have just an AF freqency (tone only) out?  Often a switch change or change of the probe attachment?  If so, try just the tone to the grid of the first AF section pin 1.  The same tube as the detector.  This is just another test of the generator and the audio section of the radio.  Schematic again.
Jerry

http://www.nostalgiaair.org/PagesByModel/494/M0003494.pdf

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Post by Wildcat445 on Thu Mar 05, 2015 7:08 pm

I blew the schematic up, and I was looking at pin 2. I apologize for the confusion. Pin 6 is one of the detector diodes. I think I'm finally on the same page as everybody else.

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Post by jerryhawthorne on Fri Mar 06, 2015 12:45 am

Welcome aboard WC. We can use all the help we can get. Right Frank? I indicated previously we could all add a little confusion to the discussion!
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Post by Wildcat445 on Fri Mar 06, 2015 1:30 am

I've managed to confuse myself, so I have confidence that I can help confuse Frank. Rolling Eyes

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Post by frank1956 on Wed Mar 11, 2015 5:42 pm

Jerry, WC,
Sorry for the the un- timely response, with the snow, my well going out, just have not had the time to get back on here. Any way I tried just putting the two leads from the signal generator next to the radio antenna without hooking anything up, no signal was produced through the speaker of the radio. I can do the same with a working radio and a tone is produced. Not sure of what else to do?? Thanks to all for there help on this.

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Post by Wildcat445 on Wed Mar 11, 2015 6:18 pm

Did you perform the test that Jerry recommended above?  If not, please do.  This will give us direction on what to do next.  You need to perform directed tests, not willy-nilly guessing. Good luck.

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Post by jerryhawthorne on Wed Mar 11, 2015 6:47 pm

Pin 6 please with the sig. gen. set at 455 with modulation on.  Tone?  If you have access to an oscilloscope things would be a lot easier to test you generator at that frequency. We now know it works at the higher AM band frequency.
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Post by jerryhawthorne on Thu Mar 12, 2015 5:11 pm

Frank, a little explanation is in order for us to understand your previous post. When you tested both the good radio and the bad radio, was your signal generator set to someplace on the AM band frequency? Could you change the sig. gen. frequency and track the tone on your working radio by moving the dial to the gen frequency?
We just want to be clear. It is really tough to do this remotely so to speak. If you were setting on the AM band frequency and the good radio worked, great. I would not suspect your radio you were working would. Only because we have not figured out yet what is wrong. We need to determine if your gen is working on the lower band that will supply your IF frequency. Try my previous test on pin 6. If you get a tone great, if not we still need to think about that tube and wiring or your gen doesn't work at that frequency.
Sorry about your cold issue out there and there are certainly things more important than fixing a dang radio.
Jerry
Someone smarter than me (everyone) might figure out how to test it at the IF frequency on your working radio. Looking at the gen output on an O'scope can see if it is working at that frequency. It is necessary to know it is working. Knowing, it allows us to continue forward to test other areas along the IF.
More confusion for you. Sorry. Perhaps someone else can suggest how to check that frequency on your working radio?
Jerry

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Post by Bill Cahill on Thu Mar 12, 2015 7:16 pm

In the absence of an oscilloscope, I know of no other way to test it.

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Post by frank1956 on Sun Mar 15, 2015 11:45 am

frank1956 wrote:Jerry,
Tried #4 on your list as suggested and nothing from the signal generator. Went back with another working radio just to make sure my signal generators was and still is working, no problems there. I did not get an tone out of the radio speaker that was produced by the signal generator!!


Frank

Jerry,
That was suggestion #4 on your list on page 17 I think. My results are stated above. My signal generator for both test was set at 455 and the tune dial was un-meshed.

Frank
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Post by frank1956 on Sun Mar 15, 2015 11:55 am

Jerry
I forgot to answer one one your question.

Could you change the sig. gen. frequency and track the tone on your working radio by moving the dial to the gen frequency? Yes
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Post by jerryhawthorne on Sun Mar 15, 2015 9:08 pm

Frank, back to my post of the 11th regarding Pin 6 please.
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Post by frank1956 on Sun Mar 22, 2015 4:31 pm

Is that pin 6 of the 12AT6??

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Post by jerryhawthorne on Sun Mar 22, 2015 5:28 pm

Yes Frank, I'm attaching a link to the schematic again for easy referral.  Pin 6 is the detector which will take and strip the carrier 455 KC away from the modulated tone and pass it on to the volume control for that nice tone. That is if I understand radio stuff which I'm not the best at.  If you get a tone, we know your sig gen is working at that frequency, if not, well, it is either that you have a problem with the gen or something in the circuit that goes from the detector plate, pin 6 and to the high side of the volume control.
Pitch in guys, I may be over my head.
Jerry
http://www.nostalgiaair.org/PagesByModel/494/M0003494.pdf

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Post by 75X11 on Sun Mar 22, 2015 8:04 pm

I would say that if Frank were unsure about a missing result, he could try the same test on a known working unit. Without too many pieces of test equipment there is always this confirmation. It looks like you are steering Frank straight, Jerry.
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Post by jerryhawthorne on Sun Mar 22, 2015 8:36 pm

Just thinking again for Frank and help from you guys, I wonder if he set his gen to 455 and a loop of wire or direct connection to his working radio (if it had a 455) IF and cranked the gen up to max output and tuned the radio to the lowest of its band he could force some of that signal through the radio tuned to 550 or so? I'm not at my place where I could try it. Just a crazy thought but it might prove his gen is working at the lower frequency. An O'scope would be really nice. Frank, do you know anyone local that has one?
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