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  #31  
Old 06-13-2018, 02:28 PM
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Ok the voltages, the 210 v is 211 v where there is 95 v I'm getting 97 v ?and the 2.5 v on tube 75 I'm getting 3.3 v and on the same tube the 2.3 v I'm getting 3.0 v .the 290 v on the rec tube I get 293 v. Minus 8 v I'm getting minus 14 v. The 90 v on 78 tube im getting 78 v . I would think the only one that's off a bit would be the output tube where the -8 v is -14 v and the voltage don't change with the volume being turned. I did check the volume pot which is .5 meg where it tests at .9 meg.

Last edited by timmy; 06-13-2018 at 02:43 PM.
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  #32  
Old 06-13-2018, 03:50 PM
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Did you check the 70 ohm and 250 ohm bias resistors? They set the -8 volts on the output tube.

jr
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  #33  
Old 06-13-2018, 04:34 PM
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Quote:
Originally Posted by jr_tech View Post
Did you check the 70 ohm and 250 ohm bias resistors? They set the -8 volts on the output tube.

jr
Yes I checked those, the 70 ohm is 69 ohms and the 250 is 265 ohms. If it's a weak signal causing the low volume I went and checked the ohms on all the coils except the can on top, they were good.

Last edited by timmy; 06-13-2018 at 04:38 PM.
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  #34  
Old 06-14-2018, 11:29 AM
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Now, I guess it's time to try some new tubes! Every thing else seems to be reasonably in order.
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  #35  
Old 06-14-2018, 12:34 PM
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I guess that I am somewhat concerned about the high resistance of the volume control... perhaps disconnect the wire to the center leg and jumper it to the high end of the control and see if volume improves.

jr
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  #36  
Old 06-14-2018, 02:42 PM
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No difference with the volume control. Is it possible that one of 2 Micas could be bad or shorted , 6 and 17 on the schematic. More so 17 right off the audio output tube.
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  #37  
Old 06-14-2018, 03:20 PM
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Possible.... sure, not the most likely failure, but worth checking.

Even though the volume is low, is the sound undistorted?

jr
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  #38  
Old 06-14-2018, 04:01 PM
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Originally Posted by jr_tech View Post
Possible.... sure, not the most likely failure, but worth checking.

Even though the volume is low, is the sound undistorted?

jr
The sound is like any other am radio not clear like fm. Typical am and even the solid state radio I have has the buzz in the audio when on am. Those Micas are 81 years old and even in the tvs Micas were thought that they don't go bad but they do. I could clip it and check if any ohms are present which would not be good. Other then tubes the Micas are it there's nothing else, there's not much to this radio. Other then that the audio is good just like the solid state radio.
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  #39  
Old 06-17-2018, 06:53 PM
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I've read posts about this 38-12 radio where a jack was put in to play other music so my question is, is it at all feasible to put a phone jack in this radio to plug into an I pod and listen to that music using the radio. If it's possible where would I be injecting the signal, which tube and what pins. And would one side of the input be chassis ground and the other to one of the tube pins. There is 1st IF and 2nd IF and audio amp, then goes to audio output. The first tube is the oscillator which I don't think that would be used for this purpose.
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  #40  
Old 06-26-2018, 12:37 PM
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Ok found the problem, the array of resistors to make up 190k bias resistor just didn't work but I found the right resistor and the volume is loud now. I also completed the iPod jack and that works great just flip the switch one way for iPod and the other way for am radio. Ok so it's upside down, it's this iPad.
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  #41  
Old 06-26-2018, 12:39 PM
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The other pic, and yes I did the cabinet over it was garbage befor and I should have taken befor pics.
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Last edited by timmy; 06-26-2018 at 06:10 PM.
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  #42  
Old 06-26-2018, 01:02 PM
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Good! so what was wrong with the 190k plate resistor? .... you measired a reasonable voltage on the plate of the 75 tube, 97 volts, IIRC, odd that it didn't work.

jr
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  #43  
Old 06-26-2018, 02:31 PM
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Originally Posted by jr_tech View Post
Good! so what was wrong with the 190k plate resistor? .... you measired a reasonable voltage on the plate of the 75 tube, 97 volts, IIRC, odd that it didn't work.

jr
i don't know but that resistor measured 186k but it was several to make up the value but for some reason it didn't work. I also changed the 490k that I put in since it was a 5 watt and it calls for a half watt so I now have a 470 half watt in there now. 5 watt was over kill.
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  #44  
Old 06-26-2018, 04:14 PM
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What does the 490k/5 watt measure?

jr
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  #45  
Old 06-26-2018, 05:32 PM
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What does the 490k/5 watt measure?

jr
The 5 watt resistor I put in was a power resistor but it is a 470k and that's what it measured yet it was not right. Mystery this 470 5 watt was the replacement for the 490k since the old resistor that was in there was at 1.2meg , to high.

Last edited by timmy; 06-26-2018 at 06:07 PM.
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