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  #16  
Old 10-03-2018, 11:07 AM
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If you smoke the selenium have a fan and an openable window ready...Selenium gas is VERY toxic as any chemist worth their salt will tell you.
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  #17  
Old 10-03-2018, 11:07 AM
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Oh , and , Thanks to the schematic graciously provided by Jim , I can see that there is a resistor between the rectifier and the first filter cap . That resistor , R32 , which is a 22 ohm 1 watt , is very likely what made the smoke . I'd still change the caps , and then check R32 as you may well find it open (infinite ohms) . That is also the resistor you'd want to increase the resistance of if you do try again to install a silicon diode .
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  #18  
Old 10-03-2018, 11:16 AM
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Originally Posted by init4fun View Post
Oh , and , Thanks to the schematic graciously provided by Jim , I can see that there is a resistor between the rectifier and the first filter cap . That resistor , R32 , which is a 22 ohm 1 watt , is very likely what made the smoke . I'd still change the caps , and then check R32 as you may well find it open (infinite ohms) . That is also the resistor you'd want to increase the resistance of if you do try again to install a silicon diode .
IIRC from when I worked on mine that resistor looks like a thin mica cap. It was color-coded in dots...It may or may not be the same on your set depending on production run and any possible previous repair work.
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  #19  
Old 10-03-2018, 03:22 PM
vortalexfan vortalexfan is offline
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Originally Posted by init4fun View Post
Your sending contrary messages , in one post you say "No audio but the tubes were lit" and in this post you say "The tubes not to light?" , , , So , which is it , ARE the tubes lit or are they not ?

Now , to get down to the troubleshooting , we need to talk about troubleshooting itself and what it means to diagnose and repair vacuum tube circuit electrical failures . The "Shotgun" method of replacing parts on a vague "It could be this part" notion is not the right way to go . A LOT of perfectly good parts end up replaced that way at great cost till the bad part is finally changed by the luck of the draw . Yes indeed changing out the failure prone electrolytics was a good action , but now that you've had the episode of reverse polarity and have no sound the best course would be to start over completely .

Were this my situation to rectify I'd start by replacing the filter capacitors again because as Electronic M and I have said , they very well could be damaged . Consider mounting a terminal strip to the chassis and attaching the new caps to it as in my picture . I'd put the Selenium rectifier back in the circuit (polarized correctly or you'll REALLY learn what it means to "let the magic smoke out"* !!!!!) and then with a DC voltmeter on a scale of 300 volts or higher , and the schematic diagram , see exactly where B+ voltage actually is and isn't . This of course presumes that the tubes ARE lit and you have no sound . If the tubes aren't lit , start with an AC voltmeter on at least 200 volts scale and using your schematic follow the tube's heater AC path till the open is found .

A multimeter , a schematic , and about 5 minutes are all it should take you to diagnose this , once you replace the filter caps and put the rest of the circuit back to original status . Once you've got it running if you want to eliminate the Selenium rectifier , fine , but DO install the proper dropping resistor for the excess voltage of the silicon diode , circuits have "as designed" operating voltages for a reason , and especially in electronics "somewhat higher" is just about never equated with "better" .

* If you don't already know , an overloaded or shorted Selenium rectifier lets out a noxious smoke that smells like a bucket of rotten eggs X 10 , so make damn sure you polarize the Selenium rectifier correctly , and also using your ohm meter mode of your multimeter make sure that the new caps you install are wired correctly and aren't presenting any kind of short circuit to the rectifier BEFORE you power it on again .....

No the tubes aren't glowing, what I thought was tubes glowing was actually the neon pilot lamp glowing.

As for the capacitors I ordered some new ones, and as for the selenium rectifier smell goes, I'm well aware what they smell like, that's why I wanted to eliminate it from the circuit so that it didn't have a chance to fail on me, and I did order a 47 ohm 2 watt resistor to install after the 1N4007 diode.

And I did use a terminal strip to install the electrolytic caps.

Last edited by vortalexfan; 10-03-2018 at 06:38 PM.
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  #20  
Old 10-03-2018, 05:34 PM
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I would start by testing the tubes... the heaters are in series, so if one heater is open, none will light up.

jr
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  #21  
Old 10-03-2018, 06:37 PM
vortalexfan vortalexfan is offline
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I would start by testing the tubes... the heaters are in series, so if one heater is open, none will light up.

jr
I did test the tubes that's the thing and they all tested good yet on my tube tester.

But they still don't glow.
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  #22  
Old 10-03-2018, 07:38 PM
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If the tubes are good, then I would use an ohm meter to trace around the heater string from one ac input to the other end of the string, following the path shown in the schematic. Could be a bad power switch, a broken wire, bad tube socket, dirty heater pins on a tube or whatever that is causing the open circuit.

This test can be done with the radio out of the cabinet and, of course unplugged.

jr
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  #23  
Old 10-03-2018, 07:53 PM
vortalexfan vortalexfan is offline
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Originally Posted by jr_tech View Post
If the tubes are good, then I would use an ohm meter to trace around the heater string from one ac input to the other end of the string, following the path shown in the schematic. Could be a bad power switch, a broken wire, bad tube socket, dirty heater pins on a tube or whatever that is causing the open circuit.

This test can be done with the radio out of the cabinet and, of course unplugged.

jr
Is the heater string marked on the schematic, or do I have to find it and Mark it myself?
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  #24  
Old 10-03-2018, 08:20 PM
dieseljeep dieseljeep is offline
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Originally Posted by Electronic M View Post
IIRC from when I worked on mine that resistor looks like a thin mica cap. It was color-coded in dots...It may or may not be the same on your set depending on production run and any possible previous repair work.
I haven't seen one of those resistors in ages. The flat Micamold resistors. They're both 470 ohm, 2 watt resistors.
I had to take mine apart today. It's a 7X03 chassis with OEM part code dates from late 1955.
The under chassis view from the OP shows the band selector switch is mounted on an angle with some form of a universal joint, which I thought was rather novel. Mine is mounted straight.
I unsoldered all the leads going to the back to make it a little easier to work on. Of course I made a drawing where each one went.
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  #25  
Old 10-03-2018, 08:34 PM
dieseljeep dieseljeep is offline
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Originally Posted by vortalexfan View Post
Is the heater string marked on the schematic, or do I have to find it and Mark it myself?
The heater string is shown toward the bottom of the schematic.
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  #26  
Old 10-03-2018, 08:55 PM
vortalexfan vortalexfan is offline
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Originally Posted by dieseljeep View Post
The heater string is shown toward the bottom of the schematic.
Ok, will check it out.

OK So I figured out that you were right there were some micamold resistors in the radio, two of them in fact, one that was coded Red-Red-Black, which is 22 ohms which is the R32 you were referring to on the schematic, and just like you suspected, it was blown wide open (it measured infinite) but the capacitor was fine yet, which I suspect that maybe the capacitors were actually spared any damage from the reversed diode by that resistor and that R32 was actually where the magic smoke came from.

So If I understand you guys correctly I'll need to replace R32 the 22 Ohm 1 watt resistor with a 47 Ohm 2 watt resistor if I intend to use the 1N4007 Diode in place of the Selenium Rectifier? Also would R32 being blown open be the cause for a dead radio? If so It seems the repair may be fairly easy to get this radio up and running again, a lot easier than we thought at first.

EDIT: there are actually 4 Micamold Resistors in the radio, and 3 of the 4 Micamold resistors are measuring as open, the two 470 Ohm 2 Watt Resistors (R30 and R31) attached to the one 22 MFD 160 Volt electrolytic capacitors are both measuring as open when measured in Ohms, but when measuring in kOhms it measures as .475 kOhms, and then the 22 Ohm resistor (R32) measures open no matter how you measure it.

Then all but one of my filter caps measure normally, meaning that they are not destroyed, but the third filter cap, (the 22 MFD 160 Volt cap that R30 and R31 are attached to) measures 29 PF and that's all that shows up on the capacitor tester, I don't even get an ESR value from my ESR meter/Capacitor tester, so I don't know if that means that the capacitor is shot or if its because it has resistors in line with the capacitor and its affecting the reading or what the deal is.
I know that when I still had the original can capacitor hooked up yet and when I went to test the capacitor lead that those two 470 ohm 2 Watt resistors were attached to (the 20 MFD 150 Volt lead that was marked with the triangle), it measured the same exact way, and the other two leads measured as they were supposed (even with resistors attached to their leads).

What's really bizarre is that R30 and R31 when measured as resistors they don't measure anything (they measure as open) but when measured as capacitors they measure 29 pF (MMFD) which is strange because why would resistors be measuring as capacitors?
Also for some reason the filter cap that those 2 resistors are attached to is also measuring as 29 pF on my capacitor/ESR tester but it doesn't give an ESR Value for that filter cap, which its like the capacitor tester is testing that capacitor as a mica or ceramic disc capacitor rather than an electrolytic capacitor like it should be, which is weird because all of the other filter caps test like they should, and they have resistors attached to them.
Even more strange is that this same phenomenon I'm describing that's happening with R30 and R31 and C1B that they are attached to also happened with the original can capacitor when it was attached still before i changed out the old can cap for the new filter caps.

So I'm not sure what's going on here...

Last edited by vortalexfan; 10-04-2018 at 02:12 AM.
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  #27  
Old 10-04-2018, 10:08 AM
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Electronic M Electronic M is offline
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Your DMM probably on its sub k ohm range has a max resistance measurement limit of 200-400 ohms and anything above that will read as infinite unless you move the range switch to a higher range. The 470 ohm resistors are probably fine.

The lytics measuring in the pF range are almost certainly open and defective. Picofarad range capacitance is easy to get from the cutoff leads of the cap, your instruments test leads, set wiring, etc. All can present a few dozen pF to the meter easily. Heck if you have a good amount of RCA A/V cables you'll find most have well over 100pF between center and shield. Any 2 conductors not connected to each other have some finite (possibly measurable) capacitance between them.
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  #28  
Old 10-04-2018, 10:14 AM
vortalexfan vortalexfan is offline
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Originally Posted by Electronic M View Post
Your DMM probably on its sub k ohm range has a max resistance measurement limit of 200-400 ohms and anything above that will read as infinite unless you move the range switch to a higher range. The 470 ohm resistors are probably fine.

The lytics measuring in the pF range are almost certainly open and defective. Picofarad range capacitance is easy to get from the cutoff leads of the cap, your instruments test leads, set wiring, etc. All can present a few dozen pF to the meter easily. Heck if you have a good amount of RCA A/V cables you'll find most have well over 100pF between center and shield. Any 2 conductors not connected to each other have some finite (possibly measurable) capacitance between them.
Ok. That makes sense, so it seems I only have 1 electrolytic cap to replace and the one resistor (R32) to replace and that's it. And the radio should be good again.
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  #29  
Old 10-04-2018, 10:49 AM
dieseljeep dieseljeep is offline
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If you smoke the selenium have a fan and an openable window ready...Selenium gas is VERY toxic as any chemist worth their salt will tell you.
How about a chemist that's on a low-sodium diet?
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  #30  
Old 10-04-2018, 10:53 AM
vortalexfan vortalexfan is offline
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How about a chemist that's on a low-sodium diet?
Ha! That's a good one!
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