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#1
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Philco radio cap problem
The Philco 41-842 that I needed help getting a diagram for is giving me problems .There is one particular electrolytic cap in the 1LB4 (output tube)heater line that keeps getting very hot. I have replaced it with a new, still tests good cap. The diagram calls for a 100 mf cap 25 volts and the original sectional cap had a 200mf 25 volt in there.I used my digital meter and it does not show ac from the plus or ground of the cap to chassis ground or with my test leads on the plus and ground of it. I show about 4 volts dc from the pos to ground. One side of the tube heater does go to a grid inside the tube.I am lost,since I am not overvolting the electro. and I am not showing AC either ,but if I unsolder one end and test it with my cap checker it shows good.There is also an electro. in the other leg of the heater and it stays cold.The radio is fully recapped, the original speaker is gone. I do not know what the resistance of the output trans. should be so I do not know if it is an issue.I do have a speaker currently hooked up to the secondary of the output Trans. and I have no sound , hum, anything.Any Ideas?
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#2
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I forgot to add that this is an AC/DC/Battery set. The cap in question even gets hot when there is only the rectifier tube in place. The other caps are not getting hot though. This is the second rect. tube I have tried. Both were nos and tested good on a tv-7 tester.It is a 117z6 tube.The only thing that I can think of is the switch is bad that is used when you want to run it with batteries. I do not understand the switch as far as how it is shown and what makes contact when. The reason is the switch to me looks different than the pic on the diagram. The diag. pic shows 3 rows of 4 connections with 2 extra contacts apart from the rest and my switch has 4 rows of 3 connections without the extras.
Last edited by radio nut; 09-24-2009 at 10:27 PM. Reason: need more info |
#3
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I could not find a listing for a 41-842 but did find a schematic for a 42-482, If you are not running the cap at more than the rated voltage, about the only other thing that could make it get hot is incorrect polarity. Double check it.
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#4
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These are a bit safer than the notorious hot chassis models. Of course if that capacitor to chassis shorts then all bets are off. There are special caps for that purpose. Look at the chassis and try to find where the points for this floating ground are. Are you using an isolation transformer? Recommended regardless of the set. |
#5
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Audiokarma |
#6
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I would first verify the power supply. Check for B+ and filament voltages. And then work forward to the output stages. You still have that hot capacitor that maybe an issue. |
#7
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Another possibility you should consider is that there may have been others before you. Changes may have been made and not necessarily the right ones.
You can check against the schematic but that raises the possibility that there may have been production changes. In which case the schematic might not match. |
#8
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What voltage do you measure directly across the capacitor, from positive terminal to negative terminal, not to chassis ground.
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#10
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Last edited by radio nut; 09-26-2009 at 01:26 PM. Reason: added more info |
Audiokarma |
#11
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Here is a lower res version of the 41-842 schematic from another thread:
http://videokarma.org/showthread.php?t=246027 I have an AC-DC/battery set too so I'm interested in this. Last edited by rollei35guy; 09-25-2009 at 07:05 AM. |
#12
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Yes to the variac. yes again to the 125 line voltage.I will start where you stated. I did notice That at least one of the heater lines did junction to a couple of caps parallel to a IF trans. I wonder if those mica or ceramic caps are bad.I will keep you posted. The 82 volts was across the "hot" cap. If I go from pos of the hot cap to chassis ground I had 5 volts " if " I remember. My printer is dead. I usually print the diagram and then write all over it. Now I keep running to the computer and then back to the set.Right now I am more worried about my radio.
Last edited by radio nut; 09-26-2009 at 08:03 PM. Reason: more info again and I can't spell anymore! |
#13
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You know I just realized those 1Lxx tubes all have a directly heated cathode. That might affect the voltage readings you are getting. |
#14
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That would change the readings you get based on your meter settings and points you used as reference. Sorry I missed that. |
#15
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And remember this circuit does not have a chassis ground. Sure wish that schematic had some voltage readings. |
Audiokarma |
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