Overheating power transformer?
5/23/2013 1:06:17 PMBill B.(106667:0)
Hello: I just finished my electrical restoration of a Sears 101.825-4 chassis and it seems the power transformer is running way too hot.It gets almost hot enough to sizzle spit on, and is definitely too hot to leave your hand on. I replaced all capacitors including the electrolytics, except for one .05 which is underneath the tuner assembly and I cannot get to it. Also I did not open up any IF cans to replace caps in there. I read 335 VDC off pin 7 on the 7Z4 rectifier. Each side of the power transformer reads 312 VAC to ground and 621 VAC across the outside leads. I get 306 VDC off pin 2 ( the plate ?) of the 7C5 output tube, and 260VDC off pin 3 ( Grid 1 ? ) and .23 volts off pin 6 ( grid 2? ) The AF tube (driver ) reads 60.5 VDC volts on pin 2 ( the plate ) and .68 VDC on the grid. There is a 330 ohm ( measures 410 ohm ) 1 watt resistor from the cathode of the output tube to ground with a 25 mfd electrolytic across it. That resistor gets too hot to touch ! The power resistors R-32 and R-41 2K 5 watt wirewound also get too hot to touch. The 7Z4 rectifier gives off an awful lot of heat, but I'm gonna assume that's normal ? I replaced two tubes...The 7A6 FM discriminator and the 7C7 FM 3rd. IF. The radio plays beautifully on FM and AM with no hum or any wierd noises from the speaker. It does have a tendency to drift just a tad after it warms up. Any ideas or thought would surely be appreciated.
-Bill B.
-Bill B.
5/23/2013 1:36:01 PMNorm Leal(106668:106667)
Hi Bill
I left my comment on ARF:
http://www.antiqueradios.com/forums/viewtopic.php?f=6&t=223434
Norm
:Hello: I just finished my electrical restoration of a Sears 101.825-4 chassis and it seems the power transformer is running way too hot.It gets almost hot enough to sizzle spit on, and is definitely too hot to leave your hand on. I replaced all capacitors including the electrolytics, except for one .05 which is underneath the tuner assembly and I cannot get to it. Also I did not open up any IF cans to replace caps in there. I read 335 VDC off pin 7 on the 7Z4 rectifier. Each side of the power transformer reads 312 VAC to ground and 621 VAC across the outside leads. I get 306 VDC off pin 2 ( the plate ?) of the 7C5 output tube, and 260VDC off pin 3 ( Grid 1 ? ) and .23 volts off pin 6 ( grid 2? ) The AF tube (driver ) reads 60.5 VDC volts on pin 2 ( the plate ) and .68 VDC on the grid. There is a 330 ohm ( measures 410 ohm ) 1 watt resistor from the cathode of the output tube to ground with a 25 mfd electrolytic across it. That resistor gets too hot to touch ! The power resistors R-32 and R-41 2K 5 watt wirewound also get too hot to touch. The 7Z4 rectifier gives off an awful lot of heat, but I'm gonna assume that's normal ? I replaced two tubes...The 7A6 FM discriminator and the 7C7 FM 3rd. IF. The radio plays beautifully on FM and AM with no hum or any wierd noises from the speaker. It does have a tendency to drift just a tad after it warms up. Any ideas or thought would surely be appreciated.
:-Bill B.
:
5/23/2013 1:47:28 PMEdd(106670:106667)
Then PULL the AF output tubes and place the rectifier tube back in. By this time, I may then have that units schematic and can give you more exacting /further feedback.
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:Hello: I just finished my electrical restoration of a Sears 101.825-4 chassis and it seems the power transformer is running way too hot.It gets almost hot enough to sizzle spit on, and is definitely too hot to leave your hand on. I replaced all capacitors including the electrolytics, except for one .05 which is underneath the tuner assembly and I cannot get to it. Also I did not open up any IF cans to replace caps in there. I read 335 VDC off pin 7 on the 7Z4 rectifier. Each side of the power transformer reads 312 VAC to ground and 621 VAC across the outside leads. I get 306 VDC off pin 2 ( the plate ?) of the 7C5 output tube, and 260VDC off pin 3 ( Grid 1 ? ) and .23 volts off pin 6 ( grid 2? ) The AF tube (driver ) reads 60.5 VDC volts on pin 2 ( the plate ) and .68 VDC on the grid. There is a 330 ohm ( measures 410 ohm ) 1 watt resistor from the cathode of the output tube to ground with a 25 mfd electrolytic across it. That resistor gets too hot to touch ! The power resistors R-32 and R-41 2K 5 watt wirewound also get too hot to touch. The 7Z4 rectifier gives off an awful lot of heat, but I'm gonna assume that's normal ? I replaced two tubes...The 7A6 FM discriminator and the 7C7 FM 3rd. IF. The radio plays beautifully on FM and AM with no hum or any wierd noises from the speaker. It does have a tendency to drift just a tad after it warms up. Any ideas or thought would surely be appreciated.
:-Bill B.
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5/23/2013 3:03:13 PMBill B.(106671:106670)
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::Hello: I just finished my electrical restoration of a Sears 101.825-4 chassis and it seems the power transformer is running way too hot.It gets almost hot enough to sizzle spit on, and is definitely too hot to leave your hand on. I replaced all capacitors including the electrolytics, except for one .05 which is underneath the tuner assembly and I cannot get to it. Also I did not open up any IF cans to replace caps in there. I read 335 VDC off pin 7 on the 7Z4 rectifier. Each side of the power transformer reads 312 VAC to ground and 621 VAC across the outside leads. I get 306 VDC off pin 2 ( the plate ?) of the 7C5 output tube, and 260VDC off pin 3 ( Grid 1 ? ) and .23 volts off pin 6 ( grid 2? ) The AF tube (driver ) reads 60.5 VDC volts on pin 2 ( the plate ) and .68 VDC on the grid. There is a 330 ohm ( measures 410 ohm ) 1 watt resistor from the cathode of the output tube to ground with a 25 mfd electrolytic across it. That resistor gets too hot to touch ! The power resistors R-32 and R-41 2K 5 watt wirewound also get too hot to touch. The 7Z4 rectifier gives off an awful lot of heat, but I'm gonna assume that's normal ? I replaced two tubes...The 7A6 FM discriminator and the 7C7 FM 3rd. IF. The radio plays beautifully on FM and AM with no hum or any wierd noises from the speaker. It does have a tendency to drift just a tad after it warms up. Any ideas or thought would surely be appreciated.
::-Bill B.
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: : : :  : : : : : : : :Sir Bill . . . . : : :I don’t have that Samuels schematic at hand and initially would only suggest to have all of the tubes installed in the set and only unplug the rectifier tube OUT of the set and see if the power t- former is cool after about an hour run time with it only being subjected to filamental circuitry loading and with NO B+ being created. : : : :Then PULL the AF output tubes and place the rectifier tube back in. : : :Initially, spot check the main B+ again just to see that the minimal power pull / loading of only the tubes present is not skyrocketing the B level at the first main filter electrolytic. : : :Then run an hour and see if this test run is still leaving a normal temperature for the power t-former, as was found before. : : :If you then move on to full tube installation for a test run and find overheating, the set must have an excess current pull in the AF power stage circuitry, by virtue of that mentioned overheating cathode resistor. : : : :By this time, I may then have that units schematic and can give you more exacting /further feedback. : : : : : : :73's de Edd : : : : : :Blessed is he who expects no gratitude, for he shall not be disappointed. : : :  : : : |
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::Hello: I just finished my electrical restoration of a Sears 101.825-4 chassis and it seems the power transformer is running way too hot.It gets almost hot enough to sizzle spit on, and is definitely too hot to leave your hand on. I replaced all capacitors including the electrolytics, except for one .05 which is underneath the tuner assembly and I cannot get to it. Also I did not open up any IF cans to replace caps in there. I read 335 VDC off pin 7 on the 7Z4 rectifier. Each side of the power transformer reads 312 VAC to ground and 621 VAC across the outside leads. I get 306 VDC off pin 2 ( the plate ?) of the 7C5 output tube, and 260VDC off pin 3 ( Grid 1 ? ) and .23 volts off pin 6 ( grid 2? ) The AF tube (driver ) reads 60.5 VDC volts on pin 2 ( the plate ) and .68 VDC on the grid. There is a 330 ohm ( measures 410 ohm ) 1 watt resistor from the cathode of the output tube to ground with a 25 mfd electrolytic across it. That resistor gets too hot to touch ! The power resistors R-32 and R-41 2K 5 watt wirewound also get too hot to touch. The 7Z4 rectifier gives off an awful lot of heat, but I'm gonna assume that's normal ? I replaced two tubes...The 7A6 FM discriminator and the 7C7 FM 3rd. IF. The radio plays beautifully on FM and AM with no hum or any wierd noises from the speaker. It does have a tendency to drift just a tad after it warms up. Any ideas or thought would surely be appreciated.
::-Bill B.
5/23/2013 3:08:12 PMBill B.(106672:106671)
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:::Hello: I just finished my electrical restoration of a Sears 101.825-4 chassis and it seems the power transformer is running way too hot.It gets almost hot enough to sizzle spit on, and is definitely too hot to leave your hand on. I replaced all capacitors including the electrolytics, except for one .05 which is underneath the tuner assembly and I cannot get to it. Also I did not open up any IF cans to replace caps in there. I read 335 VDC off pin 7 on the 7Z4 rectifier. Each side of the power transformer reads 312 VAC to ground and 621 VAC across the outside leads. I get 306 VDC off pin 2 ( the plate ?) of the 7C5 output tube, and 260VDC off pin 3 ( Grid 1 ? ) and .23 volts off pin 6 ( grid 2? ) The AF tube (driver ) reads 60.5 VDC volts on pin 2 ( the plate ) and .68 VDC on the grid. There is a 330 ohm ( measures 410 ohm ) 1 watt resistor from the cathode of the output tube to ground with a 25 mfd electrolytic across it. That resistor gets too hot to touch ! The power resistors R-32 and R-41 2K 5 watt wirewound also get too hot to touch. The 7Z4 rectifier gives off an awful lot of heat, but I'm gonna assume that's normal ? I replaced two tubes...The 7A6 FM discriminator and the 7C7 FM 3rd. IF. The radio plays beautifully on FM and AM with no hum or any wierd noises from the speaker. It does have a tendency to drift just a tad after it warms up. Any ideas or thought would surely be appreciated.
:::-Bill B.
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Edd: I pulled the rectifier tube and ran the set for an hour and a half and the transformer is warm/hot but you wont get burned and it definitely won't sizzle spit. Now I should pull the output tube and check the B+ voltages again and what does that tell me if they go way up or way down? Thanks for the help.
-Bill B.
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:: :: :: :: :: :: :: :: :: :: :: ::Sir Bill . . . . :: :: ::I don’t have that Samuels schematic at hand and initially would only suggest to have all of the tubes installed in the set and only unplug the rectifier tube OUT of the set and see if the power t- former is cool after about an hour run time with it only being subjected to filamental circuitry loading and with NO B+ being created. :: :: :: ::Then PULL the AF output tubes and place the rectifier tube back in. :: :: ::Initially, spot check the main B+ again just to see that the minimal power pull / loading of only the tubes present is not skyrocketing the B level at the first main filter electrolytic. :: :: ::Then run an hour and see if this test run is still leaving a normal temperature for the power t-former, as was found before. :: :: ::If you then move on to full tube installation for a test run and find overheating, the set must have an excess current pull in the AF power stage circuitry, by virtue of that mentioned overheating cathode resistor. :: :: :: ::By this time, I may then have that units schematic and can give you more exacting /further feedback. :: :: :: :: :: :: ::73's de Edd :: :: :: :: :: ::Blessed is he who expects no gratitude, for he shall not be disappointed. :: :: :: :: :: :: |
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:::Hello: I just finished my electrical restoration of a Sears 101.825-4 chassis and it seems the power transformer is running way too hot.It gets almost hot enough to sizzle spit on, and is definitely too hot to leave your hand on. I replaced all capacitors including the electrolytics, except for one .05 which is underneath the tuner assembly and I cannot get to it. Also I did not open up any IF cans to replace caps in there. I read 335 VDC off pin 7 on the 7Z4 rectifier. Each side of the power transformer reads 312 VAC to ground and 621 VAC across the outside leads. I get 306 VDC off pin 2 ( the plate ?) of the 7C5 output tube, and 260VDC off pin 3 ( Grid 1 ? ) and .23 volts off pin 6 ( grid 2? ) The AF tube (driver ) reads 60.5 VDC volts on pin 2 ( the plate ) and .68 VDC on the grid. There is a 330 ohm ( measures 410 ohm ) 1 watt resistor from the cathode of the output tube to ground with a 25 mfd electrolytic across it. That resistor gets too hot to touch ! The power resistors R-32 and R-41 2K 5 watt wirewound also get too hot to touch. The 7Z4 rectifier gives off an awful lot of heat, but I'm gonna assume that's normal ? I replaced two tubes...The 7A6 FM discriminator and the 7C7 FM 3rd. IF. The radio plays beautifully on FM and AM with no hum or any wierd noises from the speaker. It does have a tendency to drift just a tad after it warms up. Any ideas or thought would surely be appreciated.
:::-Bill B.
:
:
Edd: I pulled the rectifier tube and ran the set for an hour and a half and the transformer is warm/hot but you wont get burned and it definitely won't sizzle spit. Now I should pull the output tube and check the B+ voltages again and what does that tell me if they go way up or way down? Thanks for the help.
-Bill B.
5/23/2013 6:49:46 PMEdd(106674:106672)
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::::Hello: I just finished my electrical restoration of a Sears 101.825-4 chassis and it seems the power transformer is running way too hot.It gets almost hot enough to sizzle spit on, and is definitely too hot to leave your hand on. I replaced all capacitors including the electrolytics, except for one .05 which is underneath the tuner assembly and I cannot get to it. Also I did not open up any IF cans to replace caps in there. I read 335 VDC off pin 7 on the 7Z4 rectifier. Each side of the power transformer reads 312 VAC to ground and 621 VAC across the outside leads. I get 306 VDC off pin 2 ( the plate ?) of the 7C5 output tube, and 260VDC off pin 3 ( Grid 1 ? ) and .23 volts off pin 6 ( grid 2? ) The AF tube (driver ) reads 60.5 VDC volts on pin 2 ( the plate ) and .68 VDC on the grid. There is a 330 ohm ( measures 410 ohm ) 1 watt resistor from the cathode of the output tube to ground with a 25 mfd electrolytic across it. That resistor gets too hot to touch ! The power resistors R-32 and R-41 2K 5 watt wirewound also get too hot to touch. The 7Z4 rectifier gives off an awful lot of heat, but I'm gonna assume that's normal ? I replaced two tubes...The 7A6 FM discriminator and the 7C7 FM 3rd. IF. The radio plays beautifully on FM and AM with no hum or any wierd noises from the speaker. It does have a tendency to drift just a tad after it warms up. Any ideas or thought would surely be appreciated.
::::-Bill B.
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::
:Edd: I pulled the rectifier tube and ran the set for an hour and a half and the transformer is warm/hot but you wont get burned and it definitely won't sizzle spit. Now I should pull the output tube and check the B+ voltages again and what does that tell me if they go way up or way down? Thanks for the help.
:-Bill B.
:
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::: ::: ::: ::: ::: ::: ::: ::: ::: ::: ::: :::Sir Bill . . . . ::: ::: :::I don’t have that Samuels schematic at hand and initially would only suggest to have all of the tubes installed in the set and only unplug the rectifier tube OUT of the set and see if the power t- former is cool after about an hour run time with it only being subjected to filamental circuitry loading and with NO B+ being created. ::: ::: ::: :::Then PULL the AF output tubes and place the rectifier tube back in. ::: ::: :::Initially, spot check the main B+ again just to see that the minimal power pull / loading of only the tubes present is not skyrocketing the B level at the first main filter electrolytic. ::: ::: :::Then run an hour and see if this test run is still leaving a normal temperature for the power t-former, as was found before. ::: ::: :::If you then move on to full tube installation for a test run and find overheating, the set must have an excess current pull in the AF power stage circuitry, by virtue of that mentioned overheating cathode resistor. ::: ::: ::: :::By this time, I may then have that units schematic and can give you more exacting /further feedback. ::: ::: ::: ::: ::: ::: :::73's de Edd ::: ::: ::: ::: ::: :::Blessed is he who expects no gratitude, for he shall not be disappointed. ::: ::: ::: ::: ::: ::: |
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::::Hello: I just finished my electrical restoration of a Sears 101.825-4 chassis and it seems the power transformer is running way too hot.It gets almost hot enough to sizzle spit on, and is definitely too hot to leave your hand on. I replaced all capacitors including the electrolytics, except for one .05 which is underneath the tuner assembly and I cannot get to it. Also I did not open up any IF cans to replace caps in there. I read 335 VDC off pin 7 on the 7Z4 rectifier. Each side of the power transformer reads 312 VAC to ground and 621 VAC across the outside leads. I get 306 VDC off pin 2 ( the plate ?) of the 7C5 output tube, and 260VDC off pin 3 ( Grid 1 ? ) and .23 volts off pin 6 ( grid 2? ) The AF tube (driver ) reads 60.5 VDC volts on pin 2 ( the plate ) and .68 VDC on the grid. There is a 330 ohm ( measures 410 ohm ) 1 watt resistor from the cathode of the output tube to ground with a 25 mfd electrolytic across it. That resistor gets too hot to touch ! The power resistors R-32 and R-41 2K 5 watt wirewound also get too hot to touch. The 7Z4 rectifier gives off an awful lot of heat, but I'm gonna assume that's normal ? I replaced two tubes...The 7A6 FM discriminator and the 7C7 FM 3rd. IF. The radio plays beautifully on FM and AM with no hum or any wierd noises from the speaker. It does have a tendency to drift just a tad after it warms up. Any ideas or thought would surely be appreciated.
::::-Bill B.
::
::
:Edd: I pulled the rectifier tube and ran the set for an hour and a half and the transformer is warm/hot but you wont get burned and it definitely won't sizzle spit. Now I should pull the output tube and check the B+ voltages again and what does that tell me if they go way up or way down? Thanks for the help.
:-Bill B.
:
Bill:
The AF circuitry and partucularly the AF output tube is the MAIN consumer of current on that set.( I initially t6hought that big ole thang was having TWO push pull output amps . . .. but just one. )
If you would now, measure the cold resistance of the cathode resistor on the 7C5 and then plug in the set andin order to be able to see how hot the set gets.
a soon as the sets filaments warm up a bitp, measure the DC voltage across the cathode resistor and watch to see if it is climbing up . . . . and the set will be heating up the T-former again.
If so confirm if the 7C5 screen voltage is present and not too high, and mainly, that the negative bias voltage on the
7C5 tube 1`st grid is not decreasing and starting towards being a positive value, which would pull current like MAD and heat up the cathode resistor.
Standing by for your findings . . . tomorrow . . . .
73's de Edd
5/23/2013 8:33:14 PMLewis(106676:106674)
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:::::Hello: I just finished my electrical restoration of a Sears 101.825-4 chassis and it seems the power transformer is running way too hot.It gets almost hot enough to sizzle spit on, and is definitely too hot to leave your hand on. I replaced all capacitors including the electrolytics, except for one .05 which is underneath the tuner assembly and I cannot get to it. Also I did not open up any IF cans to replace caps in there. I read 335 VDC off pin 7 on the 7Z4 rectifier. Each side of the power transformer reads 312 VAC to ground and 621 VAC across the outside leads. I get 306 VDC off pin 2 ( the plate ?) of the 7C5 output tube, and 260VDC off pin 3 ( Grid 1 ? ) and .23 volts off pin 6 ( grid 2? ) The AF tube (driver ) reads 60.5 VDC volts on pin 2 ( the plate ) and .68 VDC on the grid. There is a 330 ohm ( measures 410 ohm ) 1 watt resistor from the cathode of the output tube to ground with a 25 mfd electrolytic across it. That resistor gets too hot to touch ! The power resistors R-32 and R-41 2K 5 watt wirewound also get too hot to touch. The 7Z4 rectifier gives off an awful lot of heat, but I'm gonna assume that's normal ? I replaced two tubes...The 7A6 FM discriminator and the 7C7 FM 3rd. IF. The radio plays beautifully on FM and AM with no hum or any wierd noises from the speaker. It does have a tendency to drift just a tad after it warms up. Any ideas or thought would surely be appreciated.
:::::-Bill B.
:::
:::
::Edd: I pulled the rectifier tube and ran the set for an hour and a half and the transformer is warm/hot but you wont get burned and it definitely won't sizzle spit. Now I should pull the output tube and check the B+ voltages again and what does that tell me if they go way up or way down? Thanks for the help.
::-Bill B.
::
:
:
:Bill:
:
:The AF circuitry and partucularly the AF output tube is the MAIN consumer of current on that set.( I initially t6hought that big ole thang was having TWO push pull output amps . . .. but just one. )
:
:If you would now, measure the cold resistance of the cathode resistor on the 7C5 and then plug in the set andin order to be able to see how hot the set gets.
:a soon as the sets filaments warm up a bitp, measure the DC voltage across the cathode resistor and watch to see if it is climbing up . . . . and the set will be heating up the T-former again.
:If so confirm if the 7C5 screen voltage is present and not too high, and mainly, that the negative bias voltage on the
:7C5 tube 1`st grid is not decreasing and starting towards being a positive value, which would pull current like MAD and heat up the cathode resistor.
:Standing by for your findings . . . tomorrow . . . .
:73's de Edd
::::
:::: :::: :::: :::: :::: :::: :::: :::: :::: :::: :::: ::::Sir Bill . . . . :::: :::: ::::I don’t have that Samuels schematic at hand and initially would only suggest to have all of the tubes installed in the set and only unplug the rectifier tube OUT of the set and see if the power t- former is cool after about an hour run time with it only being subjected to filamental circuitry loading and with NO B+ being created. :::: :::: :::: ::::Then PULL the AF output tubes and place the rectifier tube back in. :::: :::: ::::Initially, spot check the main B+ again just to see that the minimal power pull / loading of only the tubes present is not skyrocketing the B level at the first main filter electrolytic. :::: :::: ::::Then run an hour and see if this test run is still leaving a normal temperature for the power t-former, as was found before. :::: :::: ::::If you then move on to full tube installation for a test run and find overheating, the set must have an excess current pull in the AF power stage circuitry, by virtue of that mentioned overheating cathode resistor. :::: :::: :::: ::::By this time, I may then have that units schematic and can give you more exacting /further feedback. :::: :::: :::: :::: :::: :::: ::::73's de Edd :::: :::: :::: :::: :::: ::::Blessed is he who expects no gratitude, for he shall not be disappointed. :::: :::: :::: :::: :::: :::: |
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:::::Hello: I just finished my electrical restoration of a Sears 101.825-4 chassis and it seems the power transformer is running way too hot.It gets almost hot enough to sizzle spit on, and is definitely too hot to leave your hand on. I replaced all capacitors including the electrolytics, except for one .05 which is underneath the tuner assembly and I cannot get to it. Also I did not open up any IF cans to replace caps in there. I read 335 VDC off pin 7 on the 7Z4 rectifier. Each side of the power transformer reads 312 VAC to ground and 621 VAC across the outside leads. I get 306 VDC off pin 2 ( the plate ?) of the 7C5 output tube, and 260VDC off pin 3 ( Grid 1 ? ) and .23 volts off pin 6 ( grid 2? ) The AF tube (driver ) reads 60.5 VDC volts on pin 2 ( the plate ) and .68 VDC on the grid. There is a 330 ohm ( measures 410 ohm ) 1 watt resistor from the cathode of the output tube to ground with a 25 mfd electrolytic across it. That resistor gets too hot to touch ! The power resistors R-32 and R-41 2K 5 watt wirewound also get too hot to touch. The 7Z4 rectifier gives off an awful lot of heat, but I'm gonna assume that's normal ? I replaced two tubes...The 7A6 FM discriminator and the 7C7 FM 3rd. IF. The radio plays beautifully on FM and AM with no hum or any wierd noises from the speaker. It does have a tendency to drift just a tad after it warms up. Any ideas or thought would surely be appreciated.
:::::-Bill B.
:::
:::
::Edd: I pulled the rectifier tube and ran the set for an hour and a half and the transformer is warm/hot but you wont get burned and it definitely won't sizzle spit. Now I should pull the output tube and check the B+ voltages again and what does that tell me if they go way up or way down? Thanks for the help.
::-Bill B.
::
:
:
:Bill:
:
:The AF circuitry and partucularly the AF output tube is the MAIN consumer of current on that set.( I initially t6hought that big ole thang was having TWO push pull output amps . . .. but just one. )
:
:If you would now, measure the cold resistance of the cathode resistor on the 7C5 and then plug in the set andin order to be able to see how hot the set gets.
:a soon as the sets filaments warm up a bitp, measure the DC voltage across the cathode resistor and watch to see if it is climbing up . . . . and the set will be heating up the T-former again.
:If so confirm if the 7C5 screen voltage is present and not too high, and mainly, that the negative bias voltage on the
:7C5 tube 1`st grid is not decreasing and starting towards being a positive value, which would pull current like MAD and heat up the cathode resistor.
:Standing by for your findings . . . tomorrow . . . .
:73's de Edd
Edd didn't really answer your question, IMHO. The output stage is about the only place that enough current is used to overload the power supply, the rest go through dropping resistors. I see that you pulled the rectifier tube, now you have elininated the filament strin for a short that might be heating up your transformer. Now, put in the rectifier tube and pull the ouptup tube(s). If the transformer stays reasonably cool (they will get somewhat warm even with no load, that is the molecules of iron being chased around by the magnetic field that makes the thing work in the first place), you have eliminated the filter caps, the output transformer, speaker field, if there is one, and are now down to the output stage. The transformer will get a little warmer with the rectifier in than it did before, you should still be able to hold your hand on it without getting blisteed. (;?)~ In my broadcast days, holding the power transformers of various equipment that was on all the time was a unoffical check of the station equipment. If the transformer was too hot to hold, there was a filter cap or output tube going bad, maybe.
Lewis
Lewis
Lewis
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5/24/2013 12:48:21 PMBill B.(106685:106676)
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::::::Hello: I just finished my electrical restoration of a Sears 101.825-4 chassis and it seems the power transformer is running way too hot.It gets almost hot enough to sizzle spit on, and is definitely too hot to leave your hand on. I replaced all capacitors including the electrolytics, except for one .05 which is underneath the tuner assembly and I cannot get to it. Also I did not open up any IF cans to replace caps in there. I read 335 VDC off pin 7 on the 7Z4 rectifier. Each side of the power transformer reads 312 VAC to ground and 621 VAC across the outside leads. I get 306 VDC off pin 2 ( the plate ?) of the 7C5 output tube, and 260VDC off pin 3 ( Grid 1 ? ) and .23 volts off pin 6 ( grid 2? ) The AF tube (driver ) reads 60.5 VDC volts on pin 2 ( the plate ) and .68 VDC on the grid. There is a 330 ohm ( measures 410 ohm ) 1 watt resistor from the cathode of the output tube to ground with a 25 mfd electrolytic across it. That resistor gets too hot to touch ! The power resistors R-32 and R-41 2K 5 watt wirewound also get too hot to touch. The 7Z4 rectifier gives off an awful lot of heat, but I'm gonna assume that's normal ? I replaced two tubes...The 7A6 FM discriminator and the 7C7 FM 3rd. IF. The radio plays beautifully on FM and AM with no hum or any wierd noises from the speaker. It does have a tendency to drift just a tad after it warms up. Any ideas or thought would surely be appreciated.
::::::-Bill B.
::::
::::
:::Edd: I pulled the rectifier tube and ran the set for an hour and a half and the transformer is warm/hot but you wont get burned and it definitely won't sizzle spit. Now I should pull the output tube and check the B+ voltages again and what does that tell me if they go way up or way down? Thanks for the help.
:::-Bill B.
:::
::
::
::Bill:
::
::The AF circuitry and partucularly the AF output tube is the MAIN consumer of current on that set.( I initially t6hought that big ole thang was having TWO push pull output amps . . .. but just one. )
::
::If you would now, measure the cold resistance of the cathode resistor on the 7C5 and then plug in the set andin order to be able to see how hot the set gets.
::a soon as the sets filaments warm up a bitp, measure the DC voltage across the cathode resistor and watch to see if it is climbing up . . . . and the set will be heating up the T-former again.
::If so confirm if the 7C5 screen voltage is present and not too high, and mainly, that the negative bias voltage on the
::7C5 tube 1`st grid is not decreasing and starting towards being a positive value, which would pull current like MAD and heat up the cathode resistor.
::Standing by for your findings . . . tomorrow . . . .
::73's de Edd
:
:Edd didn't really answer your question, IMHO. The output stage is about the only place that enough current is used to overload the power supply, the rest go through dropping resistors. I see that you pulled the rectifier tube, now you have elininated the filament strin for a short that might be heating up your transformer. Now, put in the rectifier tube and pull the ouptup tube(s). If the transformer stays reasonably cool (they will get somewhat warm even with no load, that is the molecules of iron being chased around by the magnetic field that makes the thing work in the first place), you have eliminated the filter caps, the output transformer, speaker field, if there is one, and are now down to the output stage. The transformer will get a little warmer with the rectifier in than it did before, you should still be able to hold your hand on it without getting blisteed. (;?)~ In my broadcast days, holding the power transformers of various equipment that was on all the time was a unoffical check of the station equipment. If the transformer was too hot to hold, there was a filter cap or output tube going bad, maybe.
:Lewis
:Lewis
:Lewis
:::::
::::: ::::: ::::: ::::: ::::: ::::: ::::: ::::: ::::: ::::: ::::: :::::Sir Bill . . . . ::::: ::::: :::::I don’t have that Samuels schematic at hand and initially would only suggest to have all of the tubes installed in the set and only unplug the rectifier tube OUT of the set and see if the power t- former is cool after about an hour run time with it only being subjected to filamental circuitry loading and with NO B+ being created. ::::: ::::: ::::: :::::Then PULL the AF output tubes and place the rectifier tube back in. ::::: ::::: :::::Initially, spot check the main B+ again just to see that the minimal power pull / loading of only the tubes present is not skyrocketing the B level at the first main filter electrolytic. ::::: ::::: :::::Then run an hour and see if this test run is still leaving a normal temperature for the power t-former, as was found before. ::::: ::::: :::::If you then move on to full tube installation for a test run and find overheating, the set must have an excess current pull in the AF power stage circuitry, by virtue of that mentioned overheating cathode resistor. ::::: ::::: ::::: :::::By this time, I may then have that units schematic and can give you more exacting /further feedback. ::::: ::::: ::::: ::::: ::::: ::::: :::::73's de Edd ::::: ::::: ::::: ::::: ::::: :::::Blessed is he who expects no gratitude, for he shall not be disappointed. ::::: ::::: ::::: ::::: ::::: ::::: |
:::::
:::::
:::::
:::::
:::::
:::::
::::::Hello: I just finished my electrical restoration of a Sears 101.825-4 chassis and it seems the power transformer is running way too hot.It gets almost hot enough to sizzle spit on, and is definitely too hot to leave your hand on. I replaced all capacitors including the electrolytics, except for one .05 which is underneath the tuner assembly and I cannot get to it. Also I did not open up any IF cans to replace caps in there. I read 335 VDC off pin 7 on the 7Z4 rectifier. Each side of the power transformer reads 312 VAC to ground and 621 VAC across the outside leads. I get 306 VDC off pin 2 ( the plate ?) of the 7C5 output tube, and 260VDC off pin 3 ( Grid 1 ? ) and .23 volts off pin 6 ( grid 2? ) The AF tube (driver ) reads 60.5 VDC volts on pin 2 ( the plate ) and .68 VDC on the grid. There is a 330 ohm ( measures 410 ohm ) 1 watt resistor from the cathode of the output tube to ground with a 25 mfd electrolytic across it. That resistor gets too hot to touch ! The power resistors R-32 and R-41 2K 5 watt wirewound also get too hot to touch. The 7Z4 rectifier gives off an awful lot of heat, but I'm gonna assume that's normal ? I replaced two tubes...The 7A6 FM discriminator and the 7C7 FM 3rd. IF. The radio plays beautifully on FM and AM with no hum or any wierd noises from the speaker. It does have a tendency to drift just a tad after it warms up. Any ideas or thought would surely be appreciated.
::::::-Bill B.
::::
::::
:::Edd: I pulled the rectifier tube and ran the set for an hour and a half and the transformer is warm/hot but you wont get burned and it definitely won't sizzle spit. Now I should pull the output tube and check the B+ voltages again and what does that tell me if they go way up or way down? Thanks for the help.
:::-Bill B.
:::
::
::
::Bill:
::
::The AF circuitry and partucularly the AF output tube is the MAIN consumer of current on that set.( I initially t6hought that big ole thang was having TWO push pull output amps . . .. but just one. )
::
::If you would now, measure the cold resistance of the cathode resistor on the 7C5 and then plug in the set andin order to be able to see how hot the set gets.
::a soon as the sets filaments warm up a bitp, measure the DC voltage across the cathode resistor and watch to see if it is climbing up . . . . and the set will be heating up the T-former again.
::If so confirm if the 7C5 screen voltage is present and not too high, and mainly, that the negative bias voltage on the
::7C5 tube 1`st grid is not decreasing and starting towards being a positive value, which would pull current like MAD and heat up the cathode resistor.
::Standing by for your findings . . . tomorrow . . . .
::73's de Edd
:
:Edd didn't really answer your question, IMHO. The output stage is about the only place that enough current is used to overload the power supply, the rest go through dropping resistors. I see that you pulled the rectifier tube, now you have elininated the filament strin for a short that might be heating up your transformer. Now, put in the rectifier tube and pull the ouptup tube(s). If the transformer stays reasonably cool (they will get somewhat warm even with no load, that is the molecules of iron being chased around by the magnetic field that makes the thing work in the first place), you have eliminated the filter caps, the output transformer, speaker field, if there is one, and are now down to the output stage. The transformer will get a little warmer with the rectifier in than it did before, you should still be able to hold your hand on it without getting blisteed. (;?)~ In my broadcast days, holding the power transformers of various equipment that was on all the time was a unoffical check of the station equipment. If the transformer was too hot to hold, there was a filter cap or output tube going bad, maybe.
:Lewis
:Lewis
:Lewis
Lewis: Thanks for the input and I did do those tests...Without the output tubes in place the transformer got barely warm...And an hour without the rectifier tube it got warm/ hot but you could hold onto it without getting burned.
-Bill
5/24/2013 12:44:29 PMBill B.(106684:106674)
::::
::::
::::
::::
::::
::::
::::
::::
:::::Hello: I just finished my electrical restoration of a Sears 101.825-4 chassis and it seems the power transformer is running way too hot.It gets almost hot enough to sizzle spit on, and is definitely too hot to leave your hand on. I replaced all capacitors including the electrolytics, except for one .05 which is underneath the tuner assembly and I cannot get to it. Also I did not open up any IF cans to replace caps in there. I read 335 VDC off pin 7 on the 7Z4 rectifier. Each side of the power transformer reads 312 VAC to ground and 621 VAC across the outside leads. I get 306 VDC off pin 2 ( the plate ?) of the 7C5 output tube, and 260VDC off pin 3 ( Grid 1 ? ) and .23 volts off pin 6 ( grid 2? ) The AF tube (driver ) reads 60.5 VDC volts on pin 2 ( the plate ) and .68 VDC on the grid. There is a 330 ohm ( measures 410 ohm ) 1 watt resistor from the cathode of the output tube to ground with a 25 mfd electrolytic across it. That resistor gets too hot to touch ! The power resistors R-32 and R-41 2K 5 watt wirewound also get too hot to touch. The 7Z4 rectifier gives off an awful lot of heat, but I'm gonna assume that's normal ? I replaced two tubes...The 7A6 FM discriminator and the 7C7 FM 3rd. IF. The radio plays beautifully on FM and AM with no hum or any wierd noises from the speaker. It does have a tendency to drift just a tad after it warms up. Any ideas or thought would surely be appreciated.
:::::-Bill B.
:::
:::
::Edd: I pulled the rectifier tube and ran the set for an hour and a half and the transformer is warm/hot but you wont get burned and it definitely won't sizzle spit. Now I should pull the output tube and check the B+ voltages again and what does that tell me if they go way up or way down? Thanks for the help.
::-Bill B.
::
:
:
:Bill:
:
:The AF circuitry and partucularly the AF output tube is the MAIN consumer of current on that set.( I initially t6hought that big ole thang was having TWO push pull output amps . . .. but just one. )
:
:If you would now, measure the cold resistance of the cathode resistor on the 7C5 and then plug in the set andin order to be able to see how hot the set gets.
:a soon as the sets filaments warm up a bitp, measure the DC voltage across the cathode resistor and watch to see if it is climbing up . . . . and the set will be heating up the T-former again.
:If so confirm if the 7C5 screen voltage is present and not too high, and mainly, that the negative bias voltage on the
:7C5 tube 1`st grid is not decreasing and starting towards being a positive value, which would pull current like MAD and heat up the cathode resistor.
:Standing by for your findings . . . tomorrow . . . .
:73's de Edd
::::
:::: :::: :::: :::: :::: :::: :::: :::: :::: :::: :::: ::::Sir Bill . . . . :::: :::: ::::I don’t have that Samuels schematic at hand and initially would only suggest to have all of the tubes installed in the set and only unplug the rectifier tube OUT of the set and see if the power t- former is cool after about an hour run time with it only being subjected to filamental circuitry loading and with NO B+ being created. :::: :::: :::: ::::Then PULL the AF output tubes and place the rectifier tube back in. :::: :::: ::::Initially, spot check the main B+ again just to see that the minimal power pull / loading of only the tubes present is not skyrocketing the B level at the first main filter electrolytic. :::: :::: ::::Then run an hour and see if this test run is still leaving a normal temperature for the power t-former, as was found before. :::: :::: ::::If you then move on to full tube installation for a test run and find overheating, the set must have an excess current pull in the AF power stage circuitry, by virtue of that mentioned overheating cathode resistor. :::: :::: :::: ::::By this time, I may then have that units schematic and can give you more exacting /further feedback. :::: :::: :::: :::: :::: :::: ::::73's de Edd :::: :::: :::: :::: :::: ::::Blessed is he who expects no gratitude, for he shall not be disappointed. :::: :::: :::: :::: :::: :::: |
::::
::::
::::
::::
::::
::::
:::::Hello: I just finished my electrical restoration of a Sears 101.825-4 chassis and it seems the power transformer is running way too hot.It gets almost hot enough to sizzle spit on, and is definitely too hot to leave your hand on. I replaced all capacitors including the electrolytics, except for one .05 which is underneath the tuner assembly and I cannot get to it. Also I did not open up any IF cans to replace caps in there. I read 335 VDC off pin 7 on the 7Z4 rectifier. Each side of the power transformer reads 312 VAC to ground and 621 VAC across the outside leads. I get 306 VDC off pin 2 ( the plate ?) of the 7C5 output tube, and 260VDC off pin 3 ( Grid 1 ? ) and .23 volts off pin 6 ( grid 2? ) The AF tube (driver ) reads 60.5 VDC volts on pin 2 ( the plate ) and .68 VDC on the grid. There is a 330 ohm ( measures 410 ohm ) 1 watt resistor from the cathode of the output tube to ground with a 25 mfd electrolytic across it. That resistor gets too hot to touch ! The power resistors R-32 and R-41 2K 5 watt wirewound also get too hot to touch. The 7Z4 rectifier gives off an awful lot of heat, but I'm gonna assume that's normal ? I replaced two tubes...The 7A6 FM discriminator and the 7C7 FM 3rd. IF. The radio plays beautifully on FM and AM with no hum or any wierd noises from the speaker. It does have a tendency to drift just a tad after it warms up. Any ideas or thought would surely be appreciated.
:::::-Bill B.
:::
:::
::Edd: I pulled the rectifier tube and ran the set for an hour and a half and the transformer is warm/hot but you wont get burned and it definitely won't sizzle spit. Now I should pull the output tube and check the B+ voltages again and what does that tell me if they go way up or way down? Thanks for the help.
::-Bill B.
::
:
:
:Bill:
:
:The AF circuitry and partucularly the AF output tube is the MAIN consumer of current on that set.( I initially t6hought that big ole thang was having TWO push pull output amps . . .. but just one. )
:
:If you would now, measure the cold resistance of the cathode resistor on the 7C5 and then plug in the set andin order to be able to see how hot the set gets.
:a soon as the sets filaments warm up a bitp, measure the DC voltage across the cathode resistor and watch to see if it is climbing up . . . . and the set will be heating up the T-former again.
:If so confirm if the 7C5 screen voltage is present and not too high, and mainly, that the negative bias voltage on the
:7C5 tube 1`st grid is not decreasing and starting towards being a positive value, which would pull current like MAD and heat up the cathode resistor.
:Standing by for your findings . . . tomorrow . . . .
:73's de Edd
Edd: The cathode resistor measures 440 ohms...on the schematic it says 330 ohms....It gets hot right away. On the plate I read 309 volts after warm up...and 261 volts on G2 and on G1 it is .085 on start up and reads .120 after 15 minutes...G3 and cathode are tied together internally and I measure 16.10 volts. After 15 minutes the transformer is barely warm...It usually takes an hour before you can't touch it ! Someone on another Forum said he had experience with sears radios not likeing line voltages over 117 volts, causing the transformers to heat up. My line voltage is 120-121. He sugested a bucking transformer to lower line voltage....I am not familiar with that at all. Thanks for your time and help.
-Bill B.
6/5/2013 7:59:22 PMBill B.(106845:106684)
:::::
:::::
:::::
:::::
:::::
:::::
:::::
:::::
::::::Hello: I just finished my electrical restoration of a Sears 101.825-4 chassis and it seems the power transformer is running way too hot.It gets almost hot enough to sizzle spit on, and is definitely too hot to leave your hand on. I replaced all capacitors including the electrolytics, except for one .05 which is underneath the tuner assembly and I cannot get to it. Also I did not open up any IF cans to replace caps in there. I read 335 VDC off pin 7 on the 7Z4 rectifier. Each side of the power transformer reads 312 VAC to ground and 621 VAC across the outside leads. I get 306 VDC off pin 2 ( the plate ?) of the 7C5 output tube, and 260VDC off pin 3 ( Grid 1 ? ) and .23 volts off pin 6 ( grid 2? ) The AF tube (driver ) reads 60.5 VDC volts on pin 2 ( the plate ) and .68 VDC on the grid. There is a 330 ohm ( measures 410 ohm ) 1 watt resistor from the cathode of the output tube to ground with a 25 mfd electrolytic across it. That resistor gets too hot to touch ! The power resistors R-32 and R-41 2K 5 watt wirewound also get too hot to touch. The 7Z4 rectifier gives off an awful lot of heat, but I'm gonna assume that's normal ? I replaced two tubes...The 7A6 FM discriminator and the 7C7 FM 3rd. IF. The radio plays beautifully on FM and AM with no hum or any wierd noises from the speaker. It does have a tendency to drift just a tad after it warms up. Any ideas or thought would surely be appreciated.
::::::-Bill B.
::::
::::
:::Edd: I pulled the rectifier tube and ran the set for an hour and a half and the transformer is warm/hot but you wont get burned and it definitely won't sizzle spit. Now I should pull the output tube and check the B+ voltages again and what does that tell me if they go way up or way down? Thanks for the help.
:::-Bill B.
:::
::
::
::Bill:
::
::The AF circuitry and partucularly the AF output tube is the MAIN consumer of current on that set.( I initially t6hought that big ole thang was having TWO push pull output amps . . .. but just one. )
::
::If you would now, measure the cold resistance of the cathode resistor on the 7C5 and then plug in the set andin order to be able to see how hot the set gets.
::a soon as the sets filaments warm up a bitp, measure the DC voltage across the cathode resistor and watch to see if it is climbing up . . . . and the set will be heating up the T-former again.
::If so confirm if the 7C5 screen voltage is present and not too high, and mainly, that the negative bias voltage on the
::7C5 tube 1`st grid is not decreasing and starting towards being a positive value, which would pull current like MAD and heat up the cathode resistor.
::Standing by for your findings . . . tomorrow . . . .
::73's de Edd
:
:
:Edd: The cathode resistor measures 440 ohms...on the schematic it says 330 ohms....It gets hot right away. On the plate I read 309 volts after warm up...and 261 volts on G2 and on G1 it is .085 on start up and reads .120 after 15 minutes...G3 and cathode are tied together internally and I measure 16.10 volts. After 15 minutes the transformer is barely warm...It usually takes an hour before you can't touch it ! Someone on another Forum said he had experience with sears radios not likeing line voltages over 117 volts, causing the transformers to heat up. My line voltage is 120-121. He sugested a bucking transformer to lower line voltage....I am not familiar with that at all. Thanks for your time and help.
:-Bill B.
:
Here's a new note. I tried the bucking transformer which knocked the line voltage down to 108 VAC.... That 440 ohm cathode resistor no longer gets hot and the transformer can be handled without getting a burn. So I think I'll call it good and get to work on the cabinet. Thanks for the help.
-Bill B.
:::::
::::: ::::: ::::: ::::: ::::: ::::: ::::: ::::: ::::: ::::: ::::: :::::Sir Bill . . . . ::::: ::::: :::::I don’t have that Samuels schematic at hand and initially would only suggest to have all of the tubes installed in the set and only unplug the rectifier tube OUT of the set and see if the power t- former is cool after about an hour run time with it only being subjected to filamental circuitry loading and with NO B+ being created. ::::: ::::: ::::: :::::Then PULL the AF output tubes and place the rectifier tube back in. ::::: ::::: :::::Initially, spot check the main B+ again just to see that the minimal power pull / loading of only the tubes present is not skyrocketing the B level at the first main filter electrolytic. ::::: ::::: :::::Then run an hour and see if this test run is still leaving a normal temperature for the power t-former, as was found before. ::::: ::::: :::::If you then move on to full tube installation for a test run and find overheating, the set must have an excess current pull in the AF power stage circuitry, by virtue of that mentioned overheating cathode resistor. ::::: ::::: ::::: :::::By this time, I may then have that units schematic and can give you more exacting /further feedback. ::::: ::::: ::::: ::::: ::::: ::::: :::::73's de Edd ::::: ::::: ::::: ::::: ::::: :::::Blessed is he who expects no gratitude, for he shall not be disappointed. ::::: ::::: ::::: ::::: ::::: ::::: |
:::::
:::::
:::::
:::::
:::::
:::::
::::::Hello: I just finished my electrical restoration of a Sears 101.825-4 chassis and it seems the power transformer is running way too hot.It gets almost hot enough to sizzle spit on, and is definitely too hot to leave your hand on. I replaced all capacitors including the electrolytics, except for one .05 which is underneath the tuner assembly and I cannot get to it. Also I did not open up any IF cans to replace caps in there. I read 335 VDC off pin 7 on the 7Z4 rectifier. Each side of the power transformer reads 312 VAC to ground and 621 VAC across the outside leads. I get 306 VDC off pin 2 ( the plate ?) of the 7C5 output tube, and 260VDC off pin 3 ( Grid 1 ? ) and .23 volts off pin 6 ( grid 2? ) The AF tube (driver ) reads 60.5 VDC volts on pin 2 ( the plate ) and .68 VDC on the grid. There is a 330 ohm ( measures 410 ohm ) 1 watt resistor from the cathode of the output tube to ground with a 25 mfd electrolytic across it. That resistor gets too hot to touch ! The power resistors R-32 and R-41 2K 5 watt wirewound also get too hot to touch. The 7Z4 rectifier gives off an awful lot of heat, but I'm gonna assume that's normal ? I replaced two tubes...The 7A6 FM discriminator and the 7C7 FM 3rd. IF. The radio plays beautifully on FM and AM with no hum or any wierd noises from the speaker. It does have a tendency to drift just a tad after it warms up. Any ideas or thought would surely be appreciated.
::::::-Bill B.
::::
::::
:::Edd: I pulled the rectifier tube and ran the set for an hour and a half and the transformer is warm/hot but you wont get burned and it definitely won't sizzle spit. Now I should pull the output tube and check the B+ voltages again and what does that tell me if they go way up or way down? Thanks for the help.
:::-Bill B.
:::
::
::
::Bill:
::
::The AF circuitry and partucularly the AF output tube is the MAIN consumer of current on that set.( I initially t6hought that big ole thang was having TWO push pull output amps . . .. but just one. )
::
::If you would now, measure the cold resistance of the cathode resistor on the 7C5 and then plug in the set andin order to be able to see how hot the set gets.
::a soon as the sets filaments warm up a bitp, measure the DC voltage across the cathode resistor and watch to see if it is climbing up . . . . and the set will be heating up the T-former again.
::If so confirm if the 7C5 screen voltage is present and not too high, and mainly, that the negative bias voltage on the
::7C5 tube 1`st grid is not decreasing and starting towards being a positive value, which would pull current like MAD and heat up the cathode resistor.
::Standing by for your findings . . . tomorrow . . . .
::73's de Edd
:
:
:Edd: The cathode resistor measures 440 ohms...on the schematic it says 330 ohms....It gets hot right away. On the plate I read 309 volts after warm up...and 261 volts on G2 and on G1 it is .085 on start up and reads .120 after 15 minutes...G3 and cathode are tied together internally and I measure 16.10 volts. After 15 minutes the transformer is barely warm...It usually takes an hour before you can't touch it ! Someone on another Forum said he had experience with sears radios not likeing line voltages over 117 volts, causing the transformers to heat up. My line voltage is 120-121. He sugested a bucking transformer to lower line voltage....I am not familiar with that at all. Thanks for your time and help.
:-Bill B.
:
Here's a new note. I tried the bucking transformer which knocked the line voltage down to 108 VAC.... That 440 ohm cathode resistor no longer gets hot and the transformer can be handled without getting a burn. So I think I'll call it good and get to work on the cabinet. Thanks for the help.
-Bill B.
6/6/2013 7:15:14 AMLewis(106854:106845)
::::::
::::::
::::::
::::::
::::::
::::::
::::::
::::::
:::::::Hello: I just finished my electrical restoration of a Sears 101.825-4 chassis and it seems the power transformer is running way too hot.It gets almost hot enough to sizzle spit on, and is definitely too hot to leave your hand on. I replaced all capacitors including the electrolytics, except for one .05 which is underneath the tuner assembly and I cannot get to it. Also I did not open up any IF cans to replace caps in there. I read 335 VDC off pin 7 on the 7Z4 rectifier. Each side of the power transformer reads 312 VAC to ground and 621 VAC across the outside leads. I get 306 VDC off pin 2 ( the plate ?) of the 7C5 output tube, and 260VDC off pin 3 ( Grid 1 ? ) and .23 volts off pin 6 ( grid 2? ) The AF tube (driver ) reads 60.5 VDC volts on pin 2 ( the plate ) and .68 VDC on the grid. There is a 330 ohm ( measures 410 ohm ) 1 watt resistor from the cathode of the output tube to ground with a 25 mfd electrolytic across it. That resistor gets too hot to touch ! The power resistors R-32 and R-41 2K 5 watt wirewound also get too hot to touch. The 7Z4 rectifier gives off an awful lot of heat, but I'm gonna assume that's normal ? I replaced two tubes...The 7A6 FM discriminator and the 7C7 FM 3rd. IF. The radio plays beautifully on FM and AM with no hum or any wierd noises from the speaker. It does have a tendency to drift just a tad after it warms up. Any ideas or thought would surely be appreciated.
:::::::-Bill B.
:::::
:::::
::::Edd: I pulled the rectifier tube and ran the set for an hour and a half and the transformer is warm/hot but you wont get burned and it definitely won't sizzle spit. Now I should pull the output tube and check the B+ voltages again and what does that tell me if they go way up or way down? Thanks for the help.
::::-Bill B.
::::
:::
:::
:::Bill:
:::
:::The AF circuitry and partucularly the AF output tube is the MAIN consumer of current on that set.( I initially t6hought that big ole thang was having TWO push pull output amps . . .. but just one. )
:::
:::If you would now, measure the cold resistance of the cathode resistor on the 7C5 and then plug in the set andin order to be able to see how hot the set gets.
:::a soon as the sets filaments warm up a bitp, measure the DC voltage across the cathode resistor and watch to see if it is climbing up . . . . and the set will be heating up the T-former again.
:::If so confirm if the 7C5 screen voltage is present and not too high, and mainly, that the negative bias voltage on the
:::7C5 tube 1`st grid is not decreasing and starting towards being a positive value, which would pull current like MAD and heat up the cathode resistor.
:::Standing by for your findings . . . tomorrow . . . .
:::73's de Edd
::
::
::Edd: The cathode resistor measures 440 ohms...on the schematic it says 330 ohms....It gets hot right away. On the plate I read 309 volts after warm up...and 261 volts on G2 and on G1 it is .085 on start up and reads .120 after 15 minutes...G3 and cathode are tied together internally and I measure 16.10 volts. After 15 minutes the transformer is barely warm...It usually takes an hour before you can't touch it ! Someone on another Forum said he had experience with sears radios not likeing line voltages over 117 volts, causing the transformers to heat up. My line voltage is 120-121. He sugested a bucking transformer to lower line voltage....I am not familiar with that at all. Thanks for your time and help.
::-Bill B.
::
: Here's a new note. I tried the bucking transformer which knocked the line voltage down to 108 VAC.... That 440 ohm cathode resistor no longer gets hot and the transformer can be handled without getting a burn. So I think I'll call it good and get to work on the cabinet. Thanks for the help.
:-Bill B.
::::::
:::::: :::::: :::::: :::::: :::::: :::::: :::::: :::::: :::::: :::::: :::::: ::::::Sir Bill . . . . :::::: :::::: ::::::I don’t have that Samuels schematic at hand and initially would only suggest to have all of the tubes installed in the set and only unplug the rectifier tube OUT of the set and see if the power t- former is cool after about an hour run time with it only being subjected to filamental circuitry loading and with NO B+ being created. :::::: :::::: :::::: ::::::Then PULL the AF output tubes and place the rectifier tube back in. :::::: :::::: ::::::Initially, spot check the main B+ again just to see that the minimal power pull / loading of only the tubes present is not skyrocketing the B level at the first main filter electrolytic. :::::: :::::: ::::::Then run an hour and see if this test run is still leaving a normal temperature for the power t-former, as was found before. :::::: :::::: ::::::If you then move on to full tube installation for a test run and find overheating, the set must have an excess current pull in the AF power stage circuitry, by virtue of that mentioned overheating cathode resistor. :::::: :::::: :::::: ::::::By this time, I may then have that units schematic and can give you more exacting /further feedback. :::::: :::::: :::::: :::::: :::::: :::::: ::::::73's de Edd :::::: :::::: :::::: :::::: :::::: ::::::Blessed is he who expects no gratitude, for he shall not be disappointed. :::::: :::::: :::::: :::::: :::::: :::::: |
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:::::::Hello: I just finished my electrical restoration of a Sears 101.825-4 chassis and it seems the power transformer is running way too hot.It gets almost hot enough to sizzle spit on, and is definitely too hot to leave your hand on. I replaced all capacitors including the electrolytics, except for one .05 which is underneath the tuner assembly and I cannot get to it. Also I did not open up any IF cans to replace caps in there. I read 335 VDC off pin 7 on the 7Z4 rectifier. Each side of the power transformer reads 312 VAC to ground and 621 VAC across the outside leads. I get 306 VDC off pin 2 ( the plate ?) of the 7C5 output tube, and 260VDC off pin 3 ( Grid 1 ? ) and .23 volts off pin 6 ( grid 2? ) The AF tube (driver ) reads 60.5 VDC volts on pin 2 ( the plate ) and .68 VDC on the grid. There is a 330 ohm ( measures 410 ohm ) 1 watt resistor from the cathode of the output tube to ground with a 25 mfd electrolytic across it. That resistor gets too hot to touch ! The power resistors R-32 and R-41 2K 5 watt wirewound also get too hot to touch. The 7Z4 rectifier gives off an awful lot of heat, but I'm gonna assume that's normal ? I replaced two tubes...The 7A6 FM discriminator and the 7C7 FM 3rd. IF. The radio plays beautifully on FM and AM with no hum or any wierd noises from the speaker. It does have a tendency to drift just a tad after it warms up. Any ideas or thought would surely be appreciated.
:::::::-Bill B.
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::::Edd: I pulled the rectifier tube and ran the set for an hour and a half and the transformer is warm/hot but you wont get burned and it definitely won't sizzle spit. Now I should pull the output tube and check the B+ voltages again and what does that tell me if they go way up or way down? Thanks for the help.
::::-Bill B.
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:::Bill:
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:::The AF circuitry and partucularly the AF output tube is the MAIN consumer of current on that set.( I initially t6hought that big ole thang was having TWO push pull output amps . . .. but just one. )
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:::If you would now, measure the cold resistance of the cathode resistor on the 7C5 and then plug in the set andin order to be able to see how hot the set gets.
:::a soon as the sets filaments warm up a bitp, measure the DC voltage across the cathode resistor and watch to see if it is climbing up . . . . and the set will be heating up the T-former again.
:::If so confirm if the 7C5 screen voltage is present and not too high, and mainly, that the negative bias voltage on the
:::7C5 tube 1`st grid is not decreasing and starting towards being a positive value, which would pull current like MAD and heat up the cathode resistor.
:::Standing by for your findings . . . tomorrow . . . .
:::73's de Edd
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::Edd: The cathode resistor measures 440 ohms...on the schematic it says 330 ohms....It gets hot right away. On the plate I read 309 volts after warm up...and 261 volts on G2 and on G1 it is .085 on start up and reads .120 after 15 minutes...G3 and cathode are tied together internally and I measure 16.10 volts. After 15 minutes the transformer is barely warm...It usually takes an hour before you can't touch it ! Someone on another Forum said he had experience with sears radios not likeing line voltages over 117 volts, causing the transformers to heat up. My line voltage is 120-121. He sugested a bucking transformer to lower line voltage....I am not familiar with that at all. Thanks for your time and help.
::-Bill B.
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: Here's a new note. I tried the bucking transformer which knocked the line voltage down to 108 VAC.... That 440 ohm cathode resistor no longer gets hot and the transformer can be handled without getting a burn. So I think I'll call it good and get to work on the cabinet. Thanks for the help.
:-Bill B.
Bill:
You might want to put a dropping resistor in the line cord, but be careful as it will be hot both physically and electrically, so you will have to be careful that it can dissipate heat and be away from fingers.
Lewis
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