You need to check all the voltages, and particularly trace out the plate supply line. Without B+, no radio will work.
Systematic troubleshooting with your DMM is called for. Don't try for a shot in the dark.
Doug
:I am just about to pull my hair out! I picked up a sweet little 1951 GE 401 with a cream colored bakelite cabinet that is in perfect condition. On preliminary inspection....I got the usual buzz which I thought would be an easy fix with a couple of new filter capacitors or a new 35W4 rectifier tube. Too my dismay I have been working on this thing for 5 hours trying to figure it out. The B+ is almost none existent and it has a loud buzz when it warms up. Any ideas? I tested all the caps and all the resisters....anything odd. Maybe a short in the audio output transformer to ground? Tube socket? Short in one of the coils with the can? Tested all that stuff! No wonder it was only $20. All the tubes tested great!
:Bill: here is the schematic - http://www.nostalgiaair.org/PagesByModel/657/M0007657.pdf
:
:You need to check all the voltages, and particularly trace out the plate supply line. Without B+, no radio will work.
:
:Systematic troubleshooting with your DMM is called for. Don't try for a shot in the dark.
:Doug
:
:
::I am just about to pull my hair out! I picked up a sweet little 1951 GE 401 with a cream colored bakelite cabinet that is in perfect condition. On preliminary inspection....I got the usual buzz which I thought would be an easy fix with a couple of new filter capacitors or a new 35W4 rectifier tube. Too my dismay I have been working on this thing for 5 hours trying to figure it out. The B+ is almost none existent and it has a loud buzz when it warms up. Any ideas? I tested all the caps and all the resisters....anything odd. Maybe a short in the audio output transformer to ground? Tube socket? Short in one of the coils with the can? Tested all that stuff! No wonder it was only $20. All the tubes tested great!
:Doug, Thanks for the advice! A couple of questions....observations....since the B+ starts at the 35W4 what if the DC voltage is virtually non-existent at that point. So I disconnected all contacts to B+ off of the 35W4 and then saw the 110VDC at B+. I hooked back up the B+ to the 50C5 Audio Power output and the B+ was drained down to nothing. Something downstream is causing a draw of all the current. BTW - I had the schematic earlier from this site! It is awesome! Will continue trace until I find what is drawing all the power.
:
:
:
::Bill: here is the schematic - http://www.nostalgiaair.org/PagesByModel/657/M0007657.pdf
::
::You need to check all the voltages, and particularly trace out the plate supply line. Without B+, no radio will work.
::
::Systematic troubleshooting with your DMM is called for. Don't try for a shot in the dark.
::Doug
::
::
:::I am just about to pull my hair out! I picked up a sweet little 1951 GE 401 with a cream colored bakelite cabinet that is in perfect condition. On preliminary inspection....I got the usual buzz which I thought would be an easy fix with a couple of new filter capacitors or a new 35W4 rectifier tube. Too my dismay I have been working on this thing for 5 hours trying to figure it out. The B+ is almost none existent and it has a loud buzz when it warms up. Any ideas? I tested all the caps and all the resisters....anything odd. Maybe a short in the audio output transformer to ground? Tube socket? Short in one of the coils with the can? Tested all that stuff! No wonder it was only $20. All the tubes tested great!
"Qwuerstion". . . . is there a possibility of Cee'fo'ten capacitor being shorted ? ? ? ? Or . . . .remotely. . . a bad C15 B ,
, but probably not, if you still had it in circuit when you shed your loads.
Schema Reference:
73's de Edd
Don't grope for straws - follow a plan.
Doug
:Bill, the usual approach when there is an overload in a circuit, like your B+, is to systematically disconnect portions of the ckt, one at a time, to pinpoint the problem area.
:
:Don't grope for straws - follow a plan.
:Doug
:Doug, That is exactly what I am doing....very good plan. I have isolated it to the 50C5 area...the tube socket is cracked and broken but the tube seems to still fit ok and make contact. I am checking that out as soon as I get home from work.
Also Edd's prior comment sounds plausible. I tested that particular capacitor and it checked out ok...but maybe it is breaking down with a high voltage across it and shorting.....
Nope, I was expecting it to be dead shorted, for your described malady.
Now, hows about having the radio back as it was, and then just solely lifting the input B+ wire of the output transformer and power up and see if your B+ is present.
If , so then reconnect that wire and then lift the plate wire of the output transformer and power up. In that manner we will have isolated the output transformer.
Then, one can proceed in different directions.
:
:
:
::Bill, the usual approach when there is an overload in a circuit, like your B+, is to systematically disconnect portions of the ckt, one at a time, to pinpoint the problem area.
::
::Don't grope for straws - follow a plan.
::Doug
Radiodoc
*************
:
::Doug, That is exactly what I am doing....very good plan. I have isolated it to the 50C5 area...the tube socket is cracked and broken but the tube seems to still fit ok and make contact. I am checking that out as soon as I get home from work.
:
:
:
: Also Edd's prior comment sounds plausible. I tested that particular capacitor and it checked out ok...but maybe it is breaking down with a high voltage across it and shorting.....
:
:
:
:
:Nope, I was expecting it to be dead shorted, for your described malady.
:
:Now, hows about having the radio back as it was, and then just solely lifting the input B+ wire of the output transformer and power up and see if your B+ is present.
:If , so then reconnect that wire and then lift the plate wire of the output transformer and power up. In that manner we will have isolated the output transformer.
:Then, one can proceed in different directions.
:
:
:
::
::
::
:::Bill, the usual approach when there is an overload in a circuit, like your B+, is to systematically disconnect portions of the ckt, one at a time, to pinpoint the problem area.
:::
:::Don't grope for straws - follow a plan.
:::Doug
:
:
:Are we sure the replacement power supply filter capacitors are installed with the correct polarity?
:
:Radiodoc
:*************
:
:
::
:::Doug, That is exactly what I am doing....very good plan. I have isolated it to the 50C5 area...the tube socket is cracked and broken but the tube seems to still fit ok and make contact. I am checking that out as soon as I get home from work.
::
::
::
:: Also Edd's prior comment sounds plausible. I tested that particular capacitor and it checked out ok...but maybe it is breaking down with a high voltage across it and shorting.....
::
::
::
::
::Nope, I was expecting it to be dead shorted, for your described malady.
::
::Now, hows about having the radio back as it was, and then just solely lifting the input B+ wire of the output transformer and power up and see if your B+ is present.
::If , so then reconnect that wire and then lift the plate wire of the output transformer and power up. In that manner we will have isolated the output transformer.
::Then, one can proceed in different directions.
::
::
::
:::
:::
:::
::::Bill, the usual approach when there is an overload in a circuit, like your B+, is to systematically disconnect portions of the ckt, one at a time, to pinpoint the problem area.
::::
::::Don't grope for straws - follow a plan.
::::Doug
::
::
:Nope, I was expecting it to be dead shorted, for your described malady.
:
:Now, hows about having the radio back as it was, and then just solely lifting the input B+ wire of the output transformer and power up and see if your B+ is present.
:If , so then reconnect that wire and then lift the plate wire of the output transformer and power up. In that manner we will have isolated the output transformer.
:Then, one can proceed in different directions.
:
:
:
::
::
::
:::Bill, the usual approach when there is an overload in a circuit, like your B+, is to systematically disconnect portions of the ckt, one at a time, to pinpoint the problem area.
:::
:::Don't grope for straws - follow a plan.
:::Doug
: