Need some direction on this one. I have replaced all the caps, both the dialectric caps, one 50uF, and 30uF, along with testing all the tubs which test good. As soon as it warms up it humms full blast. Turning the volume down does next to nothing. I have taken apart the volume pot and cleaned it. I checked all my connections, good.
NOW, I did some research and it points to the Dial Caps being bad. But they are good. IS this a shorted transformer? Do I have a bad ground on a tub? I noticed someone substituted a tube. The 12AT6 with, if I can remember correctly, a 12AU6 or 12AV6. I looked it up and it was a suitable sub for that tub. SOo..is it a bad resistor? What should I check next? Thank for your help. Joe the lost

Hi Joe

Check connections of your electrolytic caps, 30 & 50 mf. Be sure to use recent manufacturer parts. You can buy 33 & 47 mf @ 160 volts for replacement.

Negative of the caps does not connect to chassis in most radios. Negative will usually end up on pin #2 of your 12AT6 or 12AV6 which are interchangeable.

Norm

:Need some direction on this one. I have replaced all the caps, both the dialectric caps, one 50uF, and 30uF, along with testing all the tubs which test good. As soon as it warms up it humms full blast. Turning the volume down does next to nothing. I have taken apart the volume pot and cleaned it. I checked all my connections, good.
:NOW, I did some research and it points to the Dial Caps being bad. But they are good. IS this a shorted transformer? Do I have a bad ground on a tub? I noticed someone substituted a tube. The 12AT6 with, if I can remember correctly, a 12AU6 or 12AV6. I looked it up and it was a suitable sub for that tub. SOo..is it a bad resistor? What should I check next? Thank for your help. Joe the lost

Thank you for the quick responce. I am fairly confident the elect. caps are on the correct pin and they are new. I will check tonight. Are you saying it has to be something with the caps? No matter what? How about a particular overheated resistor? Just need another logical reason why this humm is getting through. I plan on switching the elect. caps. out again tonight to make triple sure its not the problem. Thanks for your input. Joe the confused.

:Hi Joe
:
: Check connections of your electrolytic caps, 30 & 50 mf. Be sure to use recent manufacturer parts. You can buy 33 & 47 mf @ 160 volts for replacement.
:
: Negative of the caps does not connect to chassis in most radios. Negative will usually end up on pin #2 of your 12AT6 or 12AV6 which are interchangeable.
:
:Norm
:
::Need some direction on this one. I have replaced all the caps, both the dialectric caps, one 50uF, and 30uF, along with testing all the tubs which test good. As soon as it warms up it humms full blast. Turning the volume down does next to nothing. I have taken apart the volume pot and cleaned it. I checked all my connections, good.
::NOW, I did some research and it points to the Dial Caps being bad. But they are good. IS this a shorted transformer? Do I have a bad ground on a tub? I noticed someone substituted a tube. The 12AT6 with, if I can remember correctly, a 12AU6 or 12AV6. I looked it up and it was a suitable sub for that tub. SOo..is it a bad resistor? What should I check next? Thank for your help. Joe the lost

Hi Joe

Loud hum which isn't controlled by the volume control is usually caused by electrolytic caps. Most of the time not connected to the proper place. If reversed they will heat & explode.

A short within a tube can cause hum but this isn't very common. If you have another 12AV6 or 50C5 (maybe 50B5 depends on radio) you can try substitution.

Norm

:Thank you for the quick responce. I am fairly confident the elect. caps are on the correct pin and they are new. I will check tonight. Are you saying it has to be something with the caps? No matter what? How about a particular overheated resistor? Just need another logical reason why this humm is getting through. I plan on switching the elect. caps. out again tonight to make triple sure its not the problem. Thanks for your input. Joe the confused.
:
::Hi Joe
::
:: Check connections of your electrolytic caps, 30 & 50 mf. Be sure to use recent manufacturer parts. You can buy 33 & 47 mf @ 160 volts for replacement.
::
:: Negative of the caps does not connect to chassis in most radios. Negative will usually end up on pin #2 of your 12AT6 or 12AV6 which are interchangeable.
::
::Norm
::
:::Need some direction on this one. I have replaced all the caps, both the dialectric caps, one 50uF, and 30uF, along with testing all the tubs which test good. As soon as it warms up it humms full blast. Turning the volume down does next to nothing. I have taken apart the volume pot and cleaned it. I checked all my connections, good.
:::NOW, I did some research and it points to the Dial Caps being bad. But they are good. IS this a shorted transformer? Do I have a bad ground on a tub? I noticed someone substituted a tube. The 12AT6 with, if I can remember correctly, a 12AU6 or 12AV6. I looked it up and it was a suitable sub for that tub. SOo..is it a bad resistor? What should I check next? Thank for your help. Joe the lost

Do I have a dozie for you! So I recheaked everything I did. How? I usually take a digital picture of the original layout before I do any replacing of the caps just to have a before and after shot. So I copied what was exactly set up in the radio. No doubt. So I tackle the schematic and compare caps with connection points. To make a long story short, be aware of your surroundings. Someone, before me, must of replaced the 1st IF with a slightly different one because it does not match. Plastic coated lines, and two adj screws on top instead of one. The electrolitic caps that I took out and replaced with the 30 & 50mF say they are both 3.3mF. Is that possible? Also, on regular capicitor is not connected in the right place. It goes from the antenna, correct, to another wax covered coil, to ground, when it should go to the heart of the radio the 12BA6 tube. HAVE YOU EVER SEEN ANYTHING LIKE THIS? If so Why? I am going to get some 3.3mF elect. Caps and see what happens. What do you think? Amazing.
:Hi Joe
:
: Loud hum which isn't controlled by the volume control is usually caused by electrolytic caps. Most of the time not connected to the proper place. If reversed they will heat & explode.
:
: A short within a tube can cause hum but this isn't very common. If you have another 12AV6 or 50C5 (maybe 50B5 depends on radio) you can try substitution.
:
:Norm
:
::Thank you for the quick responce. I am fairly confident the elect. caps are on the correct pin and they are new. I will check tonight. Are you saying it has to be something with the caps? No matter what? How about a particular overheated resistor? Just need another logical reason why this humm is getting through. I plan on switching the elect. caps. out again tonight to make triple sure its not the problem. Thanks for your input. Joe the confused.
::
:::Hi Joe
:::
::: Check connections of your electrolytic caps, 30 & 50 mf. Be sure to use recent manufacturer parts. You can buy 33 & 47 mf @ 160 volts for replacement.
:::
::: Negative of the caps does not connect to chassis in most radios. Negative will usually end up on pin #2 of your 12AT6 or 12AV6 which are interchangeable.
:::
:::Norm
:::
::::Need some direction on this one. I have replaced all the caps, both the dialectric caps, one 50uF, and 30uF, along with testing all the tubs which test good. As soon as it warms up it humms full blast. Turning the volume down does next to nothing. I have taken apart the volume pot and cleaned it. I checked all my connections, good.
::::NOW, I did some research and it points to the Dial Caps being bad. But they are good. IS this a shorted transformer? Do I have a bad ground on a tub? I noticed someone substituted a tube. The 12AT6 with, if I can remember correctly, a 12AU6 or 12AV6. I looked it up and it was a suitable sub for that tub. SOo..is it a bad resistor? What should I check next? Thank for your help. Joe the lost

Hi

Use 30 & 50 mf caps. 3.3 mf isn't large enough to filter hum in your radio. Be sure replacement caps were made within the last 30 years. Some of us have old caps around which have gone bad over time, without use.

A different IF Transformer will work as long as frequency rating is similar. Don't know about the coil? Maybe this radio didn't work when someone before you worked on it?

Norm

:Do I have a dozie for you! So I recheaked everything I did. How? I usually take a digital picture of the original layout before I do any replacing of the caps just to have a before and after shot. So I copied what was exactly set up in the radio. No doubt. So I tackle the schematic and compare caps with connection points. To make a long story short, be aware of your surroundings. Someone, before me, must of replaced the 1st IF with a slightly different one because it does not match. Plastic coated lines, and two adj screws on top instead of one. The electrolitic caps that I took out and replaced with the 30 & 50mF say they are both 3.3mF. Is that possible? Also, on regular capicitor is not connected in the right place. It goes from the antenna, correct, to another wax covered coil, to ground, when it should go to the heart of the radio the 12BA6 tube. HAVE YOU EVER SEEN ANYTHING LIKE THIS? If so Why? I am going to get some 3.3mF elect. Caps and see what happens. What do you think? Amazing.
::Hi Joe
::
:: Loud hum which isn't controlled by the volume control is usually caused by electrolytic caps. Most of the time not connected to the proper place. If reversed they will heat & explode.
::
:: A short within a tube can cause hum but this isn't very common. If you have another 12AV6 or 50C5 (maybe 50B5 depends on radio) you can try substitution.
::
::Norm
::
:::Thank you for the quick responce. I am fairly confident the elect. caps are on the correct pin and they are new. I will check tonight. Are you saying it has to be something with the caps? No matter what? How about a particular overheated resistor? Just need another logical reason why this humm is getting through. I plan on switching the elect. caps. out again tonight to make triple sure its not the problem. Thanks for your input. Joe the confused.
:::
::::Hi Joe
::::
:::: Check connections of your electrolytic caps, 30 & 50 mf. Be sure to use recent manufacturer parts. You can buy 33 & 47 mf @ 160 volts for replacement.
::::
:::: Negative of the caps does not connect to chassis in most radios. Negative will usually end up on pin #2 of your 12AT6 or 12AV6 which are interchangeable.
::::
::::Norm
::::
:::::Need some direction on this one. I have replaced all the caps, both the dialectric caps, one 50uF, and 30uF, along with testing all the tubs which test good. As soon as it warms up it humms full blast. Turning the volume down does next to nothing. I have taken apart the volume pot and cleaned it. I checked all my connections, good.
:::::NOW, I did some research and it points to the Dial Caps being bad. But they are good. IS this a shorted transformer? Do I have a bad ground on a tub? I noticed someone substituted a tube. The 12AT6 with, if I can remember correctly, a 12AU6 or 12AV6. I looked it up and it was a suitable sub for that tub. SOo..is it a bad resistor? What should I check next? Thank for your help. Joe the lost

Both of your IF transformers should have two adjusting screws on top. If you look at the schematic, you'll see that both IF transformers have two adjusting condensers. http://www.nostalgiaair.org/PagesByModel/048/M0006048.pdf

Regarding your antenna, that set-up is very common in AC-DC sets, and is common, minus the condenser, in AC sets with loop antennas. The antenna is connected to the small primary loop through a condenser, which keeps the antenna wire from having a direct connection to the chassis (which can be hot if the plug is inserted the wrong way). The other side of the primary loop is connected to the chassis, which is in turn connected to ground through your home's electrical system. Signals alternate back and forth in this primary loop between the antenna and ground (if you happen to connect an antenna to the antenna wire). They are then transferred to the secondary loop by transformer action. The secondary loop is connected to the 12BE6 tube, as it should be. If you decide not to hook any antennas to the antenna primary, then the antenna secondary will be what picks up all of the signals--it will pick up the signals directly, all on its own. Once again, it is connected to the 12BE6 tube, as it should be, and is connected in such a way that everything that needs to happen will happen.

Nothing strange about what you see. Perfectly normal. Study the schematic.

T.

Still working on this radio. I checked all my new caps with a capacitor checker. I also put in a new 12AT6 tube. I have a few questions for someone who really knows there stuff. On the 12AT6 tube I found the 10m ohm resistor, R6, connected to pins 1,2, AND 3. This is not correct according to the schematics. Without it connected to pin 3 though nothing happens when I apply power. why?
Caps C8, C7, and C5 are made out of metal tube. I checked these out with my new capacitor checker and none of these came even close to what they are supposed to be. change these out? THe cap checker worked correctly for all other paper caps.
What voltage should I look for the heater voltages on the daisy chained pins of the tubes?
Finally, what gives? I have practically rebuilt this radio. WHat am I missing? I checked all resistors, tubes, and been over the schematic many times. Is anyone familiar with this radio enough to know a quirk it? It just warms up then goes full volume feedback. I even switched out the volume control. Help,thanks?

:Both of your IF transformers should have two adjusting screws on top. If you look at the schematic, you'll see that both IF transformers have two adjusting condensers. http://www.nostalgiaair.org/PagesByModel/048/M0006048.pdf
:
:Regarding your antenna, that set-up is very common in AC-DC sets, and is common, minus the condenser, in AC sets with loop antennas. The antenna is connected to the small primary loop through a condenser, which keeps the antenna wire from having a direct connection to the chassis (which can be hot if the plug is inserted the wrong way). The other side of the primary loop is connected to the chassis, which is in turn connected to ground through your home's electrical system. Signals alternate back and forth in this primary loop between the antenna and ground (if you happen to connect an antenna to the antenna wire). They are then transferred to the secondary loop by transformer action. The secondary loop is connected to the 12BE6 tube, as it should be. If you decide not to hook any antennas to the antenna primary, then the antenna secondary will be what picks up all of the signals--it will pick up the signals directly, all on its own. Once again, it is connected to the 12BE6 tube, as it should be, and is connected in such a way that everything that needs to happen will happen.
:
:Nothing strange about what you see. Perfectly normal. Study the schematic.
:
:T.

Hi

Pin #1 is grid. Pin #2 is cathode. Pin #3 is filament which could be connected to pin 2. It is reasonable to have a 10 meg grid resistor connected between pin #1 & 2/3.

The first numbers of a tube indicate filament voltage. 12AT6 needs 12 volts. It doesn't have to be exact but around that value. If tubes are lit voltage is usually right. You can read AC filament voltage between pins #3 and #4 on 7 pin tubes.

Paper capacitors get leaky over time. Electrolytics dry out. Tolerance on electrolytic caps can be +80 - -20% so values may not be close. Other circuits may also be having an effect on readings? Important to change electrolytic caps and any paper ones with leakage.

Norm

:Still working on this radio. I checked all my new caps with a capacitor checker. I also put in a new 12AT6 tube. I have a few questions for someone who really knows there stuff. On the 12AT6 tube I found the 10m ohm resistor, R6, connected to pins 1,2, AND 3. This is not correct according to the schematics. Without it connected to pin 3 though nothing happens when I apply power. why?
:Caps C8, C7, and C5 are made out of metal tube. I checked these out with my new capacitor checker and none of these came even close to what they are supposed to be. change these out? THe cap checker worked correctly for all other paper caps.
:What voltage should I look for the heater voltages on the daisy chained pins of the tubes?
:Finally, what gives? I have practically rebuilt this radio. WHat am I missing? I checked all resistors, tubes, and been over the schematic many times. Is anyone familiar with this radio enough to know a quirk it? It just warms up then goes full volume feedback. I even switched out the volume control. Help,thanks?
:
::Both of your IF transformers should have two adjusting screws on top. If you look at the schematic, you'll see that both IF transformers have two adjusting condensers. http://www.nostalgiaair.org/PagesByModel/048/M0006048.pdf
::
::Regarding your antenna, that set-up is very common in AC-DC sets, and is common, minus the condenser, in AC sets with loop antennas. The antenna is connected to the small primary loop through a condenser, which keeps the antenna wire from having a direct connection to the chassis (which can be hot if the plug is inserted the wrong way). The other side of the primary loop is connected to the chassis, which is in turn connected to ground through your home's electrical system. Signals alternate back and forth in this primary loop between the antenna and ground (if you happen to connect an antenna to the antenna wire). They are then transferred to the secondary loop by transformer action. The secondary loop is connected to the 12BE6 tube, as it should be. If you decide not to hook any antennas to the antenna primary, then the antenna secondary will be what picks up all of the signals--it will pick up the signals directly, all on its own. Once again, it is connected to the 12BE6 tube, as it should be, and is connected in such a way that everything that needs to happen will happen.
::
::Nothing strange about what you see. Perfectly normal. Study the schematic.
::
::T.

If pin 2 is connected to pin 3, then pin 3 must be connected to B-. Usually the 12AV6 tube is at the end of the filament string (for hum reasons), and has one of its pins connected to the line cord (which happens to be, and should be B-). If you connect the cathode to pin 4, and pin 3 is the grounded pin, you will get terrible humming because the cathode will have AC heater voltage introduced to it. Make sure that the cathode is connected to the heater pin that's grounded (connected to the line cord...usually through the switch). Or else make sure that the cathode has its own separate wire going to B-.

The reason why the radio won't work without the 10 meg resistor going from the grid (pin 1) to B- (pins 2 and 3) is because this is the grid leak resistor. It leaks off a small amount of the electrons that collect on the grid as they pass by from the cathode. This biases the grid at a proper negative bias. Without the leak, the grid would go much more negative, and would cut off all electron flow from the cathode.

Thomas

It works!! somewhat.... what was wrong? I followed what was there. I have the digital picture to prove that it was done wrong to begin with. I had the positive leads to the elect. caps correct. It took awhile for it to sink in that the neg leads were on the right pin, but wrong tube. Yes, who ever tried to fix this radio connected the wrong sized caps to the wrong tube. Neg leds go to the third pin on the 12AT6 tube not the one next to it, 12BA6. Thank you for all your help. I will make a donation ASAP.
Still have a problem with getting radio stations in though. I adj the IF to make my signal go as load it can go but I can barely get a radio station in. I get in three places on the freq scale a high pitch whinning or whistle. That comes through load and clear but really no radio stations. Anyone think they know why?

Regarding electrolytics, as long as they connect to B- somewhere in the radio, all is good. They can connect to a point that has B- at the 12BA6 or at the 12AV6, or anywhere else that B- connects. It is always best to connect them to a main buss line so that they're not filtering through some B- line that's also connected to audio (this can set up fluctuations in the line on occasion, that will cause hum in the audio). ...But, other than the slight problem I just mentioned, they can connect to any B- point. Just because the schematic has them wired one way doesn't mean that you'll find them this way in the set. The schematic shows how everything is electrically hooked up. It does not show actual physical placement.

Thomas

Thanks for the insite. Maybe the person before had this in mind. I am just glad that the buzz went away. Do you have an idea on the high pitched wistling? I hooked up my signal gen to the antenna and tried to feed in 455kc. I get several spots on the scale where it gets really loud but no radio stations. Tuning issue?
I followed the given schematic tunning instructions, in order. Wondering if there is another problem. Thanks for all your help. Joe
:Regarding electrolytics, as long as they connect to B- somewhere in the radio, all is good. They can connect to a point that has B- at the 12BA6 or at the 12AV6, or anywhere else that B- connects. It is always best to connect them to a main buss line so that they're not filtering through some B- line that's also connected to audio (this can set up fluctuations in the line on occasion, that will cause hum in the audio). ...But, other than the slight problem I just mentioned, they can connect to any B- point. Just because the schematic has them wired one way doesn't mean that you'll find them this way in the set. The schematic shows how everything is electrically hooked up. It does not show actual physical placement.
:
:Thomas

The loop can't be too close to the oscillator, and sometimes it's necessary to shield the oscillator and RF tubes. As long as all components underneath the chassis are in perfect working order, the above actions are pretty much all you can do. However, if the components underneath are bad, you should attend to them, first. Condensers must be perfect. They absolutely cannot have any leakage at all.

Thomas

Just as another point of interest and info on that model radio.
I own this exact model radio... and mine was suffering from the dreaded silver mica disease in both IF cans.

So I think most of these units manufactured at the same time may all start to see this problem by now as the silver in the mica oxidizes and or migrates with time.

I pulled both IF cans and disconnected the integral caps inside the cans and put new ones under the chassis which solved my problem.
.. however THAT kind of noise indicating this problem ....is a loud intermittent static crashing sounds like during a lighting storm.
Keep this all in mind... good luck.

Just wanted to let everyone know that it is now a functional radio. Yaaiee. Thank you everyone for your help. I swapped out a the detector tube, again and I got 810 WGRY . From that I tuned it again for a lowder signal and it just fell all in line. I am glad it did because the case cleaned up so nicely. It looks like a brand new radio. Thank you everyone for your help again. I just think it needed time to burn in. This was a tuffy.

:Just as another point of interest and info on that model radio.
:I own this exact model radio... and mine was suffering from the dreaded silver mica disease in both IF cans.
:
:So I think most of these units manufactured at the same time may all start to see this problem by now as the silver in the mica oxidizes and or migrates with time.
:
:I pulled both IF cans and disconnected the integral caps inside the cans and put new ones under the chassis which solved my problem.
:.. however THAT kind of noise indicating this problem ....is a loud intermittent static crashing sounds like during a lighting storm.
:Keep this all in mind... good luck.
:

Joe, see your answers here: http://antiqueradios.com/forums/viewtopic.php?t=59975

:Need some direction on this one. I have replaced all the caps, both the dialectric caps, one 50uF, and 30uF, along with testing all the tubs which test good. As soon as it warms up it humms full blast. Turning the volume down does next to nothing. I have taken apart the volume pot and cleaned it. I checked all my connections, good.
:NOW, I did some research and it points to the Dial Caps being bad. But they are good. IS this a shorted transformer? Do I have a bad ground on a tub? I noticed someone substituted a tube. The 12AT6 with, if I can remember correctly, a 12AU6 or 12AV6. I looked it up and it was a suitable sub for that tub. SOo..is it a bad resistor? What should I check next? Thank for your help. Joe the lost

Just wanted to let everyone know that it is now a functional radio. Yaaiee. Thank you everyone for your help. I swapped out a the detector tube, again and I got 810 WGRY . From that I tuned it again for a lowder signal and it just fell all in line. I am glad it did because the case cleaned up so nicely. It looks like a brand new radio. Thank you everyone for your help again. I just think it needed time to burn in. This was a tuffy.

:Joe, see your answers here: http://antiqueradios.com/forums/viewtopic.php?t=59975
:
::Need some direction on this one. I have replaced all the caps, both the dialectric caps, one 50uF, and 30uF, along with testing all the tubs which test good. As soon as it warms up it humms full blast. Turning the volume down does next to nothing. I have taken apart the volume pot and cleaned it. I checked all my connections, good.
::NOW, I did some research and it points to the Dial Caps being bad. But they are good. IS this a shorted transformer? Do I have a bad ground on a tub? I noticed someone substituted a tube. The 12AT6 with, if I can remember correctly, a 12AU6 or 12AV6. I looked it up and it was a suitable sub for that tub. SOo..is it a bad resistor? What should I check next? Thank for your help. Joe the lost