Montgomery Ward Airline 15BR-1547A No Radio Reception and pesistant HUM

1/1/2008 1:23:49 PMTony Cooprider

Hello,

I'm a relatively new radio hobbyist, having completed 3 restorations. I'm presently working on a Airline 15BR-1547A Airline (tabletop). The bakelite cabinet and chassis are super clean. I recapped the radio (all paper and electrolytics) and replaced all tubes with NOS tubes. I replaced the selenium rectifier (just to be safe) with a diode. I also replaced a couple of suspect resistors. This model also has a phonograph input. Upon testing by injecting a 1KHz audio into the phono input, the unit plays and amplifies the phono input. There is however a very bad and persistant 60Hz hum. The problem which is driving me nuts(!!!) is that the unit will not pickup ANY AM stations. The Loop antenna is connected and intact (no opens). It does not make any sounds as I tune across the entire range. The unit just produces hum and some random noise when in the AM mode. Taping with a screwdrive on various places in the circuit produces expected pops. Unfortunately I don't have an isolation transformer and connecting the O-Scope ground to chassis produces some bad side effects (arc welding 101) which I've learned the hardway. Just probing with an ungrounded scope lead I've can see the power supply is a half way rectified and the caps are producing a seemingly usable DC (with some exponential decay ripple). Using a Heathkit signal tracer has been difficult because I just detect 60Hz basically everywhere in the unit. Any thought starters would be greatly appreciated. Frustrated in snowy Rochester Michigan! Thanks,
Tony

1/2/2008 4:31:43 PMJiM mann

Check the grid of the oscillator tube to see if it's running a few volts negative. Your oscillator may not be running. You can also check it by placing the set beside a working second radio tuned to an empty frequency, and tuning the set until you hear it in the second radio as a "dead" or unmodulated carrier signal. It will be obvious. No signal could mean a bad resistor (gone high in value) or a bad tube. Note that some (plenty) of tubes test well enough but will refuse to work in an oscillator circuit.
Jim

1/2/2008 4:37:33 PMRadiodoc

Tony,

One thing you can do is use a .1MFD cap between the O'scope ground clip and radio chassis to isolate the two. Just be sure not to come in contact between the scope clip and chassis of the radio. Measure the voltage on pin 1 (oscillator grid) of the 12BE6 and common B minus with a VOM meter. It should be a few volts negative if the oscillator is operating, perhaps minus 5 to 7 volts.

Radiodoc
**********

:Hello,
:
:I'm a relatively new radio hobbyist, having completed 3 restorations. I'm presently working on a Airline 15BR-1547A Airline (tabletop). The bakelite cabinet and chassis are super clean. I recapped the radio (all paper and electrolytics) and replaced all tubes with NOS tubes. I replaced the selenium rectifier (just to be safe) with a diode. I also replaced a couple of suspect resistors. This model also has a phonograph input. Upon testing by injecting a 1KHz audio into the phono input, the unit plays and amplifies the phono input. There is however a very bad and persistant 60Hz hum. The problem which is driving me nuts(!!!) is that the unit will not pickup ANY AM stations. The Loop antenna is connected and intact (no opens). It does not make any sounds as I tune across the entire range. The unit just produces hum and some random noise when in the AM mode. Taping with a screwdrive on various places in the circuit produces expected pops. Unfortunately I don't have an isolation transformer and connecting the O-Scope ground to chassis produces some bad side effects (arc welding 101) which I've learned the hardway. Just probing with an ungrounded scope lead I've can see the power supply is a half way rectified and the caps are producing a seemingly usable DC (with some exponential decay ripple). Using a Heathkit signal tracer has been difficult because I just detect 60Hz basically everywhere in the unit. Any thought starters would be greatly appreciated. Frustrated in snowy Rochester Michigan! Thanks,
:Tony

1/2/2008 6:15:26 PMPeter G. Balazsy

Before I bought my isolation transformer I welded a scope ground clip too!!!
So I found that I could "float" the scope by using a 3 prong to 2 prong plug adapter.
Also when working on an early AC/DC radio that does not have an isolated (floating) ground ...determine which prong of the non-polarized ac plug is actually connected to directly to the radio chassis. Then mark the plug to always SEE which side is ground. Then plug that ground side into the WIDER plug side of your wall outlet.
These measures will help keep things a bit safer while you await delivery of your life-saving isolation transformer.

1/3/2008 10:06:08 PMTony Cooprider

Thanks to all who responded. I had a chance to look at the voltage on pin 1. Something was definitely wrong. I was measuring line voltage on it (even with plug reversed). It had a very small oscillation on top of the voltage but no DC offset. Basically I got the same reading on my scope on Pin 1 and Pin 2. I think the oscillator coil is bad. This is a 5 terminal device with a primary/secondary and one addtional tap. Any leads on where I could get a replacement for 455kc IF coil? Would be great if I didn't have to go through a serious realignment procedure...but I may be stuck. Thanks for the help.

Tony

:Tony,
:
:One thing you can do is use a .1MFD cap between the O'scope ground clip and radio chassis to isolate the two. Just be sure not to come in contact between the scope clip and chassis of the radio. Measure the voltage on pin 1 (oscillator grid) of the 12BE6 and common B minus with a VOM meter. It should be a few volts negative if the oscillator is operating, perhaps minus 5 to 7 volts.
:
:Radiodoc
:**********
:
:
::Hello,
::
::I'm a relatively new radio hobbyist, having completed 3 restorations. I'm presently working on a Airline 15BR-1547A Airline (tabletop). The bakelite cabinet and chassis are super clean. I recapped the radio (all paper and electrolytics) and replaced all tubes with NOS tubes. I replaced the selenium rectifier (just to be safe) with a diode. I also replaced a couple of suspect resistors. This model also has a phonograph input. Upon testing by injecting a 1KHz audio into the phono input, the unit plays and amplifies the phono input. There is however a very bad and persistant 60Hz hum. The problem which is driving me nuts(!!!) is that the unit will not pickup ANY AM stations. The Loop antenna is connected and intact (no opens). It does not make any sounds as I tune across the entire range. The unit just produces hum and some random noise when in the AM mode. Taping with a screwdrive on various places in the circuit produces expected pops. Unfortunately I don't have an isolation transformer and connecting the O-Scope ground to chassis produces some bad side effects (arc welding 101) which I've learned the hardway. Just probing with an ungrounded scope lead I've can see the power supply is a half way rectified and the caps are producing a seemingly usable DC (with some exponential decay ripple). Using a Heathkit signal tracer has been difficult because I just detect 60Hz basically everywhere in the unit. Any thought starters would be greatly appreciated. Frustrated in snowy Rochester Michigan! Thanks,
::Tony

1/3/2008 11:09:50 PMPeter G. Balazsy

:Thanks to all who responded. I had a chance to look at the voltage on pin 1. Something was definitely wrong. I was measuring line voltage on it (even with plug reversed). It had a very small oscillation on top of the voltage but no DC offset. Basically I got the same reading on my scope on Pin 1 and Pin 2. I think the oscillator coil is bad. This is a 5 terminal device with a primary/secondary and one addtional tap. Any leads on where I could get a replacement for 455kc IF coil? Would be great if I didn't have to go through a serious realignment procedure...but I may be stuck. Thanks for the help.
:
:Tony

You can look at the list of many available old IF xformers at www.oldradioparts.com

1/4/2008 8:35:13 PMTony Cooprider

Does anyone have a way to cross reference Montgomery Ward Airline part numbers to generic part numbers or specification details so a replacement can be selected. Specifically the Osc coil which Riders BOM calls out as a 13D-19064 and the IF coils as 13B-17731 and the Filpec 201-15005.

Thanks Tony

::Thanks to all who responded. I had a chance to look at the voltage on pin 1. Something was definitely wrong. I was measuring line voltage on it (even with plug reversed). It had a very small oscillation on top of the voltage but no DC offset. Basically I got the same reading on my scope on Pin 1 and Pin 2. I think the oscillator coil is bad. This is a 5 terminal device with a primary/secondary and one addtional tap. Any leads on where I could get a replacement for 455kc IF coil? Would be great if I didn't have to go through a serious realignment procedure...but I may be stuck. Thanks for the help.
::
::Tony
:
:You can look at the list of many available old IF xformers at www.oldradioparts.com
:

1/4/2008 9:53:43 PMPeter G. Balazsy

:Does anyone have a way to cross reference Montgomery Ward Airline part numbers to generic part numbers or specification details so a replacement can be selected. Specifically the Osc coil which Riders BOM calls out as a 13D-19064 and the IF coils as 13B-17731 and the Filpec 201-15005.
:
:Thanks Tony
If you carefully peruse the long list there you may find something that makes reference to Airline 455kc etc.
But I would just try to find one that is for YOUR IF freq like 455 or 460 etc.... then just make sure it has the same mounting size and number of wires ...usually 4 ... but some like the second IF can have 5 leads....
But either can be made to work.

1/4/2008 4:50:19 AMTonyJ

Tony:

I have a Philco with a bad oscillator coil and was told that Antique Electronic Supply has a 'universal' coil (70-OSC) that may work in your set. I'm looking into possibly using one in my Philco.