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 Post subject: [Solved] Airline 04BR-907A Problems
PostPosted: Nov Tue 21, 2017 10:55 pm 
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Joined: Jul Mon 25, 2016 11:34 am
Posts: 268
Location: Wilton IA
Hi everyone,
I am working on an Airline 04BR-907A radio, and just finished recapping it. I turned it on for the first test, had it turned to radio, and the band knob turned to BC, but could not get anything. I am not getting any sound beside the occasional static in the speaker. All of the tubes do light up, and I am not smelling anything burning.

https://www.radiomuseum.org/r/montgomery_04br907a.html

I am not too great on troubleshooting yet, so could someone help me get in the right direction?

Thanks,
Noah


Last edited by wowsk on Dec Thu 14, 2017 11:03 pm, edited 1 time in total.

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 Post subject: Re: Airline 04BR-907A Problems
PostPosted: Nov Wed 22, 2017 2:23 am 
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Location: Livermore, CA
Hi Noah

Measure voltages on pin #3 of each 6F6 tube. Do you have positive voltage? Plate and screen of each other tube should have a positive voltage. Does the eye tube glow green? If so you have B+ voltage.

http://www.nostalgiaair.org/pagesbymode ... 011000.pdf

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 Post subject: Re: Airline 04BR-907A Problems
PostPosted: Nov Wed 22, 2017 3:20 am 
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Joined: Jul Mon 25, 2016 11:34 am
Posts: 268
Location: Wilton IA
Thanks for the tips Norm!
I will measure the voltages tomorrow, getting late. The eye tube does glow green, it is nice and strong.

Thanks,
Noah


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 Post subject: Re: Airline 04BR-907A Problems
PostPosted: Nov Wed 22, 2017 3:40 am 
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Joined: Nov Mon 06, 2017 7:45 pm
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Location: Sherwood, Oregon
Make sure your selector & band switches are making good contact.


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 Post subject: Re: Airline 04BR-907A Problems
PostPosted: Nov Wed 22, 2017 4:59 pm 
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Joined: Jul Mon 25, 2016 11:34 am
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Location: Wilton IA
I checked all of the voltages on the tubes right now and they were all in the general vicinity of what the schematic gave. Many seemed to be 20 volts lower than given on the schematic.

I will try rechecking just to make sure.

Thanks so much,
Noah


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 Post subject: Re: Airline 04BR-907A Problems
PostPosted: Nov Wed 22, 2017 5:15 pm 
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Joined: Jan Thu 01, 1970 1:00 am
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Location: Silver Spring MD, USA
With the volume up about halfway and the set on, touch a metal screwdriver tip to the center tab of the volume control. Do you hear a loud buzz in the speaker?

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 Post subject: Re: Airline 04BR-907A Problems
PostPosted: Nov Wed 22, 2017 5:55 pm 
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Joined: Jul Mon 25, 2016 11:34 am
Posts: 268
Location: Wilton IA
Yes there is a steady buzz, when I touch a screwdriver tip to the center of the volume control. The loudness of the buzz changes with how far up the volume is.

Does this mean something good or bad?

Thanks,
Noah


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 Post subject: Re: Airline 04BR-907A Problems
PostPosted: Nov Thu 23, 2017 2:06 am 
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Joined: Jan Thu 01, 1970 1:00 am
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Location: Silver Spring MD, USA
It's good. You've divided the radio in half at the volume control and the buzz means the audio section of the set is working.

This most likely means that your problem is in the front end - the part that receives signal and converts it to audio.

Did the set work at all before you recapped it? Did you adjust any of the trimmers after recapping?

EDIT: I realized I should clarify this procedure a bit, I was not clear in what I wrote earlier.

Others will help I am sure, but here is one more easy test at this stage without starting to trace the circuit. Put a working radio near the Airline. Turn the second radio on and tune it to somewhere in the BC band - around 1200-1400 khz. A weak station is ok.

Now with the Airline on, and its volume turned down, tune it from about 455 khz below the frequency the working radio is tuned to. So if you have the second radio at 1200, you should tune the Airline from a bit below 745 to 900 or so. You will hear a tone/squeal from the second radio when you tune the oscillator frequency of the Airline (assuming it is working).

I believe the local oscillator on your set will run 455 khz above the frequency you have the 2nd radio on, hence starting about 745-ish on the Airline. You should hear the tone about 1200 on the second set. The oscillator on the Airline will run at 745 + 455 = 1200. The Airline may not be aligned to exactly 455 khz, and the dial calibration may not be super accurate, so you may need to tune around a bit.

-K

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 Post subject: Re: Airline 04BR-907A Problems
PostPosted: Nov Fri 24, 2017 4:14 pm 
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Joined: Jul Mon 25, 2016 11:34 am
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Location: Wilton IA
HalliFan,
The set did not work at all before I recapped it. I am repairing this for someone else, and I think before I got it they had it on for ten minutes or so every once in a while. I was hoping this would not ruin the transformer, but could this be the problem?

I have not adjusted the trimmers either.

I tried your procedure, but to no avail. I did not get any tone in the second radio when I turned on the Airline. I ran the the dial all the way up and down multiple times, but unless it is hard to hear, I didn't hear any tone.

Thanks for all of the help,
Noah


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 Post subject: Re: Airline 04BR-907A Problems
PostPosted: Nov Fri 24, 2017 7:07 pm 
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Joined: Jan Thu 01, 1970 1:00 am
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Location: Silver Spring MD, USA
wowsk wrote:
HalliFan,
The set did not work at all before I recapped it. I am repairing this for someone else, and I think before I got it they had it on for ten minutes or so every once in a while. I was hoping this would not ruin the transformer, but could this be the problem?

I have not adjusted the trimmers either.

I tried your procedure, but to no avail. I did not get any tone in the second radio when I turned on the Airline. I ran the the dial all the way up and down multiple times, but unless it is hard to hear, I didn't hear any tone.

Thanks for all of the help,
Noah


Do you have an RF signal generator?

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 Post subject: Re: Airline 04BR-907A Problems
PostPosted: Nov Sat 25, 2017 1:54 am 
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Joined: Jul Mon 25, 2016 11:34 am
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Location: Wilton IA
Yeah, I think I can have access to one.

Thanks,
Noah


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 Post subject: Re: Airline 04BR-907A Problems
PostPosted: Nov Sat 25, 2017 3:33 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 1491
Location: Silver Spring MD, USA
Hi Noah -

It may not be needed, but I was just checking.

We need to confirm that the oscillator is not working. From your test it is most likely not, but we can check it with a couple of tests.

The easiest is to try a new converter tube, the 6SA7. Do you have another one you can use to test the set? If so, try it.

If that doesn't cure it, measure the voltage on Pin 3 of the 6SA7 (plate). It should be fairly high, about 250 volts. Then check the voltage on the grid of the same tube, pin 5. This should be negative, about -15 volts. If either of these voltages are not correct, we can investigate more.

By the way, the power transformer should be fine - we got output from the speaker so it should be good based on everything else you've described.

-Kevin

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 Post subject: Re: Airline 04BR-907A Problems
PostPosted: Nov Tue 28, 2017 2:34 pm 
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Joined: Jul Mon 25, 2016 11:34 am
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Location: Wilton IA
Sorry for the late response. I don't have another 6SA7, so I checked the plate and grid. On the plate I got 255 volts and on the grid I got -23 volts. When I was touching the grid though, I could now tune in stations. I assume this is because the lead of the multimeter is amplifying the signal.

What could be wrong though?

Thanks a lot for all of your help, it was nice to know I am getting somewhere!
Noah


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 Post subject: Re: Airline 04BR-907A Problems
PostPosted: Nov Tue 28, 2017 7:47 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 1491
Location: Silver Spring MD, USA
This is encouraging!

I'm at work writing this and working off the schematic Norm posted here:
http://www.nostalgiaair.org/pagesbymode ... 011000.pdf

I have a cleaner copy at home but I think the online version is still good to work with. What's really helpful at this point is that first "Clarified Schematics" page - the first one showing the BC band. So much easier to understand this than the full schematic!

A couple of things to check now.

1. Someone earlier in the thread mentioned the bandswitch contacts. There are two connections in the circuit via the bandswitch - labelled "U-V" and "P-T," both are on the second section of the switch. There *is* a layout of the connections on the schematic, you *could* trace those specific ones, but it's probably easier just to clean all of the contacts, and make sure they are making contact between the rotor and the contact tabs, and see if that cures it.

2. Check the BC oscillator coil, T-12, for continuity. The coil is on the front of the chassis, lower left, guessing from the drawing on the schematic.

3. Check the BC oscillator trimmer, C-16 to make sure it's not dirty or shorted.

Last thing to check would be the two mica caps, C-18 and C-19, and the 12.5K resistor R7. I would think the caps are ok, as they are usually very reliable, although folks are now reporting that they are going bad just as paper caps do.

-Kevin

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 Post subject: Re: Airline 04BR-907A Problems
PostPosted: Nov Wed 29, 2017 1:35 am 
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Joined: Jul Mon 25, 2016 11:34 am
Posts: 268
Location: Wilton IA
It is very hard for me to reach the switch (red circle) as you can see in this photo. What is the best way to clean it?

Thanks,
Noah


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 Post subject: Re: Airline 04BR-907A Problems
PostPosted: Nov Thu 30, 2017 12:24 am 
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Posts: 1491
Location: Silver Spring MD, USA
Yes, getting to it is always the problem!

You can use Q-tips...they may not reach far enough in to get to the contacts though. I have a dwindling bag of "double-tipped cleaning sticks" from Radio Shack. They're longer and heavier than Q-tips. Of course RS no longer exists.

The ones I have are similar to this: https://www.amazon.com/BBTO-Cotton-Wood ... tton+swabs

But regular Q-tips will work if you can reach the contacts. Don't spray the stuff in there - it will make a mess, may harm the switch wafers, attract dirt, and be impossible to clean up.

Spray the tip with contact cleaner and scrub the contact. There are a number of good cleaners out there - on my shelf right now I have DeOxit D5, MG Chemicals Nu-Trol, and some CRC QD Contact cleaner. You can get something like the latter at Home Depot or an auto parts store. All of them work equally well.

You will likely get fuzz from the Q-tips on the contacts - just blow it off after you're done.

This is a good thing to do for general service on any multi-band set.

-Kevin

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 Post subject: Re: Airline 04BR-907A Problems
PostPosted: Nov Thu 30, 2017 10:58 pm 
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Location: Sherwood, Oregon
Maybe I'm just seeing things, but it almost looks like a couple of flex resistors in that last photo (the kind Philco used in the mid 30's). It almost looks like one end popped off of the switch on the bottom. Just grasping at straws here.


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 Post subject: Re: Airline 04BR-907A Problems
PostPosted: Dec Fri 01, 2017 12:29 am 
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Joined: Jul Mon 25, 2016 11:34 am
Posts: 268
Location: Wilton IA
Thanks everyone for all of the help!
I found a 6SA7 tube and some contact cleaner. It is too late tonight the AM stations have turned their power down. Tomorrow I am going to do some more testing.

Also, what is a flex resistor? Should I replace it?

Thanks,
Noah


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 Post subject: Re: Airline 04BR-907A Problems
PostPosted: Dec Fri 01, 2017 1:16 am 
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Flex resistors - I can't find a picture right now - but Philco use them on their mid 1930's radios. I think they were wire wound and you could bend them. They were not very reliable. What I'm seeing might not be those. Maybe they are just insulating sleeves.


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 Post subject: Re: Airline 04BR-907A Problems
PostPosted: Dec Fri 01, 2017 1:56 pm 
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Joined: Jul Mon 25, 2016 11:34 am
Posts: 268
Location: Wilton IA
Okay, thanks for the info. I just checked, and those are just insulating sleeves.

Thanks for the suggestion,
Noah


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