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 Post subject: Columaire 101
PostPosted: Apr Sun 05, 2020 5:10 pm 
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Joined: Apr Sun 05, 2020 4:59 pm
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Hello,

i am repairing a Columaire 101, attached is the schematic. i replaced the capacitors and checked all the resistors and wiring. The unit had no audio. i checked the interstage audio transformer and realized it was open. i replaced it with a Hammond 124 and now i have audio BUT, the audio volume is very low independent of the volume pot. Also very few stations come in. i replaced the volume pot and it did not have any impact.

Now the Hammond 124 turns ratio is lower that the original interstage transformer but i would not think that it would have such an impact.

i checked the speaker and the cone coil and field coil resistance matches the schematic.

i did check the field coil voltage and it is -50V. not sure if this is correct.

Any other ideas. Thanks and much appreciated.


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 Post subject: Re: Columaire 101
PostPosted: Apr Sun 05, 2020 6:33 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 13664
Location: San Jose, CA USA
Some things worth trying:

1. If you touch or put an antenna on the grid of the 1st detector tube, does reception get stronger? Try this on the RF stage grid as well. If so, there is probably a blown primary on the antenna transformer or a problem with one of the tuned circuits up to the mixer stage.

2. Did you try aligning anything yet? Often that has a huge effect on a radio this old. If you don't have a signal generator, simply tune in a weak station and try to peak all the IF transformers. If you have a signal generator, better to peak them at the known correct frequency of 175 kHz.

3. If you suspect the speaker may be a problem, try subbing in a permanent magnet speaker, leaving the field coil of the original speaker attached.

4. The automatic volume control circuit in this radio could cause poor sensitivity if it's not working right. Try pulling out the AVC tube, and connecting a variable power supply to where the plate of the tube was connected. Adjust it through a range of voltages from -20 to +20 VDC and see if the volume comes up to a nice level at some particular point.

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 Post subject: Re: Columaire 101
PostPosted: Apr Sun 05, 2020 11:24 pm 
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Thanks Tom, great suggestions. Will give it a try.


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 Post subject: Re: Columaire 101
PostPosted: Apr Wed 08, 2020 9:24 pm 
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Tom, thanks for the tips. it turns out the alignment has made a big difference but i am still not getting the selectivity/gain that i should be getting.

i only tuned to a weak station and then peaked the IF transformers. i have a signal generator but i am not sure how to use it to tune the radio. can you describe how to do that?

i will also be checking out the AVC circuit as i suspect something is wrong with that also as the volume pot still does very little (raise or lower the volume)

Thanks!!


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 Post subject: Re: Columaire 101
PostPosted: Apr Wed 08, 2020 10:01 pm 
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Location: Vancouver Island, Canada
A good way to learn about alignment is to use the search feature top of this and every page, and then read as many posts as you can.
You can even enter your radio make and model and see if someone has posted specific alignment info.
Also, search for info about your sig gen.

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Last edited by westcoastjohn on Apr Thu 09, 2020 3:24 am, edited 2 times in total.

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 Post subject: Re: Columaire 101
PostPosted: Apr Wed 08, 2020 10:46 pm 
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Location: San Jose, CA USA
On your schematic, you see some handwritten notes in the lower right showing the locations of the IF trimmers. If you've already tuned in a weak station and peaked all of them for maximum signal strength, then the next thing I'd try is to adjust the trimmers on the variable capacitor gangs. I don't know where the trimmers are located on your tuning capacitor, but hopefully you can find four trimmers, one associated with each gang. The little diagram on the schematic indicates which gang is which.

For this adjustment, you should tune in a weak station near the top of the dial (adjusting lower on the dial will not give as good performance across the full dial).

For a first attempt on this radio, I would avoid adjusting the oscillator trimmer. When you've tuned in a weak station near the top of the dial, adjust the link, RF, and 1st detector trimmers for maximum signal strength. How's it working now?

If it's good enough, you're done. If you think it still ought to be better (for a radio of this age and design, which will not be as good as a later models), some things to try:

1. Instead of simply peaking the IFs on a weak station, peak them on the proper frequency of 175 kHz. For this you need signal generator that is reasonably well calibrated. Is your RF generator digital, or do you have a frequency counter? If not, I would skip this as you may end up worse than your starting point. If you do have a well calibrated generator, then feed in the signal through a capacitor (any size) to the grid of the 1st detector tube. Use modulated RF at 175 kHz. Set amplitude just high enough that you can hear the tone. Adjust all IF trimmers for maximum signal strength.

2. Do you get a clear peak on each IF trimmer? If there is no peak, or if it seems best all the way loose or all the way tight, that may be a problem. Let us know if this happens on any trimmer.

3. After realigning the IF trimmers, it will be helpful to repeat the link, RF, and 1st detector trimmer adjustments on the tuning cap gangs as above using a weak station near the top of the dial.

If it's still no good, let me know and we can go one step further and adjust the oscillator trimmer (wait for instructions on how to do that).

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 Post subject: Re: Columaire 101
PostPosted: Apr Thu 09, 2020 2:59 am 
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Thanks Tom, appreciate the feedback. will let you know who it goes!


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 Post subject: Re: Columaire 101
PostPosted: May Sat 09, 2020 9:42 pm 
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Tom, thanks for your help. Got everything tuned up nicely and everything has been put together. take care.


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 Post subject: Re: Columaire 101
PostPosted: May Sat 09, 2020 11:06 pm 
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Joined: Jan Thu 01, 1970 1:00 am
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Location: San Jose, CA USA
Thanks for the update, and nice to hear you got it working well. :)

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 Post subject: Re: Columaire 101
PostPosted: May Sun 10, 2020 6:19 pm 
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Location: Cottage Grove, Minnesota
The radio chassis in your Columaire 101 is similar to the RCA Radiola 80, except for the AVC circuit and tube. There is a ton of information regarding the Radiola 80 chassis available on the internet, just search for it. As you have found out the interstage transformer is usually open and the Hammond 124 is a good replacement. I recommend that you replace all of the dog-bone resistors, they tend to drift considerably. I used 2 Watt resistors for all of the ones in my Graybar 700.

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