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 Post subject: New guy with S/C 337X
PostPosted: Oct Mon 23, 2017 3:02 pm 
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Joined: Oct Mon 23, 2017 2:48 pm
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Good morning. Just registered today, I am 57 years old and have been involved with old radios since i started picking them out of the trash when I was in grade school. Bill Bushnell at New Trier West in the mid 1970's was my electronics instructor and we remained in contact working on assorted projects and having meals together until 2006 when he was called home at the age of 80.
I am working on a Stromberg Carlson 337X and changed all caps and out of tolerance resistors. The radio works well but the tuning eye does not close very far on strong stations. New 1 meg resistor in the 6U5 socket. New brite RCA 6U5. What would be the suspects? Tim Oneil.


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 Post subject: Re: Unknown capacitor(?) in Stromberg-Carlson radio
PostPosted: Oct Mon 23, 2017 3:25 pm 
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Location: San Jose, CA USA
If the eye pattern is closing, but not vet far, I'd try an alignment touch up as the next step. As a first step, tune in a weak station and adjust the IF transformer trimmers for max signal strength. Do you get a clear peak within the adjustment range on each one (not all the way tight or all the way loose)? Does the eye tube close further after this adjustment?

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 Post subject: Re: Unknown capacitor(?) in Stromberg-Carlson radio
PostPosted: Oct Mon 23, 2017 3:38 pm 
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Did a touch up and did not change the function. Closes a small amount on a strong station and not at all on a weak station. Reception is OK but not exceptional. Changing the caps and resistors made the radio work better but the eye works the same as before the re-cap. What drives this function? The 6H6 on this set is the avc and should make up for the weaker stations, correct? Also the screen voltages on the oscillator and IF tubes are running about 20 volts high. Tim.


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 Post subject: Re: Unknown capacitor(?) in Stromberg-Carlson radio
PostPosted: Oct Mon 23, 2017 4:01 pm 
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The eye tube responds to the AVC voltage. Since your reception is weak in general, it is behaving as it should. Check continuity of front end coils (particularly the primary winding of the antenna transformer, which is sometimes blown) and try touch up of front end alignment if you are familiar with that.

If you touch antenna to top of 6K8 instead of antenna terminal, is reception better?

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 Post subject: Re: New guy with S/C 337X
PostPosted: Oct Wed 25, 2017 3:22 am 
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Thank you for the reply. Been at work the last two days and will get back to this project tomorrow night and let you know the results. Is the Ryders the only schematic available. Thank you, Tim.


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 Post subject: Re: New guy with S/C 337X
PostPosted: Oct Sat 28, 2017 12:16 am 
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Putting the antenna on top of the 6K8 does not change anything. The reception is an 8 out of a 10 scale. Not as much bass as I would expect but good volume. What should I do to test the eye tube in the circuit? The eye opens and closes perfectly on my 534A tester.


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 Post subject: Re: New guy with S/C 337X
PostPosted: Oct Sat 28, 2017 12:50 am 
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Signal is probably still a little weak. I presume you have a reasonable antenna on this -- at least 10 feet of wire?

You've touched up the alignment of the IF transformers, so what remains is the front end alignment. Refer to the following figure from Rider:

Attachment:
Stromberg-Carlson 337 alignment picture.jpg
Stromberg-Carlson 337 alignment picture.jpg [ 57.41 KiB | Viewed 348 times ]


1. Make sure the dial pointer has proper mechanical position. It should not overshoot on either end of the dial. Sometimes there is a little mark on the dial to indicate where the pointer is supposed to be at end of travel. If it is off, physically move it on the string until it lands perfectly on the mark at end of travel.

2. Tune in a station near the top end of the broadcast band. Adjust the "Oscillator Transformer A Range HF Aligner" trimmer to move the station to the exact correct position on the dial.

3. Watching your eye tube, adjust the "Antenna Transformer A Range HF Aligner" trimmer for maximum signal strength -- indicated by the eye tube closing up the most.

For #3, do you get a clear peak within the adjustment range of the trimmer -- not all the way tight or all the way loose?

You might also try repeaking the IF transformers and using the eye tube to gauge the signal strength.

How's your signal strength now?

Regarding bass, do you have the speaker in the cabinet? If a speaker is lying out on the table, bass will be extremely poor. The sound from the front of the speaker cancels the sound from the back of the speaker and vice versa. You need a baffle board between the two to have any bass. Cancellation occurs mainly with bass, since bass waves go around corners well, while higher frequency sound waves don't.

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 Post subject: Re: New guy with S/C 337X
PostPosted: Nov Sun 05, 2017 4:56 pm 
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Thank you for your reply. I just got back from a full week of work and just pulled this up this morning. I will try this procedure this afternoon. Tim.


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 Post subject: Re: New guy with S/C 337X
PostPosted: Nov Sun 05, 2017 6:03 pm 
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Hi Tom. I tried your suggestions and no change, maybe a little worse. I do have 10 feet of antenna. The filter caps are original but test perfectly, I am going to change but that should not affect this problem, correct? I feel that I am missing a simple item. Tim.


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 Post subject: Re: New guy with S/C 337X
PostPosted: Nov Sun 05, 2017 7:17 pm 
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Location: Sunnyvale CA
vtube5 wrote:
Hi Tom. I tried your suggestions and no change, maybe a little worse. I do have 10 feet of antenna. The filter caps are original but test perfectly, I am going to change but that should not affect this problem, correct? I feel that I am missing a simple item. Tim.


"Test perfectly"? I am not sure what this means in this context, do you mean that they showed the right capacity, and/or no leakage at the rated voltage?

Brett


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 Post subject: Re: New guy with S/C 337X
PostPosted: Nov Sun 05, 2017 9:30 pm 
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Location: San Jose, CA USA
In my step #3 above, did you get a clear peak? If not, there is still a problem that needs to be corrected in the front end.

If your voltages are where they should be, poor sensitivity probably is not caused by issues with the filter caps. However, you will want to keep an eye on those to make sure they do not run warm or hot. If they do, they need to be replaced pronto. Sometimes original filter caps are still OK to use, but one must exercise caution.

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 Post subject: Re: New guy with S/C 337X
PostPosted: Nov Tue 07, 2017 3:28 am 
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Yes, there was a clear peak in step #3. The filter caps tested with no leakage and within spec. I will replace anyway, just have not done yet. The B+ voltage is good and the radio sounds decent. The grid voltage on the 6U5 peaks on a strong station at -2 volts, not enough to close the eye very far. I do not clearly understand the the AVC circuit and how the output to the 6U5 grid works. Thank you for helping this untrained but willing to learn radio man.


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 Post subject: Re: New guy with S/C 337X
PostPosted: Dec Wed 06, 2017 3:50 pm 
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I installed new filter caps and the radio works the same. Picks up stations decently but not perfectly. Spent time on alignment per instructions and the tuning eye improved slightly. The adjustment on step #3, the A range HF aligner, to get a peak on the eye tube the adjusting screw is turned out all of the way. The radio crackles with static at the very high and very low end of the tuning scale. I feel that I am missing something simple. Tim.


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