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  #1  
Old 06-25-2014, 11:15 AM
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DavGoodlin DavGoodlin is offline
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Philco FM detector trans help needed

I have this 1962 Philco Stereophonic console HiFi that would play for about 10 minutes on FM until the static associated with silver mica disease begins.

After isolating stage by grounding grids of the two preceding stages, then confirming with some chopstick acupuncture at the suspect transformer's base, I carefully removed and disassembled it. The Sams schematic shows the three capacitors (without the values) within the transformer's base.
I have a document which shows typical values of these caps for Zenith radios and chose new cap values as listed on a similar configuration, which was obviously a discriminator transformer. (2@68pf and 1 @24 pf)

I drilled out the brass rivet, surgically removed the silver plated mica sheets and tabs from the base of my transformer and soldered it back onto the PC board. Then I added the new caps right onto the PC board. Now the AM and FM do not work at all. Turning the slugs MINIMALLY to re-tune the transformer to resonate at 10.7 Mc would be necessary but does nothing to change the issue. The continuity tests as it did before this operation.

Question: is there a resource where I can find the value of these caps specific to this transformer. I do not have a J W Miller catalog, which typically had a listing of catalog numbers for the OEM crossed to the replacement unit AND the characteristics of that replacement. Philco # is 32-4714-3, Miller; 1464-PC, Stancor RTC9050, Workman T658
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Last edited by DavGoodlin; 06-25-2014 at 11:11 PM. Reason: new part numbers
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Old 06-26-2014, 10:07 AM
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Electronic M Electronic M is offline
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If the originals were good enough for the set to work, you have an accurate cap meter, and did not destroy the originals while removing them, then why not try measuring the original values...
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Old 06-26-2014, 03:36 PM
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DavGoodlin DavGoodlin is offline
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Unfortunately, removing these offending caps did destroy them.
But....that may still be an option in this case, to measure the ones in a similar Philco tuner I have, which uses the same tubes.

The last few similar repairs worked out well, since I knew the correct pf values before starting.
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Old 06-26-2014, 08:01 PM
Don Lindsly Don Lindsly is offline
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I can look up the Automatic Coil application notes. I need to know:
1. Is the AM IF also included in the coil?
2. Is the circuit a discriminator or ratio detector?
3. Is the coil mounted on a PC board?
4. Confirming OEM Automatic Coil Mfr# 119 preceding the date code.
Don
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Old 06-26-2014, 11:56 PM
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DavGoodlin DavGoodlin is offline
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Quote:
Originally Posted by Don Lindsly View Post
I can look up the Automatic Coil application notes. I need to know:
1. Is the AM IF also included in the coil?
2. Is the circuit a discriminator or ratio detector?
3. Is the coil mounted on a PC board?
4. Confirming OEM Automatic Coil Mfr# 119 preceding the date code.
Don
Thanks Don,
The Am is not included (but somehow affected) and the function of the 6BJ7 is listed as a discriminator
and transformer is mounted on a PC board.
Yes, the 119 preceeds datecode as 119-61-36

My last resort will be to pull the same transformer out of my yet untested Philco RT-400 tuner, disconnect coil and measure the bases built-in capacitance.
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Old 06-27-2014, 01:24 AM
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jr_tech jr_tech is offline
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Quote:
Originally Posted by DavGoodlin View Post
The Am is not included (but somehow affected)
Just a WAG, but I suspect that there is something more going on here then capacitor values being a little off. Perhaps a run was broken or an old cold solder joint was disturbed.

jr
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Old 06-29-2014, 05:06 PM
Don Lindsly Don Lindsly is offline
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The Automatic Application Notes show 33uuf between terminals 1 and 2, 33uuf plus 16uuf between 3 and 4 and 33uuf between terminals 3 and 6. The 16uuf may vary depending on external capacities.

jr_tech makes a point. Check for built in trouble.

Last edited by Don Lindsly; 06-29-2014 at 05:11 PM.
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Old 06-29-2014, 11:46 PM
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DavGoodlin DavGoodlin is offline
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Yes, this set needs to be approached as if it has a new problem.
I had recapped it and was working super except for the intermittent static on FM, before I desoldered the xfmr.
Don- It looks as if I need to order some caps, but I have 5 terminals, maybe 6 means 5 here-THANKS!
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Old 06-30-2014, 03:59 PM
Don Lindsly Don Lindsly is offline
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Dave:

There is no terminal 5 on that transformer. The fifth lug is designated terminal 6. Look for very small numbers molded into the bottom of plastic base next to the lug.
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Old 12-18-2016, 04:37 PM
Southerner Southerner is offline
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Quote:
Originally Posted by Don Lindsly View Post
I can look up the Automatic Coil application notes. I need to know:
1. Is the AM IF also included in the coil?
2. Is the circuit a discriminator or ratio detector?
3. Is the coil mounted on a PC board?
4. Confirming OEM Automatic Coil Mfr# 119 preceding the date code.
Don
Don, do you have a link to the Automatic Coil Application notes? I have an 455kc IF transformer in a radio from the early 60's and need to find a replacement and have not had much luck as I gather Automatic Coil is long since out of business so I would love to get a copy of those application notes.

Thank you.
Jim
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  #11  
Old 10-31-2017, 09:53 AM
Southerner Southerner is offline
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Quote:
Originally Posted by Don Lindsly View Post
Dave:

There is no terminal 5 on that transformer. The fifth lug is designated terminal 6. Look for very small numbers molded into the bottom of plastic base next to the lug.
Is terminal 6 a center tap? Or is terminal 6 something other than center tap? Did Automatic Coil give the specs for their coils?
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  #12  
Old 11-02-2017, 01:30 AM
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Kevin Kuehn Kevin Kuehn is offline
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Sorry to say I believe Don passed away in late 2015 or possible early 2016.
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  #13  
Old 11-02-2017, 01:45 AM
Southerner Southerner is offline
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Quote:
Originally Posted by Kevin Kuehn View Post
Sorry to say I believe Don passed away in late 2015 or possible early 2016.
I am sorry to hear that. He seemed to be a great source of information.
Thank you for letting me know.
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