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-   -   Philco FM detector trans help needed (http://www.videokarma.org/showthread.php?t=261983)

DavGoodlin 06-25-2014 10:15 AM

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:sigh:) 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

Electronic M 06-26-2014 09:07 AM

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...

DavGoodlin 06-26-2014 02:36 PM

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.

Don Lindsly 06-26-2014 07:01 PM

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

DavGoodlin 06-26-2014 10:56 PM

Quote:

Originally Posted by Don Lindsly (Post 3108272)
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.

jr_tech 06-27-2014 12:24 AM

Quote:

Originally Posted by DavGoodlin (Post 3108304)
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. :scratch2:

jr

Don Lindsly 06-29-2014 04:06 PM

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.

DavGoodlin 06-29-2014 10:46 PM

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!

Don Lindsly 06-30-2014 02:59 PM

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.

Southerner 12-18-2016 03:37 PM

Quote:

Originally Posted by Don Lindsly (Post 3108272)
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

Southerner 10-31-2017 08:53 AM

Quote:

Originally Posted by Don Lindsly (Post 3108657)
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?

Kevin Kuehn 11-02-2017 12:30 AM

Sorry to say I believe Don passed away in late 2015 or possible early 2016. :sigh:

Southerner 11-02-2017 12:45 AM

Quote:

Originally Posted by Kevin Kuehn (Post 3191492)
Sorry to say I believe Don passed away in late 2015 or possible early 2016. :sigh:

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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