#1
|
||||
|
||||
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
__________________
"When resistors increase in value, they're worthless" -Dave G Last edited by DavGoodlin; 06-25-2014 at 10:11 PM. Reason: new part numbers |
#2
|
||||
|
||||
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...
__________________
Tom C. Zenith: The quality stays in EVEN after the name falls off! What I want. --> http://www.videokarma.org/showpost.p...62&postcount=4 |
#3
|
||||
|
||||
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.
__________________
"When resistors increase in value, they're worthless" -Dave G |
#4
|
|||
|
|||
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 |
#5
|
||||
|
||||
Quote:
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.
__________________
"When resistors increase in value, they're worthless" -Dave G |
Audiokarma |
#6
|
||||
|
||||
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 |
#7
|
|||
|
|||
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 04:11 PM. |
#8
|
||||
|
||||
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!
__________________
"When resistors increase in value, they're worthless" -Dave G |
#9
|
|||
|
|||
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. |
#10
|
|||
|
|||
Quote:
Thank you. Jim |
Audiokarma |
#11
|
|||
|
|||
Is terminal 6 a center tap? Or is terminal 6 something other than center tap? Did Automatic Coil give the specs for their coils?
|
#12
|
||||
|
||||
Sorry to say I believe Don passed away in late 2015 or possible early 2016.
|
#13
|
|||
|
|||
Quote:
Thank you for letting me know. |
|
|