Hi fellows,new to this forum,thank you.Having trouble with 91 model,126 code.Recaped the whole thing(filter caps and the funky bakelite thingie also.All the resistor in specs.)Reception has lots of loud inteference,buzzing!.Right now ckecking the oscillator/detector 36 tube circuit.Riders wirring specs indicate resistance specs of oscillator coil,which are hard to read.Plus the denotes of riders for coil #19,part 05985 says deferent.Anyone has correct specs and experience rewiring the coil? Thank you kindly for your help.Francis
Hi Francis and Welcome!
To check the osc coil measure the resistance from the cathode pin of the 36 tube to the connection on the osc coil that has the resistor and mica cap connected to it. With the set unplugged you should read a very low resistance between these two points if the winding is good like 10 ohms or less. Anything higher it's time to rewind.
Terry
When my pals were reading comic books
I was down in the basement in my dad's
workshop. Perusing his Sam's Photofoacts
Vol 1-50 admiring the old set and trying to
figure out what all those squiggly meant.
Circa 1966
Now I think I've got!
The oscitator coil 05985(3)has 3 set of windings.Inner tube/coil and outer tube/coil plus the one in trouble over the outer coil.The one in trouble you suggested for kathode circuit I trased and repaired/rewinded succesfully-was reading too high @100 ohms. 25 turns,38awg wire on stip of poly.scotch tape.Before did this surgery I noted this sceme on paper.Cleaned the base coil and lackered with polycoat spray.After rewinding it is reading 5.5 ohms.Riders wiring states 3.5 ohms.Is that ok?Btw: From Kathode of 36 tube to lug #1 via new coil,out on lug#2(clockwise counting) via 10k resistor bypas with 700 mmf-mica cap to ground.
Got to do more tracing on the other winding of same coil.Still bit puzling!?
Thank you so far!
All sounds good! The resistance of the new winding doesn't matter so much it's the inductance that's important. The other important thing is the direction of the winding, must be wound the same as original!
Once you get the set put back together you can check the osc by listening for it in another receiver. You can use a small transistor set placed next to the osc tube. Tune the Philco to 1000 kc then tune the transistor set to 1000kc + the IF frequency. I don't remember the IF frequency of the 91 I think it's 260kc which would equal 1260kc. When it's working as you tune the set around 1260 it will get quite or start to squeal.
Terry
When my pals were reading comic books
I was down in the basement in my dad's
workshop. Perusing his Sam's Photofoacts
Vol 1-50 admiring the old set and trying to
figure out what all those squiggly meant.
Circa 1966
Now I think I've got!
So far so good,but before I start tuning the philco w/the transistor set, btw,very tricky!And yes you're correct IM freeqency udjust at 260 Kc for Philco 91. Looking at the Riders wiring sceme,the prim/inner tube winding states 5 ohms-my reading is 16 ohms,lug#4 and lead wire from end of the winding to plate of 36 tube(B+).The outer tube windings lug#3 between trimmers 18 +23 and lug#5 to tuning cap4 reads 5 ohms.Maybe misprint at Riders wirring-should be reversed?? Prim/inner tube=15 ohms,Sec./outer tube 5 ohms ????Well,this set is pouring some tunes out now.Also rewinded the coil #12.Same task.25 turns,38awg wire,clockwise winding start at lug 3 to lug 1.Rest of the coils at this Philco 91 circuit test as they should by Riders wiring sceme.
If all the Philcos outthere needs same treatment,then God bless us all.
Anyway thank you bunch for holding my hand to go with this !!
I don't know. If it seems to look original and it tracks ok I would probably leave it a lone.
Terry
When my pals were reading comic books
I was down in the basement in my dad's
workshop. Perusing his Sam's Photofoacts
Vol 1-50 admiring the old set and trying to
figure out what all those squiggly meant.
Circa 1966
Now I think I've got!
Ohps....had to take a brake from that rascole. For some reason the darned thing comes and goes out of reception,when going all way out to high scale on dial.Come back when dial returned to lowest dial. Very weird!? Did some reading on forum and desided to downscale the cathode resistor on 36 tube from 10k to 7.5k Ohms.Touched up a bit the near by trimmer and urika! Thanks a bunch to all of you fellows for your knowladge and supportive help. Btw: this Philco 91 has quite a decent fidelity= worth to doodle around!So,it didn't hurt to trick up the IT primary. Next Philco on my bench,please-I'm hooked!
Very happy to help you out!! Glad you got working. It is a good preforming and sounding. set. Years ago I had the chairside version of the 91 with dual speakers in a large separate cabinet.
Terry
When my pals were reading comic books
I was down in the basement in my dad's
workshop. Perusing his Sam's Photofoacts
Vol 1-50 admiring the old set and trying to
figure out what all those squiggly meant.
Circa 1966
Now I think I've got!
Sables2, yes, I think all the Philcos of that age with the fine wire wound over the other coils with some type of clear tape to separate, have that problem. Don't know what was in that tape but it just eventually ate up the wire. Had two that had to be rewound. Mine was a Philco 19. Always wanted a nice cathedral. Don't think I will try another early Philco although I am a Philco fan.
Jerry
I just spent two and a half days trying to get an oscillator running in a 71-123 with the 36 tube. It seems that most Philcos of this age use the same 36 tube oscillator. So after doing the continuity check on the coil windings it too needed rewinding both the primary and the secondary. After completing said tasks the osc ran at about 4.5 mhz. I measured it with voltmeter that has a counter in it. I also could see lots of harmonics and ringing while tuning across the band with a scope clipped over the plate wire of the 36 tube not a direct connection just hanging on the insulation. It was really unstable. I spent two days trying to find what was bad. first I thought I had wound the coil wrong. So I checked it against the coil of an 89 radio coil that works and after much checking and more checking all the caps and resistors I came up with the thought that the inner coil must be bad even though it checked good. Then just before I was about to rewind the inner coil a thought came to me. What about the coupling between the inner and outer coils. I took my signal generator at 1.2 mhz and hook it up the primary winding and measured the output of the inner coil while moving it in and out of the outer. There was a huge difference. The peak was not at the normal location it was about 3/4 of and inch out from the bottom of the outer coil. Now this did not mean that this was the fix but after I reinstalled the coil assembly with the inner loose and a short jumper wire where the two lugs are normally soldered together so I could move the inner coil in and out while watching the scope. And there is was!!!!!!! after days the oscillator was clean and stable through the tuning range with the inner coil hanging out about 5/8 inch of the bottom of the inner. See attached image. You can see the tip of the lug from the outer coil hiding behind the dogbone resistor and the lug from the inner coil just to the right of the dogbone wire.
Hope this helps someone.
!!!!!!!!!!!!!!!!!!!RESISTANCE IS FUTILE!!!!!!!!!!!!!!!!!!!!!!
/\/\/\/\/\/\/\/\/\
The 36 tube was a bum design, even the Philco documentation suggests replacing the tube even if it tests good. I have had this experience with my model 14 LZX, it took an NOS 36 to get it to receive!
Later versions of the model 89/19 have a 77 tube for the oscillator, a much better design.
FYI Ron has a thread in this site that details how to replace your 36 tube oscillator with a 6A7.
