Philco model 18 (code 121) - HELP! - Printable Version
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+--- Thread: Philco model 18 (code 121) - HELP! (/showthread.php?tid=5934)
RE: Philco model 18 (code 121) - HELP! - jerryhawthorne - 04-23-2013
Brenda, the only difference I can see between the two schematics in the area in question is that the code 124 set has a shunt resistor across the shadow meter (2.9K). The code 121 lacks this resistor. It is my understanding that the shunt was used so that if the shadow meter coil opened, plate voltage would still be supplied to the RF amp and the radio would be usable. In the code 121 if the coil opens your SOL. Your diagnosis certainly looks good.
Jerry
Edit: A little closer look and I would eliminate the shadow meter as a possibility. If open, there would be no plate voltage on the 6A7 as well. Looks like the coil is the culprit. The 124 schematic differs in the distribution of the plate voltage relative to the meter, supplying the RF tube only with B+ for the plate after the meter. The 121 schematic shows both the RF and Osc/Det plates being fed after the meter.
RE: Philco model 18 (code 121) - HELP! - BrendaAnnD - 04-23-2013
The simple test of this would be to bypass the shadow meter (tie the two leads together) and see if your voltages (and your signals) come up.
These shadow meters aren't very complicated, and it wouldn't be difficult to wind a new coil. For that matter, the coil could be open very near to the connections and easily repaired.
RE: Philco model 18 (code 121) - HELP! - jerryhawthorne - 04-23-2013
Hopefully a picture of the proper schematic. This is the code 121
Jerry
[Image: http://i303.photobucket.com/albums/nn129/JerryHawthorne/18code1211.jpg]
Upon preview, all the conversion didn't help the quality much but it does give an idea of overall flow.
RE: Philco model 18 (code 121) - HELP! - Pithicus999 - 04-23-2013
Thanks both of you, I'll check the coil when I get home and try the 'bypass' trick.
Brenda, l can send you a PDF if you like, or Jerry can I sent him one already. Just let me know, if his picture isn't enough info.
Thanks Jerry for posting!
One more thing. If something is wrong with the coil, can i remove it, (probably need to clean it off, looked like some dust etc. can I use alcohol and cue tips? Or no?) anyway, do I want to attempt re-winding the thing myself…I’m pretty good a copying what is already there, but I’ll take a look, hopefully a loose or crappy wire is all.
Thanks for the diagnosis Brenda!
RE: Philco model 18 (code 121) - HELP! - jerryhawthorne - 04-23-2013
The bypass trick was for the shadow meter, not the coil in question, it is the primary of item 10. To check, I would hook one lead of your meter to the plate of the 78 RF tube and use the other probe to touch each of the 6 (I believe) connections to the bottom of the coil in question, one at a time. One should be at 0 ohms (the line from the plate and another should be a couple of ohms for the primary of the coil. If you don't get two connections with the low resistance, the coil is open. Let us know, there are opportunities for rewinding available. Philcos are notorious for coil problems.
Jerry
RE: Philco model 18 (code 121) - HELP! - Pithicus999 - 04-23-2013
Jerry- everything measured way off the charts above Ohms that I could read, except the Plate to coil which was zero of course. There is a wire on top of coil that I could not get to with my lead, so I followed the wire down to the Wave Band Switch and tried to measure ohms there. That was also way above 200k ohms (my highest setting).
So...that just leaves the shadow meter then, right? On the schematic the shadow meter looks like the symbol for a 'switch'. Can that thing be "ON" or "OFF"?
RE: Philco model 18 (code 121) - HELP! - BrendaAnnD - 04-23-2013
If you are getting high ohms across the plate coil, the coil is open. These coils are typically pretty easy to remove for further inspection, or even rewinding.
If it is only the primary (plate) coil that is open on this coil, it's extremely easy to rewind, as it's only a relatively few turns over the secondary, and is not super critical as it is not a tuned circuit. Of course, the closer to the original, the better the performance will be.
There are also folks who do professional rewinds, like Neil Sutcliffe.
RE: Philco model 18 (code 121) - HELP! - jerryhawthorne - 04-23-2013
Pith, forget about the shadow meter, it is probably OK. As Brenda indicated the coil you were measuring is open on the primary. I have Ron, the admin of the Phorum rewind mine, my eyesight is not good enough or as indicated get some wire and wind your own. Someone here can recommend size and number of turns. You will need remove the coil and make careful notes on the wire locations. Lots of wires to hook up wrong.
Jerry
RE: Philco model 18 (code 121) - HELP! - Pithicus999 - 04-24-2013
Darn.
I feel comfortable doing it, however I would feel more comfortable if I could see a video (YouTube or something) and watch someone else doing this? Can someone please post one if you have it?
Do I want to completely remove all wiring and then re-wire the thing?
I’m having trouble wrapping my head around what is wrong with the coil. I’m guessing one of the turns in the wire (because they are so thin) separated or something? So that instead of 1 continuous wire, you would now have essentially 2? Is that what we are talking about when you say the coil is ‘OPEN’?
Also, are these the steps
?-Unsolder all 6 soldered leads
-unbolt coil and remove from chassis
-count/document/take pictures of etc. Coil and wiring as well as number of winds (I know this is extremely important)
-remove wire
-maybe clean if dirty?
-re-wire
-re-place
-re-solder
Missing anything?
RE: Philco model 18 (code 121) - HELP! - Pithicus999 - 04-24-2013
Also, any idea on the gauge of wire needed? I'm guessing really high, like way above 24?
RE: Philco model 18 (code 121) - HELP! - jerryhawthorne - 04-24-2013
Pith, here is a example of one I sent off for rewind. The primary (top wind) was open. I believe your coil will have a lot less winds on it making it easier. This is not the same coil as yours but an example of what your going to see. You will be unwinding the top section of yours if after inspection and you can't repair it (broken wire going to lug). Count the number of turns and note the direction of winding (both important). When you remove the assembly confirm that it is open and also measure the other 4 connections (the secondary). Should be low resistance between all four of it's connections. Secondaries seldom seem to go bad. Your proceedure outlined above looks fine to me and yes the wire that winds around the coil form that is the primary (the one on top) is broken so there is no low resistance measurement between the plate of the RF tube through the fine wire on the coil to another connection on coil. Wire size and number of turns may be answered by someone else.
Jerry
[Image: http://i303.photobucket.com/albums/nn129/JerryHawthorne/P1010002-7.jpg]
RE: Philco model 18 (code 121) - HELP! - Pithicus999 - 04-24-2013
Thanks Jerry!
I'll need to know the size of wire and any idea where to get it?
Thanks!
RE: Philco model 18 (code 121) - HELP! - Pithicus999 - 04-24-2013
Can I use this wire from Radio Shack..
http://www.radioshack.com/product/index.jsp?productId=2036277
RE: Philco model 18 (code 121) - HELP! - jerryhawthorne - 04-24-2013
Have not done it so will leave that to more knowledgeable people (everyone).
Jerry
RE: Philco model 18 (code 121) - HELP! - Pithicus999 - 04-25-2013
Ok, I removed the coil and checked to see if any wires were broken, but I didn't find any evidence of any broken or missing wires, I figured I was looking for 2 wires. Here is what I found.
There are 2 wire wraps (as you said) but from top to bottom, yours are wrapped around the coil like a 'shirt' and 'pants' wrap along your body. Your pants are below the shirt along your length.
THIS one however is wrapped from top to bottom around the coil like 'Underwear' and 'pants' where the bottom wire is wrapped an partially "buried" beneath the top wire, just as your underwear is beneath your pants. Only, it looks much closer like it would be if you put your 'Underwear' OVER your 'pants' because the wire underneath goes the full length of the coil, and the wire on top only runs 1/5 of the length of the coil....make sense?
Maybe you knew that was the case already? I just wanted to make sure we all know what this thing looks like. Ok, now that we're all done laughing, about putting on your underwear over your pants, back to this coil issue.
From this point, I noticed 6 wires (but I know there are only 2 actually) wrapping around and connecting to all 6 posts or tabs. The 2 ends of each wire (making 4 ends of the 6 total) wrap around the coil and hook to 4 of the 6 tabs. Good so far.
Somewhere in the middle of each wire, before the end of each wire is finished wrapping around the coil, a loop from each wire is made when the end of the wire submerges INTO the coil (through a hole) and then wraps around the 5th (or 6th) tab, and then comes back to emerge from that same hole in the coil for the final wind around the rest of the coil and then back up to connect to the end of the 5th (or 6th) tabs, completing all 6 connections.
So we have 2 wires: 4 wire ends and 2 wire 'Loops' for a total of 6 contact points. None of the lines seemed broken, and all 6 connections were soldered to each of the 6 tabs.
So....I looked at the schematic and thought that I maybe I made a mistake the other day in my OHM readings. I then tried to bypass the coil by connecting the alligator clip from the plate on the R.F. #78 tube to the tab on the #12 cap. I also tried to bypass the shadow meter by connecting the alligator clip at the plate on the I.F. #78 tube directly to the #12 cap.
Those are the by-passes I used to see if either the coil or the shadow meter were bad. I would tell the results, but I forgot!
I think I was up to 2 am last night?? Not sure.
I'll check again later tonight and post results from both bypasses. I do know this, one showed 270 volts on BOTH #78 plates, and the other bypass showed no change...
....more to come.