Philco 70 tuning backward? - Printable Version
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Philco 70 tuning backward? - btoher - 10-07-2016
Hi, I am just getting back to restoring a Philco radio after a long break from them. But i like philcos and always wanted a 70 or a 90. Not feeling too lucky at the moment, but will eventually . It is an earlier serial number 70.Not in the best of shape but I am determined to get it back to normal as possible.The problem is I am stuck and could use some help . Maybe someone has run into this symptom before. 1420 khz station comes in at 1120 on the dial 1190 kHz comes in at 1410. Backwards! I flipped the oscillator feedback coil wires .no change.The silver micas should be .00011 on the oscillator but were .ooo42 . I had a .00025. So I installed it .No real change.I have done the normal cap and resistor changes - no change.I have checked coils no opens. Not sure if they are rewound but does hot look it.Any ideas much appreaciated ! Nothing below 900 on dial .With signal gen only low tone below 900.Is there some thing obvious I should look at? Thanks for any help!
Bill
RE: Philco 70 tuning backward? - morzh - 10-08-2016
Oscillator backwards (even if worked) has nothing to do with it, as no matter how it oscillates and for what reason, the tuning cap meshing will decrease the frequency and unmeshing will increase it.
You are likely badly out of alignment.
Plus might be seeing images.
Put the oscillator back as it originally was, make sure it does oscillate, and align the radio.
RE: Philco 70 tuning backward? - btoher - 10-08-2016
(10-07-2016, 09:34 PM)btoher Wrote: Hi, I am just getting back to restoring a Philco radio after a long break from them. But i like philcos and always wanted a 70 or a 90. Not feeling too lucky at the moment, but will eventually . It is an earlier serial number 70.Not in the best of shape but I am determined to get it back to normal as possible.The problem is I am stuck and could use some help . Maybe someone has run into this symptom before. 1420 khz station comes in at 1120 on the dial 1190 kHz comes in at 1410. Backwards! I flipped the oscillator feedback coil wires .no change.The silver micas should be .00011 on the oscillator but were .ooo42 . I had a .00025. So I installed it .No real change.I have done the normal cap and resistor changes - no change.I have checked coils no opens. Not sure if they are rewound but does hot look it.Any ideas much appreciated ! Nothing below 900 on dial .With signal gen only low tone below 900.Is there some thing obvious I should look at? Thanks for any help!
Bill
Good Morning ,I wanted to add some more detail and ask another related question. The IF coil appears to have had some repair .The primary is 18 ohms and the secondary is 7.8 ohms .The 1st detector coil is primary 17 ohms secondary 4.4 ohms . Not that this is the problem ,but I do not know. I have read and looked for what the coils should read on this model and can not find any approximate values listed .Right now I have the set on a long wire antenna , but am moving it back to the bench and look at it with signal gen and scope . I have a lot of back ground information that I can add . For instance the tuning gang was rebuilt ,cleaned new insulators etc. What is weird is the rotor just sits in the rear of the gang with a wire strap to hold it in place. No bushing or anything . I have had to grease that because dry the hold down wire was wearing at the shaft . I went through all the spacing of plate checks I could . Nothing touching . Even with the lack of a good bushing in the back of the gang . The first noticeable thing in the alignment was how strong the 266 khz I.F was . But it was adjustable . Second thing was how weak the lower signal was on alignment , there is no AVC on this model . Last the #4 tuning trimmer and # 7 low frequency adjustment seem to have no effect . So as you can see I am clutching at straws and need to get methodical . Right now I am sort of brain dead as to what to do . Not even 100% sure that the tuning is linear backwards as I think a strong local station comes in way off the mark in a place that makes no sense.I have order the correct .00011 micas for the oscillator .But because all my fiddling around there has not seemed to result in any change I have low confidence that will do the trick . Still my goal is to get this thing back little by little to the print . Thanks for any help . I would really like some normal coil ohms date if it is out there? Thanks !
Bill
RE: Philco 70 tuning backward? - morzh - 10-08-2016
I don't have the coil data, we still have no access to the site's schematics and the Rider's does not show the Ohms.
Maybe someone has them locally.
The IF is 260kHz, not 266.
Mike.
RE: Philco 70 tuning backward? - Radioroslyn - 10-08-2016
If you want to hear if everything is work but the LO you can do one of two things. Listen for it in a well calibrated receiver at 260kc above the dial set on the Philco. At the low end of the dial should hear the osc at 810kc and at 1760kc at the high end. You can use a few turns of wire around the 27 tube at a pickup point.
or
You can feed an unmodulated signal from your signal generator at the junction of #6 and #8 though a small cap (size doesn't matter much). Set the generator at 260kc above the frequency of the station you want to receive. Set the radio dial to the station frequency. If all is well (except for the osc) you should be able to tune the whole bcb as long as you keep the generator 260kc above the radio dial setting.
Have Fun!
RE: Philco 70 tuning backward? - sam - 10-08-2016
order chucks prints they are very good
their are a lot of schematic`s for the 70 - 70a below serial #b-22000 and above b-22000
mike
don`t you have them on your computer ? you could had down loaded them
sam
RE: Philco 70 tuning backward? - btoher - 10-08-2016
Thanks to all for responces and sugestions!I am just getting back from a day running around visiting my kid and doing that sort of stuff. But also pondering this. I will take my time and try out the suggestions I have.Did not think of any of them especially since I hit a wall mentally yesterday.First I will go back and check my signal generator against a second one for some agreement. I will put the original mica of .00042 back in and go through all the suggestions. I think Chucks prints are a good idea. The few I have purchased from him were worth it!This could be a coil that was spliced. Or the fact that the componets around it are not correct and it just cuts out .The signal feed will provide some clues. Anyway I feel recharged and redirected so thanks for that!!! I will get back after
I try some of this!
Bilk
RE: Philco 70 tuning backward? - btoher - 10-09-2016
(10-08-2016, 08:29 AM)morzh Wrote: Oscillator backwards (even if worked) has nothing to do with it, as no matter how it oscillates and for what reason, the tuning cap meshing will decrease the frequency and unmeshing will increase it.
You are likely badly out of alignment.
Plus might be seeing images.
Put the oscillator back as it originally was, make sure it does oscillate, and align the radio.
Morzh, I put the original mica back in.Fairly similar but cuts out around 900 instead of 850 .Still have backward stations the same and a 1230 station strong local at 950 on the dial. I did some of the test that Roslyn suggested looking at a scope putting in 260khz between coil #6 & 8 .Am740 came in at1000 and 950 at 1200 a little higher at 960 the strong local 1230 came in. If I park the tuning gang low at Say 740am and hook the signal generator to the antenna and ground I can dial in many stations by changing the freq .Also get harmonics so same station at different frequency. I do not think the micas are original They are areovox and a different shape as others.The coilor code is yellow orange but since I am not sure that relates to the .00042 of the original print .I am not sure they are wrong.So I am pretty certain this oscillator cuts out at 900 two different tubes . Going the chuck route if the 110_pf micas I have coming do not change things. I am not beyond waiting for another chassis on this one. But I also want to figure it out. I think this points to the oscillator and maytmaytbe more. Thanks again to both you And others who helped so far!!!
Bill
RE: Philco 70 tuning backward? - morzh - 10-09-2016
Bill
Again. You need to align tbe radio. I don't see you having done it so far.
If your oscillator is working, as it seems, take the alignment procedure, align the radio.
Then we will know what you are seeing and why.
RE: Philco 70 tuning backward? - btoher - 10-09-2016
(10-09-2016, 08:12 PM)morzh Wrote: Bill
Again. You need to align tbe radio. I don't see you having done it so far.
If your oscillator is working, as it seems, take the alignment procedure, align the radio.
Then we will know what you are seeing and why.
Morzh , I did'nt go into detail but I did align it . Using a vintage Eico and also a modern signal generator .Both agree reasonably. The 260 kHz is alignable but I sense as you alluded
I might not be getting it right. The digital model turns down better and is more controllable output level wise.But this part of the alignment is too easily overdriven (loud) compared to the other radios I have rebuilt and align .Then the lo end 600 of the dial does not come through loud on the next part of the alignment .So you are correct .I am not sure if I am getting it wrong and that is creating my problem. But even though I am not an expert I have done a few alignments and usually they are easier than this. That usually says something is wrong .So set up at first detector grid with dial at 55 input 260 kc remove grid clip that is what I did . If anything i got a strong loud outcome.But not what I would call normal . To strong if anything! Is it possible the oscillator is not even running while I did this?It could be me still.I believe simply that I do not know yet. 1400 aligns ok but with suspect tones down dial 600 Is very weak.Crank up the signal generator just to hear it. So I did algin it but maybe not correctly.Then again it does not want to be cooperative. I think that all the values xc xl r have to be correct for the oscillator circuit to resonate over the full range . Will go back at it again and try .Ordered prints from Chuck .Normally this thing would be done by now! Thanks!!!
Bill
RE: Philco 70 tuning backward? - Radioroslyn - 10-09-2016
If you can measure the output of the oscillator like with a scope and it's pretty uniform across the dial it maybe a problem with the tracking of the rf stage rather than the oscillator. Just a thought.
RE: Philco 70 tuning backward? - btoher - 10-14-2016
(10-09-2016, 11:53 PM)Radioroslyn Wrote: If you can measure the output of the oscillator like with a scope and it's pretty uniform across the dial it maybe a problem with the tracking of the rf stage rather than the oscillator. Just a thought.
Terry, All: I am just getting back to this for a few minutes. I have prints coming and micas also. I can't believe I did all this with the huge tube shield off! That was that cause of the backward dial .Just rf going right around the tuning gang ? Well putting the shield on stops that as well as just about every other station from coming in.In fact just putting my hand near the 1st detector ,oscillator or Rf tube stops all but one strong local station . I do not have much time to mess with it now .Though I would post the ohms on the coils as I think they are
Rf coil primary 7.8 sec 4.8
Coil#6 primary 17 sec 4
Coil 8 primary .7 secondary 5 and 2 oscillator
Coil19 primary 28 sec 28
Coil22 primary 75 sec 53
Not sure where I am going with this .But it has to work with the shield in place. But I may have mislead everyone (including myself ) with the description of symptoms because of this.
Some of the other checks I have done are the voltage checks
But I think I need to go back and double check. Coil #6 with a secondary of 4 ohms seems wrong.
But realize that this check mainly shows things are connected. I had these coils out to inspect ans make sure nothing else was influencing my readings . And it looks like coil #6 had been "fixed" with a larger wire soldered up from the terminal to the beginning of the outside or secondary coil .However this may have been just to get rid of the rot that occurs which many here talk of . It does not appear to have been unwound .Coil 19 and 20 seem to have reasonable values .I would expect a 1 to 1 relationship at coil six .But ohms do not directly tell that story .One coil is wrapped around the outside of the other .Again this may all be fine ?
RE: Philco 70 tuning backward? - btoher - 10-16-2016
update : I changed the oscillator mica to the proper 110 pf . And that did not change the problem . It is as if no rf and oscillator freq is going across this transformer(#6) . But is going cap to cap on the tubes .And that is why it stops when I put the shield on . I think .
Double checked the 1st detector coil (#6) and 17 ohms primary and 4.6 secondary ohms seems incorrect. Does anyone know what this should be ? I am thinking it should be close to 1:1 ratio. I may have that information coming with prints I ordered . But most of the ones I have spare check close to 1:1 ohms .
The only coils I have to substitute are 455 khz peak . So that is where I am at with it .At least eliminating
some things .Thanks!
Bill
RE: Philco 70 tuning backward? - Radioroslyn - 10-16-2016
Check ur pm box.
RE: Philco 70 tuning backward? - btoher - 10-17-2016
(10-16-2016, 02:06 PM)Radioroslyn Wrote: Check ur pm box.
Terry and all
o you see what I see on the last gang ?Wow is that bad to not notice this !!! The person that sold me this should have not let me work on it ! I can not believe that I did this . Or that I now admit it ! But everything is now working properly even with the shield in place. I am happy that all worked out here . Thanks to everyone for keeping me going with good advice . I could not see this easily when the gang was together . I should have noticed before it I did it .Or looked closer when i noticed the shaft being worn .Well this was a first for me and i hope a last . Thanks to all !!!
Bill