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! - Pithicus999 - 01-02-2014
I did have to fix the antenna coil about 6 months ago, and once I did I was able to hear sound. About the 20 foot long antenna, does anyone know what the Philco company used back in 1936 when they made this radio? I don't think my grandparents had a 20 foot antenna, but maybe they did. They could of had it wired out to one on the outside of the house I guess, it just doesn't sound familiar to me that's all.
What about the shadow meter? I believe it's fried as there is no shadow at all when I turn the dial. I'm thinking since the shadow meter is part of the overall circuit fixing the meter may solve the problem?
RE: Philco model 18 (code 121) - HELP! - jerryhawthorne - 01-03-2014
Pith, I can't pick up schematic of the radio. If you can post it. Yes, the meter is part of the B+ that goes to the plate of the front end. Some radios have a by pass with a resistor that parallels it so if the coil opens the radio will still work. Some don't.
jerry
RE: Philco model 18 (code 121) - HELP! - hsusmann - 01-03-2014
Pithicus999:
About the shadow meter. If you have no light showing through
then it either means the light bulb is bad right behind the meter
or the flapper vane is stuck. On my radio here when there is no shadow it means
that max current is going through the coil and is pinning the flapper
to one side.
Thus, if the flapper is not simply stuck, it probably means the coil
is good. It is easy to ohm out the coil to answer that question.
On mine, a spider had built a nest inside the meter and there were
all these spider webs in there pinning the vane down so it couldn't move.
I was able to clean it out with a wire poking both from front and back.
Re: the length of antenna needed. If you want to pick up the weak
stations you will need a fairly long antenna (20+ ft). If you have
a couple of strong nearby stations then you can get by with a shorter
antenna. Getting the far end of the wire up high will also help with
the weaker stations. I have mine on a 200 ft or so wire going up into
a tree.
Herb S.
RE: Philco model 18 (code 121) - HELP! - Pithicus999 - 01-03-2014
Hi Jerry, I have trouble getting a link for the schematic but there's a pic of schematic on post #108.
Herb, I'll check the bulb. Other than that, do you think the reason that the volume increases is antenna driven? I mean, it was just a guess when I put my finger on the tube in the video that the volume increased was due to me being a surrogate antenna!
RE: Philco model 18 (code 121) - HELP! - hsusmann - 01-03-2014
Yes, it sure looks like by putting your finger on the grid cap your body
was acting like an antenna. This is a common phenomenon.
I think you have something wrong between the antenna terminal and the grid of that tube, perhaps an open coil?
Herb S.
RE: Philco model 18 (code 121) - HELP! - Pithicus999 - 01-03-2014
Ok, supposing you’re right and it’s an open coil (although I re-wired the antenna coil item #3 on schematic but maybe something came loose) While I’m checking, I might as well check all 3 coils, can you please take a look at the schematic and verify my plan to check them? I’m not the best at doing this when it involves several connections at one point.
• To check the #3 The Antenna transformer, can I check the resistance using one lead on the G1 of the #78 R.F. Tube and the other lead on near end of the #4 resistor (70 K resistor)?
• To check the #10 The Detector transformer, can I check the resistance using one lead on the grid-cap G4 of the 6A7 Tube and the other lead on the left end of the #13 resistor (2 Meg resistor)?
• To check the #16 The Oscillator transformer, can I check the resistance using one lead on the grid-cap G1 of the 6A7 Tube and the other lead on the right end of the #14 resistor (50 K resistor) or the left side of the #19 Cap (.0001)? This one looks more difficult to read because the circuit comes back into the 6A7 Tube in both paths.
Anyways, if the above examples work for checking the “primaries” of these coils, I think I can use the same logic to test the “secondary’s” too.
Thanks.
RE: Philco model 18 (code 121) - HELP! - hsusmann - 01-03-2014
I am having trouble locating the schematic for this radio.
Someone said it was at post #108 but I did not find it
there either.
If you can tell me how to get to the schematic I would be
happy to look it over for you.
Thanks,
Herb S.
RE: Philco model 18 (code 121) - HELP! - Pithicus999 - 01-03-2014
Hi Herb, you can check back to post #108 in this thread..it should be a picture Jerry posted.
or try here: http://www.nostalgiaair.org/PagesByModel/149/M0013149.pdf
The only problem is that this link is for the 124 version and I have the 121 version...so, there's some differences.
Or I can e-mail you the PDF I can't seem to load it to snapfish unless it's a picture unfortunatley. and it would let me save as a jpg.
RE: Philco model 18 (code 121) - HELP! - hsusmann - 01-03-2014
OK, now I found the schematic (via your link to Nostalgia Air)
the copy in post 108 is way too low resolution to see anything
on the schematics.
Now I have a question, which tube's grid cap were you touching
with your finger to get the volume to come up?
Was it the 78 RF amp tube's or the 6A7's control grid?
This will tell us what area of the circuit to start looking at.
I will be back later today to check for replies...
Herb S
RE: Philco model 18 (code 121) - HELP! - jerryhawthorne - 01-03-2014
Pith, I take the simple approach for testing coils. Check the schematic and the coil base. In some cases the coil also goes out the top to a grid cap. Hook the meter on the grid cap and check underneath to make certain you have a low resistance reading on at least one of the terminals. I then mark that terminal or terminals with a black sharpie. That will leave some other terminals underneath. Clip your meter on one of them and check the others, need low resistance between others. Black mark those. You should end up with them all marked as having low resistance to one or the other.
Perhaps if all check out well when you did the rewind you might have reversed the wiring on that winding. If you have good resistance you may want to try to move the wires going into the coil and reverse them.
Hang in there. Jerry
RE: Philco model 18 (code 121) - HELP! - Pithicus999 - 01-04-2014
Herb I was touching the 6A7 tube.
Jerry, 2 of these 3 actually do go to the grid caps (#3 and #10) so I’ll check for low resistance on those, thanks for the tip. For the one that doesn’t go to a grid cap (#16) I’ll just check from the corresponding tube pins to the other end of the coil (so that I’m checking across the coil that is)
RE: Philco model 18 (code 121) - HELP! - hsusmann - 01-04-2014
OK, so if you touch the grid cap to the RF amp (#78 ) does it
also bring in the signal?
If the answer is yes then the problem is somewhere between
the grid of the 78 and the antenna terminal
If the answer is no then the problem is somewhere between
the 78 tube and the 6A7 grid.
Could be any number of things, open coil being one of
the possibilities. Could also be a missing or broken wire,
a bad connection, a bad capacitor, to name a few.
You're going to just have to start eliminating possibilities
one at a time
Herb
RE: Philco model 18 (code 121) - HELP! - Pithicus999 - 01-05-2014
2 wires on the antenna transformer were reversed, so I switched them back and the signal was much stronger. When I put my finger on the #6A7 tube the volume increased slightly so I figured there may still be an issue. It looks like the shadow meter is sporadic. I removed the shadow meter to test the coil and it seemed to work fine. I hooked the 2 ends to a 9 volt battery and the needle turned fine, and no loose or broken wires.
Then I put it back together and turned on the radio. After waiting for the radio to warm up I turned the dial to see the shadow meter working fine, but then after about ½ hr I switched the channel and the shadow meter didn’t move at all. I went through the entire cycle of stations and the shadow meter didn’t move at all. So I’m thinking that maybe the electromagnet’s wires in the shadow meter are just old and should be replaced?
If that’s the case I don’t know if I can buy one? Or maybe re-wire it?
RE: Philco model 18 (code 121) - HELP! - hsusmann - 01-05-2014
Sounds to me like the vane is just getting stuck inside.
Mine still sticks a little bit but it's not too bad.
I think Brenda suggested recently to spray some WD-40 in
there and try to clean it out and lube it up a bit.
Of course, do this with the power OFF!
Herb S.
RE: Philco model 18 (code 121) - HELP! - hsusmann - 01-05-2014
As for your reversing the ant wires, could it be you had
a primary wire swapped with a secondary wire?
That would clearly cause a problem.
Simply reversing the polarity of either the primary or secondary
should not have any effect, unless there are other parts involved
that I am not aware of.
If you don't have a very long antenna (you had said 4 ft ??) then
I can believe that touching the 6A7 grid cap would still increase
the volume as your antenna is too short to be very effective
at Broadcast band frequencies.
Keep in mind that one wavelength at 1000 kHz is 300 meters so
you need to have some length to that antenna wire!
Herb S.