Model 14 Sensitivity - Printable Version
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Model 14 Sensitivity - rfeenstra - 11-25-2017
Now that my model 14 chassis is up and running and aligned as best I know how, I've been enjoying Searching the BC band for program material. I have noticed that the low end of the the band is noticeably less sensitive than the upper end of the band. Is this an antenna issue or are there adjustments that will help? I've not been able to test tubes or substitute others as yet. Could it be a tube issue?
Thanks to all of you gurus for your past help. Been having fun with this new "hobby". I've also been playing with a 1941 Majestic 3C70 and have it working quite good. I need to do some alignment on it but as of right now, it is far more sensitive on the low end than the 14.
RE: Model 14 Sensitivity - morzh - 11-25-2017
Obviously if you were able to put the signal through the radio, the coils should be Ok. The 78 tube - you could try to change it, but not likely it is the culprit. Assuming you did in fact put the signal via the antenna input and were able to peak it by the antenna xfmr trimmer.
If the assumption is correct, it is likely the antenna itself. Try a different one, or reorient theexisting if it is directional.
Also if the proper stations appear at their respective frequencies at the lower dial part, the oscillator is tracking properly.
So if you told us everytning, my vote is for the antenna.
RE: Model 14 Sensitivity - rfeenstra - 11-25-2017
The stations are in the correct location on the dial (at least relatively close) My favorite station is at 1300khz and I have that exact. I also used the signal generator to set 600khz. In between and beyond can be off a bit, but not too bad. When setting the 600khz, the signal generator was set up with nothing more than a wire as an antenna and the signal was picked up by the radio via a short wire on the antenna clip. IF was set at exactly 175 khz as required.
The primary of the antenna coil (the part that is on the outside of the form) and the RF amp coil were open. The 38 gauge wire had disintegrated in several locations so I had to rewind them. I understand this is not an uncommon phenomenon on Philco radios. I was as careful as I know how in counting the windings and setting the new wire in the same location as neatly as possible. Is it possible that an error in the winding of these coils could cause the situation? Understand that stations do come in down there, they are just noticeably weaker than on the upper end of the dial.
RE: Model 14 Sensitivity - morzh - 11-25-2017
Well, now that you've said that you did not directly connect the generator to the antenna but used it as a transmitter, it is possible to consider scenario where your 1st RF is somehow bad but the grid cap wire of the pentagrid (the 6A7) acts as the antenna. It will still work, and the strong stations will make you think that the 1st RF is OK too.
Try algnment with direct coupling.
Or, when receving stations, disconnect the antenna and touch the antenna terminal with your finger, and see if the radio reacts.
RE: Model 14 Sensitivity - rfeenstra - 11-25-2017
The RF section is definitely working. I can pick up distant stations from mid to upper end of the dial. If I remove the grid cap on the RF tube, I loose almost everything. I'm going to extend the wire antenna and see what happens. I may also try a different ground rather than the house wiring.
Also, I'm missing 3 of the 4 tube shields. Do they figure strongly in the alignment of the radio?
I really appreciate your input!
RE: Model 14 Sensitivity - morzh - 11-25-2017
When you remove the grid cap from the RF tube, does putiing your finger on the cap restore reception? The grid wire itself is an antenna. The Rf Section and n your case might be working, but what you have told so far does not prove it.
Only successful putting the signal through the antenna connector proves it.
RE: Model 14 Sensitivity - rfeenstra - 11-25-2017
Removing the antenna from the antenna clip virtually kills reception. As I bring my finger closer to the clip without touching it, the stronger stations come in. I'm sure the RF section is working.
Now for an update. I have lengthened the single wire antenna to about 50 ft outside from the 10' to 15' in the basement. The difference on the low end of the band was dramatic. Sensitivity and the number of stations I could pull in down there greatly increased. I think that was the main problem. I'm so used to the short antennas on modern AM car radios and the loop antennas on the typical AA5 that I didn't realize how dependent these early radios are on the long wire antenna that is so often talked about in the literature. Perhaps the long antenna not only helps with bringing in stations but is also part of the tuning for the RF coil, especially in the longer wavelengths???? I'm ignorant in some of this and rely on the expertise of you veterans! Sure is fun playing with this vintage stuff. Now to start the 96. It'll be interesting to see how a TRF compares to a superhet.
RE: Model 14 Sensitivity - Steve Davis - 11-26-2017
When you did the alignment, did you "rock the dial" while adjusting the low end? The idea is to get strongest signal, not to get the dial spot on.
Steve
RE: Model 14 Sensitivity - rfeenstra - 11-26-2017
interesting! No I didn't. Now that you say that, I remember some references to rocking the dial a couple of degrees or so. right now I'm quite satisfied with the performance, bit I think I will adjust the low end of the dial again keeping that in mind. While 600khz and 1300khz are right on, the middle of the dial is about 15 to 20 khz off. Certainly not a concern. I'll try to reset the low end and see if the middle comes closer. I really don't want to start tweaking the tuning capacitor by bending plates to try to zero everything in ( if that is what it would take.) Right now, with the extended antenna, I'm quite happy with the results. The problem is locating the antenna into a permanent installation.
RE: Model 14 Sensitivity - Kenneth F. Besso Jr. - 11-26-2017
Have this little Emerson,,,was picking my brain with,,,,and it turned ---out---that it needed a ground to the cold water pipe,,,and man did it start playing then,,,,CHEERS