Model 39-70 stations there, but dial off - Printable Version
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+--- Thread: Model 39-70 stations there, but dial off (/showthread.php?tid=17699)
Model 39-70 stations there, but dial off - NostalgiaRadioTime - 12-26-2017
https://www.tubesandmore.com/sites/default/files/schematics/philco_radio_television_corp_39_70_pg10-1.png
Haven't gotten to the power supply yet on this. Have been battling a stubborn chassis.
As mentioned in the thread about adding an A supply to a B power supply, I found the primary of the OSC coil was open. I replaced it with one of the P-70-OSC coils from the Antique Radio Supply but I could not pull in stations. I then found a winding open on the ANT coil as well, so I replaced that with the P-70-A coil from AES. It receives stations now but the bandwidth is quite a bit off. I get 620 AM with the rotor about half way out of the stator on the tuning capacitor, when it should only be out about an 1/4 at most. I tried aligning it but was only able to move the station back a short way before I ran out of screw (the adjusting screw on the tuning cap is backed out all the way). I can get our other strong local station at 1470 and that seems pretty close to where it should be.
Is it just that that replacement OSC coil may not be close enough to the resistance values / number of windings on the original coil to be compatible? Does anyone have any ideas on what I can try doing to move the lower end of the dial back to where it should be?
RE: Model 39-70 stations there, but dial off - Radioroslyn - 12-26-2017
In the center of your osc coil there is a hex shaped hole use a plastic alignment tool or the proper allen key to turn this adjusting slug. If you use a metal allen key it will change the adjustment a little as the metal will increase the inductance of the coil when inserted.
Use this adjustment to set the low end of the band (550kc or so) and use the trimmer (the screw thingie) to set the high end (1500kc or so).
RE: Model 39-70 stations there, but dial off - NostalgiaRadioTime - 12-26-2017
That did it! I never even noticed that allen head set screw inside there. Thanks!
RE: Model 39-70 stations there, but dial off - Radioroslyn - 12-26-2017
It's easy when you know how!!
General rule. Adjust inductors (coils) for the lower frequency and the trimmer caps for the high end of the dial. This goes for the osc and mixer/rf coils.