37-660 Alignment Issue - Printable Version
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37-660 Alignment Issue - marv - 04-26-2012
Well I've rewound the OT and it works fine. Began the alignment and all was going fine until the last SW tuning range 2 (2.3-7.4 mc). The first part of this stage you peak at 7 mc by adjusting the oscillator (30B)(no problem) and then you are to go to 2.35mc (closing the tuning cap plates) and peak there (30C) where I don't hear the sig gen signal.
If I set the sig gen to 6 mc the radio dial has to be set to about 6.65 mc to hear the tone (this is after peaking at 7 mc). To me it seems like it is short on capacitance. I note that across 30C (the 2.5 mc osc trim) there is what appears to be a large mica. According to the schematic this is 30x and is a 1150 uufd (I didn't change this one). The parts list does not say it is mica whereas it does state other small ones as mica. I am wondering if this cap might not be mica and could be causing my problem? Looking to you experts for help and suggestions.
http://www.nostalgiaair.org/PagesByModel/220/M0013220.pdf
RE: 37-660 Alignment Issue - TA Forbes - 04-26-2012
Hello, Marv: The best way to align is to connect a volt meter to the voice coil leads of your speaker and use min sig gen amplitude when adjusting your set.
This prevents your AVC circuit from interfering with your alignment.
RE: 37-660 Alignment Issue - LASJayhawk - 04-27-2012
If I had to guess (and I do)
you are on the wrong peak. ie if the LO is to be at 6.53MHz when you tune 7Mhz, you have it peaked at 7.47 Mhz on the LOturn the signal generator level down, and try to find a peak at 7MHz with the trimmer turned in tighter.
I would also assume the 1150 pF cap would be paper, you could try putting 2 .0022uF caps in series (1100pF) and see if the situation improves.
RE: 37-660 Alignment Issue - marv - 05-09-2012
Still have problem on range 2. Changed 1150pfd cap, no difference. Close inspection of coils noted that one lead of RF range 2 primary broke off wafer switch. (Probably happend when replacing caps deep within). Soldered lead back on to D3, still cannot align this range correctly.
Before I remove the RF section from chassis again to check this coil closer can someone please confirm that when the radio range lever is in range 2 I should read 12 ohms of the primary between D3 and D6 of the wafer. I read open. Getting to these coils is nearly impossible.
marv