The PHILCO Phorum
41-280 alignment - Printable Version

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41-280 alignment - dmaugus - 09-18-2017

I've finished re-capping a 41-280 chassis and replacing out of tolerance resistors. Now I'm working on the alignment. The IF alignment went OK as did the broadcast and police bands. Both of these bands track perfectly across the dial.

The problem is the overseas band. I can peak compensator 17A at 12 mHz but compensator 2 has no effect. The image signal is 910 mHz above the fundamental as per the instructions, but at the same volume (not weaker). Also, the tracking is way off at the lower end of the dial. For example WRMI 9395 comes in at 9500 and the image can be heard at 10410 at the same volume.

I'm beginning to think the overseas oscillator coil may be bad. 

Any thoughts would be appreciated.

Dave

RE: 41-280 alignment - klondike98 - 09-19-2017

Welcome to the Phorum!
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RE: 41-280 alignment - Radioroslyn - 09-19-2017

Hi Dave and welcome,
As a troubleshooting measure I'd loose couple a frequency counter to the oscillator.  Frequency received or dial frequency = oscillator frequency - 455kc.
It's important that the osc is running above the incoming signal rather than below.
Have you check the XXL/7A4 osc tube, it may be weak causing the osc to die out at hf.
GL

RE: 41-280 alignment - Raleigh - 10-03-2017

How do you "loose couple" a frequency counter to the oscillator? Through a .1 uf capacitor to the oscillator plate? I'd like to try this just for fun, and to have a new technique to use for the future.

RE: 41-280 alignment - Radioroslyn - 10-03-2017

Hi John,
I just wrap a few turns of hook up wire around the osc tube. Depending on the circuit you could use a capacitor to couple it but .1 is way too large, this could stop the oscillator from oscillating or dramatically shift it's frequency. The idea of loose coupling is to just couple a small amount of signal with out interfering with oscillator frequency. For capacitance coupling the counter I'd use something on the order of 5-20mmfd. Being kinda lazy I'll grab some wire and make a gimmick cap.