philco: 40-180XF

Hello Fellow Vintage Radio Fans

I am experiencing a problem with a Philco 40-180 that I could use some pointers and tips on to help me solve it.    The radio powers up (still using the old wax paper caps. but will change them soon).   It is very noisy probably due to the old caps and the old cardboard fine tune drum wires losing insulation.   But my problem with this radio is that I get only one station ... it's stuck.   Tuning condenser runs smooth ... with a new cord.   Oiled the bearings.   Band switch works but every band has the same station.  Push buttons do not seem to function.    Essentially, the radio receives only one station and very poorly and with lots of noise.    Where should I look to troubleshoot this problem?

Thank you,

Bill in northern California

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Bill,

you do not say what kind of noise you hear in the speaker. Assuming that it is a hissing or whistling sound, you could have a stage, maybe the RF or the IF amplifier, oscillating. This could explain the poor sensitivity of your set. The oscillation, if present, is rectified by the AGC detector and, just as any strong signal, lowers the gain of the RF and IF stages.

Try to check the grid voltage on the RF amplifier, the 1632 / 7G7. In normal conditions you should find about -2V. If you find a more negative voltage, say -4 to -8V, probably you have an oscillation somewhere.

Emilio

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Hello Emilio

Thank you for your reply.   The noise is mostly static ... as I change the band settings the one station signal I receive is either louder or fainter ... but always there is static ... I'm wondering if it might be poor insulation on the fine tunind drum wires.   Missing insulation is some cases.    Just old and brittle.   But my main question remains ... why is the radio "stuck" on one station?    When I use the tuner and when I push the buttons.    Very odd.

Many thanks again Emilio

- Bill

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Well, I read too hastily your description of the problem. If you hear only one station, regardless of the position of the band switch or of the tuning control, then the local oscilator of the frequency converter 7J7 is not operating. What you hear is just a strong station entering directly in the IF amplifier.

In this converter tube a triode section is used as local oscillator, cathode to pin 7, grid to 4 and anode to 3. Try to check the anode voltage first. Then you should check the continuity of connections from the said pins to the tuning components, through the band selection switch, item 26 on the diagram.

Emilio

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Missing connection to coil pack and tuning capaictor, likely "common" on switch unit or wire to it?. You need to "sniff" or connect to L.O. (local oscillator) (g2 if a Heptode and triode anode otherwise, I didn't look at schematic). It would seem the L. O. is running at a fixed frequency unless the IF frequency is equal to a Radio Station (very unlikely!).

It's a strange fault. I did have a set with Open Circuit MW coil and it picked up SW R.China every so often all the way across the tuning scale.

Do you have a Scope, Dip Meter (with Wavemeter mode) or a sensitive Frequency counter? Or even a continious coverage receiver and tune it with a 6 turn loop about 4" (10cm) across on aerial & earth in to find the L.O. frequency of your Philco. Then you can see if it changes with tuning.

How do the presets work? Are they electronic (separate tuned circuits) or mechanical moving the same tuning capacitor as manual tuning uses but to preset positions? In such case I suspect a missing connection to Tuning capacitor L.O. Section as the Trimming capacitor will hold it then at the HF end of BC band.

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If you do not have the "Dial" push button pushed your oscillator will not track the variable air cap.  That button is one of the outer buttons (far right I believe). 

Paul P.

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