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Philco 39-30 Code 121 Push Buttons - Problem Found! - Printable Version

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Philco 39-30 Code 121 Push Buttons - Problem Found! - NV3G - 04-03-2014

I am presently working on a Philco 39-30 Code 121. The broadcast band and short wave band are working nicely. The push buttons do not work. I have taken an oscilloscope and looked at Pin 5 of the 6A8 and I get signals on all eight pushbuttons. I have not changed the 370 uuf capacitors yet.

Suggestions would be greatly appreciated.

Thank you,
nv3g
Oscar

RE: Philco 39-30 Code 121 Push Buttons - Raleigh - 04-03-2014

Pin 5 is the grid of the oscillator section of the 6A8. The RF from the antenna goes to the grid cap. What kind of signal do you see on pin 5?

I'd guess the most likely culprit is either the band switch or one of the push button switches. If none of the push buttons work, I'd suspect the band switch. You could clean the switches with contact cleaner before you do further tests, just to see.

A simple test will determine if your local oscillator is working when in push-button mode. You can do this easily with another radio placed very near your 39-30. Turn both radios on. First, experiment with the 39-30 set to dial tuning on broadcast band. Tune the test radio to a station high up on the dial, say around 1500. Your IF is 470 KHz, so then tune the 39-30 470 KHz lower than the test radio, to around 1030 KHz. The test radio should begin to squeal. (It also might squeal at other frequencies, even when the two radios are at the same frequency. Depends on the test radio, but any squeal of the test radio means your 39-30 local oscillator is working.)

Then try the same thing using one of the push buttons. Since you don't know the frequency the push button oscillator is tuned for, this time tune the test radio up and down the dial until the test radio either squeals or it doesn't. Then check each push button in turn. If no squeals then the local oscillator of the 39-30 isn't working in push button mode.

If no squeals, check continuity of the push button coils. That should be easy. Then check continuity from pin 5 of the 6A8 to the high side of resistor 9. Resistance should be about the same as the resistance of the coils. If no continuity or much higher resistance, then the band switch or the push button switches are dirty or bad. Also check resistor #9. I don't think the push buttons will oscillate without #9 being somewhere near its rated 51K ohms.

If your LO is working but you still can't tune any stations with push buttons, then check continuity from the grid cap to the high side of the antenna trimmers with the push buttons pushed in. There shouldn't be much resistance. If high resistance, then the push button switch or the band switch is dirty or bad.

If you have good continuity through the switches, then suspect those 370 pf micas. There's not much else in the push-button circuit to go bad, if I'm reading the schematic right. (I might not be.)

P.S. You might check the continuity of the antenna coil, but I THINK if both BC and SW bands work, then all parts of the antenna coil are good.

RE: Philco 39-30 Code 121 Push Buttons - NV3G - 04-03-2014

John

Thank you for the excellent reply. I have checked most of your suggestions but not all of them. I will go step by step and check everything you have suggested.

Thank you and best wishes,
Oscar Ramsey

RE: Philco 39-30 Code 121 Push Buttons -Problem Found - NV3G - 04-04-2014

John Honeycutt

Thank you. Four of the 8 switches were NOT working. They would connect when you pushed the appropriate button, but when you pushed another button they would not disengage and that is why none of the pushbuttons would operate. I have removed the switch bank and unsoldered the coils and variable capacitors. There was a lot of rust in the radio and a friend is going to dip the whole switch bank in some anti-rust solution.

Thank you,
Oscar
nv3g

RE: Philco 39-30 Code 121 Push Buttons - Problem Found! - K7Sparky - 04-04-2014

Make sure the anti-rust solution doesn't leach the silver off the PB contacts if you leave the switch boards riveted to the mechanical assembly.

My PBs were jamming because the old grease had lost all the oil and only had the binder left. Like glue on the op rods.

I used a dental pick. Maybe one of the other PP members has a better solution

RE: Philco 39-30 Code 121 Push Buttons - Problem Found! - codefox1 - 04-05-2014

Well, sometimes WD-40 works with a number of paper towels underneath, followed by a little lithium grease applied sparingly with a toothpick the next day followed by rigerous exercize of the buttons. Good Luck!