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Philco 42-123 - Printable Version

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RE: Philco 42-123 - texan george - 10-13-2021

Finally got thru the radio again and think I have the wiring right. Powered it up and got nothing, no sound or noise of any type. Checked the B+voltage on the tubes and they were in spec. Checked the resistance of the osc coil and it was fine. Tried the 2nd radio test and no squeal anywhere on the dial. I dont know what to do next. Seems like this critter has more aches and pains than I do. Any ideas would be greatly appreciated.
George

RE: Philco 42-123 - mikethedruid - 10-13-2021

Work backwards from the speaker. Start at the audio output tube. Feed an AUDIO signal through a .1 MFD condenser into the junction of C23 and R24 and the control grid of one of the 1LA4 output tubes. If you get sound then work further backwards. Feed the signal in at the plate terminal of the 1LH4 tube. See if it comes through. Then switch to modulated RF at the IF frequency, 455KC, and feed it in through a .001mfd condenser to the terminal of the 1LH4 to which the green wire from the 2nd IF transformer connects. See if that causes the audio to come through. If it does, then go to the control grid terminal of the 1LN5 IF amplifier tube, and feed the same signal in there. If it still comes through, try feeding the signal in at the plate terminal of the 1LA6 pentagrid converter. If it still comes through then your problem is somewhere in the circuitry there around the RF and oscillator circuitry. If it stops anywhere short of there, then look for your problems in the area around where it stops.

RE: Philco 42-123 - texan george - 10-13-2021

Thanks for the reply Mikethedruid, my rf signal generator is not working, no output. I should get it fixed next week. Went back and did more testing. 2nd radio test thought I did get a squeal on the low end of good radio. Osc coil read 8 ohms from 1to 2, 3ohms from 3 to 4. Voltage on 1LA6 were:
Pin 2  78V
Pin 5 40V
Pin 3 78V
Pin 4 -1.78V
Anything else I can do without a sig gen?

RE: Philco 42-123 - RodB - 10-13-2021

You can touch the control grid pin of each of the audio amplifiers with a screwdriver or alligator lead. This will inject a 60 cycle signal to the grid and the speaker should respond with the hum.

RE: Philco 42-123 - texan george - 10-15-2021

RodB, I tried that and got a faint buzz on one of the 1LA4 tubes but not the other one. Must be somewhere on that. I'll keep plugin away. Thanks
George

RE: Philco 42-123 - Radioroslyn - 10-15-2021

On the audio side of things I'm assuming that you've replaced the foil/paper caps. With that done #'s 19,21,and 26 are suspect. An other thing is with loctal tube the pins can get oxidized. Cleaning involves gently scraping the pins with a sharp knife like a snap blade or exacto.

RE: Philco 42-123 - texan george - 10-16-2021

Thanks to yall. Radoroslyn, I did change those. As you know I had to put in a different 2nd IF. The resistance on both sides was 23 ohms, I added a 100pF on both sides. I just cleaned the pins and got a loud squeal. I put in a 220pF where I thought C12 was and got reception on 1330 and  1370 AM but nothing on the lower end. Something to get excited about finally!. Now I really need your help to get this old girl better. Thanks for all yall have done.
George

RE: Philco 42-123 - morzh - 10-16-2021

>>>Cleaning involves gently scraping the pins with a sharp knife like a snap blade or exacto.

There is nothing gentle about it: it has to be really scraped. And because this involves a dull Exacto, the less gently, the better Icon_lol

RE: Philco 42-123 - texan george - 10-24-2021

Still no reception on lower end, could that be due to installing a different IF with fixed values? Should I look for as IF that can be adjusted?
George

RE: Philco 42-123 - MrFixr55 - 10-24-2021

Hi Texan George,

In theory (!!??!), tuning of the IF Stage should have an equal effect across the band, as the Convertor Stage converts all frequencies to the fixed IF frequency.
There could be one or more of several possible issues with the Convertor Stage. The most likely cause of reception at the high end of the band but loss of function as you tune down the band is shorting of the ganged variable tuning condenser. A click or static while the tuner is turned is a dead giveaway. Look carefully to ensure that the plates are not shorting. In addition, if the aluminum corrodes, there are almost thready bristles that will short the condenser out, almost like "SMD" An ohmmeter may be useful but you will have to unsolder the connections. I had this problem with a Crosley 02CA I restored for a friend (BTW, rubber wiring, not for the faint of heart). Take a set of feeler gauges and sweep the gaps between the plates, either open or closed will help. compressed air after this procedure helps.

If the Unit passed the 2nd radio "squeal test" then the Oscillator section of the tuning condenser is OK and the problem is with the RF section.

Hope this helps.

RE: Philco 42-123 - texan george - 10-26-2021

Thanks to MrFixer55,
used the feeler gauge on the tuner and found some tightness, gently spread them and now I get some reception on the lower end. Trying to get this working as best as I can then I can start on the cabinet.
Thanks again,
George