Need sub test settings for 7b5/7c5 loctals

[Tubejunke]

I have a Philco model 42-350 which employs a 7B5 loctal tube. I'm not sure of its function in this particular set (no schematic), but the FM band doesn't work, so I wanted to test the tubes. I have older and newer testers and neither recognize the 7B5 or its sub. the 7C5. I wonder if anyone has run into this and knows of another tube that's settings would be similar.

The FM band is some sort of early version that only goes to 99 Mhz, but I should still be able to pick up stations up to that point. Any advice on the tube would be great! Thanks!

[Tubejunke]

I just found out that the FM band on these early Philcos no longer works. I did a little online research and found that somehow the dial goes to 99Mhz, but the radio actually only tunes to 42-50Mhz. Go figure! That must be why one of the push-button presets is marked television, which we no longer receive. Besides that, 42-50Mhz is just below the old channel 2-6 frequency. So, since the shortwave and AM selections work on this set, I was troubleshooting for no reason! I still don't get why the dial reads frequencies that the radio is not capable of receiving.

[wa2ise]

Originally Posted by Tubejunke

I did a little online research and found that somehow the dial goes to 99Mhz, but the radio actually only tunes to 42-50Mhz. Go figure!

That's FM channel 99. The FCC uses channel numbers for the old, and the modern FM broadcast (channels 200 to 300) band, though no one else does.

You might be able to receive some older cordless phones and baby monitors, the ones using 49 or so MHz. Also, I've rigged up cable ready VCRs to convert the modern FM band down to the 42 to 50MHz prewar FM band (tap the IF inside the VCR, between its tuner and IF strip, and feed that to the 42-50MHz FM receiver. Tune the VCR to cable channels 96, connect and antenna to the VCR, and you should be able to get some FM radio stations). More in this thread: http://www.videokarma.org/showthread.php?t=252054

[Tubejunke]

Thanks! That is good and interesting information. Really though, I like to have vintage electronics simply working as they were designed to work. I have so many radios (many of which I wish I could move) that I don't really use a particular one all that regularly. I exercise the ones that work about once a year which seems to keep the capacitors up to par. I just thought at first that the FM wasn't working. Good thing I questioned the whole thing before tearing into circuits. This radio seems like one of those true survivors that I always feel lucky to find. All indications are that it has never been restored with only one tube not being a factory Philco tube. The tube compliment always tells me a lot about old radios and TVs. There is a mild 60hz hum that I will probably fix, but it's not all that bad as is.

[sean]

The 7B5 is the audio output tube. A schematic is here:

http://www.nostalgiaair.org/PagesByM...3/M0013523.pdf

You might be able to pick up some strong local FM stations on your set. I have a '42 Philco console with FM and can receive the local country station at 102.1 and an oldies station 15 miles away at 95.3.

[7"estatdef]

If you poke a round a bit you can find a circuit for a converter to cover part of the old FM100 band down to the FM50 band.
GL
Terry