The PHILCO Phorum
Modern troubles again - Printable Version

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RE: Modern troubles again - EdHolland - 10-27-2020

This poor thing is still on my bench. Scouring the planet, I found the correct replacement filters from a source in Australia! These have now crossed the Pacific, and I hope to work on the circuit board this weekend.

After that, I want to dig in to something with valves again Icon_smile

RE: Modern troubles again - EdHolland - 11-01-2020

Well these filters are confusing. After being certain I had the correct bandwidth, the replacements are far too wide. It is confusing because the original part number, specc'd 6 kHz is barely if at all traceable. Then the question is that 6 kHz audio bandwidth (for use in AM mode) or total bandwidth. So I purchased filters with spec +/-6 kHz or 12 kHz total bandwidth. They work well in the set, and are properly centered at 455 kHz but are obviously wide. It seems I should have bought components with +/- 3 kHz. Without much expectation, I looked closer at the very blurry schematic in the service manual, this has a part number that is different to the code on the actual filter case, and the required spec is obviousl. Now a replacement is on order, so more waiting... but it should be right.

RE: Modern troubles again - EdHolland - 11-02-2020

Here is the patient. Sorry there are no valves or big tuning condensers. However, in my opinion, this stuff is also gaining classic status, and they really don't make sets like this any longer.

   

RE: Modern troubles again - EdHolland - 11-02-2020

And the problem filter:

   

RE: Modern troubles again - Paul Philco322 - 11-02-2020

I have a friend who is fond of his Frog, FRG.

They are classic.

Paul

RE: Modern troubles again - EdHolland - 11-19-2020

A new (correct bandwidth) filter is awaiting installation this weekend. I hope to get the covers back on and take this lovely radio for a dial spin.

RE: Modern troubles again - EdHolland - 11-23-2020

Success! (at last).

The frog is back together and receiving well. The AM wide reception now sounds correct when the radio is tuned exactly on frequency. Beforehand, it sounded slightly mis-tuned, and the peak indication of tuning was also off frequency. In the narrow setting, with the IF routed through a different filter, everything was spot on.

I've seen this problem a couple of times before. The most severe case, and the first I had seen, was in a receiver that was very much top of the line when they were new. In that radio, the filter was the first in the 455 kHz IF chain, always in circuit and was so far off center frequency - by about 9 kHz - that nothing sounded right. The misalignment also knocked sensitivity right down when using the narrow filters for USB/LSB/CW. Since I had never seen a fault like this before, it took some detective work to figure out what was going on. Even though it didn't put the receiver back to full spec. until I found a replacement filter, it was very rewarding to know the trouble had been isolated when temporary substitution with a resistor as a test brought the set back to life. A new filter completed the job Icon_smile This was a radio I had never expected to own, and thinking back to being a teenager, certainly one I had never expected to diagnose and repair!