uhf converters

[Adam]

I rebuilt the power supply on that Philco UHF converter I got, replacing the selenuium rectifier with a 1N4007 diode. Space for the capacitors was tight, but I got everything in there. It works good, and it works on ch 3. So I don't really know now if the reason it works better is just that it works on ch 3 as opposed to 6, or if the extra amplifier tube is really making a difference. Here's pics of it. On the screen picture, the light and dark areas as well as the horiz lines, are in the picture, but not on the set, I tried taking about 20 pics, but they all had that problem.

[Jonathan]

I have the RCA U70 model. Mark Nelson was kind enough to send me the service data for this unit so I recapped it. It only needed 3 electrolytic caps. On this unit, the UHF input was an odd looking female 72 ohm coax connector with a small piece of 72 ohm coax as a feed line to the tuner. Tuner was dual ganged I think. I removed the 72 ohm connector, widened the hole in the bracket the connector was secured on to and installed a 75 ohm F connector and 75 ohm RG 59 to replace the feed line.

I first tried a modern RCA amplified antenna, but like most modern RCA junk, it's crap, despite the high price. So then I tried my old grungy pair of rabbit ears I had and got decent performance, but couldn't tune in anything past channel 38 because channel 44, 54, and 64 I could not tune. The service data says to realign the UHF tuner section, or replace the germanium diode in a case like that. Also, the channels I could tune only came in good if I had the rabbit ears in the right spot. If it wasn't in the right spot it's barely watchable. I used mine on a modern Sony set with digital tuning, and channel 6 it operated on.

I remember with a lot of servicing solutions from the service data, replacing the diode was one of them. Once the diode was replaced you had to realign the UHF section. I'm not sure if the old diodes go bad or what. I think the diode was 1N72. NTE has them, but in a leaded DO-XX case. the older ones had no leads. If you replace it with a modern one you'll need to realign that section, but you really shouldn't have to.

Jonathan

[wa2ise]

I've heard it said that diodes used in microwave work are easily blown. And to never test one of these with an ohmmeter, as that will blow it out. Not sure if the ones in the UHF converters are like this or not...

[Adam]

The philco uhf converter is back in one piece and working.