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Weak reception 42-355 - Printable Version

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Weak reception 42-355 - Raleigh - 09-17-2009

I got the 42-355 back in the cabinet and all aligned. Problem is, the bottom frequency range is very weak compared to the upper, and also compared to other, similar radios. This did not seem to be the case until I put it back into the cabinet, but I'll have to take it back out of the cabinet to be sure I remember correctly.

The reception improves dramatically all across the AM and SW bands when I touch the loop antenna or when I clip my random wire antenna (which I use as a working antenna in my shop) in place of the loop. The low end comes in fine when I do any of these things.

I also get some improved reception in my 41-250 when I touch the loop antenna, which looks identical to the loop on the 42-355, but it isn't as dramatic an improvement. On my 42-350, I get no change at all when I touch the loop.

Because I get better reception when I touch the antenna, I conclude there is something wrong with the antenna circuit. I think maybe I'm changing the antenna impedance when I touch it, so maybe the coil (part 5) is bad? Also, when I turned the antenna compensator (part 6) during alignment I got no change at all. This doesn't seem right, so maybe that compensator is out of the circuit for some reason?

BTW, the push buttons for the low end of the dial get great reception, loud and clear at all times, much better than the dial tuning, which also makes me think the antenna circuit is faulty.

I tried switching out the XXL oscillator and the XXL mixer with several other used and NOS tubes, but it performs the same with all tubes, so the oscillator seems to be OK.

Any thoughts?

Re: Weak reception 42-355 - Chuck Schwark - 09-17-2009

Classic symptom of an open antenna loop or antenna coil in the front end. Check continuity on the AM loop section of the plug-in loop assy and also coils #4 and #5 in the schematic for continuity. Be sure to check the coil taps too. Bandswitch contacts or grundgy bandswx phenolic are also #1 or #2 on the list as well.

Chuck

Re: Weak reception 42-355 - Raleigh - 09-17-2009

Chuck,

Thanks for the pointers. I found an open at pin 4 of the antenna coil (part #5). After I fixed that and repeated the alignment everything on the AM and SW bands seems to work perfectly. There isn't any noticeable difference when I touch the loop antenna.

The coil fix seems to have reduced the FM sensitivity. Before, I was getting five stations all across the band, but now I only get the strongest one. That's OK, because I never expected to pick up modern FM stations on the old pre-war band. Maybe the open coil changed the FM reception in some way. I didn't do the FM alignment because I found the instructions confusing. It says to connect the signal generator to "2nd IF FM input connection." I assume that means the 2nd IF transformer, not tube, but I don't know what the FM input connection is. (Unless maybe it is grid 2 of the 1st 7V7 tube?)

Thanks again. I'm really enjoying this radio.