So I had this radio working a few weeks ago. Thanks to the rain last weekend, I decided to get the Beam Of Light working, too. so I made all the connections and powered it up. The light in the tone arm works good, but the photo cell is dead. That really sucks because I could swear it tested OK about 6 months ago before getting boxed up and put in a closet.
To make matters worse, I checked it again yesterday to do a good, long burn-in, and the radio stopped receiving again. Phono input is OK, just no radio reception.
We're heading up that way in a couple weeks for our twin grandsons' birthday party, and my Mother-In-Law is tired of waiting for the chassis to be back in the cabinet. She really wants GrandDaddy (now 97) to hear his old radio working again. At this point, I'm just feeling like I'll never be done with it.
Does that set have the xxl tubes? I had a problem with those when I first powered up the 42-400. (Dirty contacts) Jiggle them around and wait 10 seconds or so. Also, my reception would go out occasionally , but found if I rocked the 7a4 tube, reception would come back in after about 10-15 seconds. Found that underneath on one of the connectors, it was loose in the housing, making intermittent contact with the pin. Made a wedge (out of a round toothpick) and super glued it in. Hasn't lost reception since.
Yes, this radio has an XXL Converter, which I replaced with a NOS tube last December. It's still good.
I just busted out the signal generator and O-scope. Went to the oscillator plate first- good signal, frequency varies with tuning gang.
Next, I checked the converter plate- nice signal there.
Moving on, plate of the first IF amp- nada, zip, zero.
Checked the grid- nice signal. Looks like a bad 7B7.
This set has two 7B7 IF amps, which makes eliminating faults in the associated circuitry a bit easier by swapping positions. So I swapped them and checked the first IF amp with the other tube in there. Good plate signal and even some reduced volume audio tone coming out of the speaker. Bad tube for sure.
Wow, it's almost like I know what I'm doing.
Ok, it was just dirty pins. A few swipes of 600 grit sandpaper, and it's all better.
NICE!!! Totally awesome!!! Get that baby singing for grandad!!!
This 42-400 has three 7b7's ( of which I had to change one out) in it and 4 if transformers. (I incorrectly assumed that the 1008 was basically the same as the 42-400, but looking at the schematics, I see the differences
).
I looked at the schematic for the 42-400, and I see it has an XXL and a 7A4. That seems odd since they are pretty much the same tube. In fact, my XXL has both numbers on it.
Yes, it has 2 xxl's AND a 7a4. Whenever the radio was turned on and the reception wasn't there, I went straight for the xxl's and the 7a4. Never failed, the problems were always rooted right there, with dirty pins, bad tube or the loose pin receptacle. By the way, Eric T, how does the radio sound, did you get the necessary parts for the BOL, and will it be completed for Grandaddy to enjoy? I'm crossing my fingers for ya!
Thanks, Electro. The radio sounds great.
I won't have the BOL working this time around. It still needs a photocell and an idler. Those parts and the time to work on it are not in the budget right now. This is going to be a crazy busy month for me at work, and my weekends are going to be full up, too.
Maybe I'll get to take a week off to go up and get it running this Christmas. Besides, we don't have any 78 records, anyway.
