Okay, I'll preface this with the fact that I work at a radio station and noodle around with old radios...but I'm not an engineer by any means. I'm also 32 and have learned a lot about this stuff, but have a LONG way to go. So my '47 Chevy's original radio buzzed and powered up when we got the car, but never played audio. You could hear the vibrator humming and the dial lit up...but that was it. Fast forward to a year later. It was sent to an old timer / club friend of father's who has redone radios in all of our old cars for 25+ years. This gentleman is getting up there in years though and I don't want to keep bothering him. Plus I hope that I can learn some small things and keep the hobby alive. -Long Story Short- The OZ4 rectifier tube was replaced and the rest checked out fine. He marked the good tubes and vibrator as OK and it worked on his bench. Now when we hook it up to 6V power using the original fuse holder it pops the 15 amp fuse its supposed to have. Won't power up. I don't have a tube tester, I don't want to take it back to the guy (it took 6 months last time due to health problems...dude is old) so anyone have any guesses on where to start? I would assume the vibrator is a cheap way to begin...but when I pulled out the 6V6GT tube it felt loose like the seal had blown and had some shiney glass like its burned out. Does anyone have good bench-testing advice without buying $1000 worth of obsolete testers? Should I replace this tube AND the vibrator and go from there? Can I pull out a tube at a time and see it blows a fuse? Would that tell me anything or is it possible? Any advice would be appreciated. I'm trying to revive this old thing and have it working for cruise season. I hate butchered / modern stereos in these old cars and want to preserve what I've got and make it look right.
The high-current mechanical Vibrator is a usual suspect. IF the points in the Vibrator are arc'ed shut, the fuse probably would blow. Try pulling the Vibrator - it should be socketed. The Shiney Glass is nothing more than the "getter" used to flash any residual oxygen in manufacture. If the 6V6 is suspect - swapping is simple test. The Tube's themselves are remarkably tolerant and usually drift off spec rather than - semiconductor type - progreassive total failure. My tube radio in the '50 occasionally has similar problem. When idling, the voltage to the radio can drop to the point where the VIBRATOR stalls and welds the points shut. (with all those tube heaters glowing) I got pretty good at opening the vibrator can and using a Points File getting it buzzing again. There are electronic vibrators INSIDE original looking vibrator can availble through vendors in Hemmings. .
Any chance that there might be some Youtube tech videos?? I don't know anything about those, but I sure do remember that exact tube number from long ago. I agree. I hate digital tuners. A digital tuner decides what station you will get if there are 2 or more stations trying to come in on that AM frequency. It will lock onto the one you hate.. or if both are weaker, it may be silent, as it thinks you would not want to hear less than perfect signals.. I noticed that with an older manual tuner in my shop, that I can tune in my favorite oldies AM station, but if I try a modern radio in the shop, it won't pick up anything on that frequency at all. I don't want any machine to make desions for me
The vibrator is the primary suspect. As said, Shiney Glass ok. Pull the vibrator out and rap it on something. If the points are not stuck too bad sometimes you can shake them loose. They are not sealed and the points can corrode when they are not used often. If it is not buzzing, it is not working.
If the vibrator points have been stuck shut for a while the power transformer can burn up causing the blown fuse even with a good vibrator. Pull all the tubes then see if it blows the fuse if so try a known good vibrator, still blows probably the transformer. I haven't had good luck filing the points on old vibrators and have been installing the new electronic ones. Most tube radios will operate with positive or negative ground. Only transistors care about polarity.
If it blows the fuse, there is an obvious short (probably in the power supply), if you hooked it up with the correct polarity. Pull the tubes and vibrator, if it isn't hard-wired and reconnect. If the fuse still blows, check the wiring and connections for anything lose and touching ground. If the fuse doesn't blow, put the vibrator in first, followed by rectifier OZ4, then power tube 6V6 and remaining preamp tube(s) and fire up between each. Process of elimination will find the cause of the short eventually. Tubes usually don't short to ground to cause a main supply short and the vibrator is the usual suspect.
I agree that it's unlikely that a faulty tube is your problem. The vibrator is a likely suspect, as well as a failed electrolytic filter capacitor in the power supply circuitry. A shorted filter capacitor can be essentially a dead short across the B+ power supply that supplies plate voltage to the tubes, and draw a much higher than normal current to the radio. And those filter capacitors are prone to failure with age.
"So my '47 Chevy's original radio buzzed and powered up when we got the car, but never played audio." OK, so I'm a FNG - sorry - but only GeezersP15 is even CLOSE to be right about getting your radio going. Your 66-year old capacitors are shorted out and you're going to fry something expensive if you keep changing tubes "to see if it will buzz". I recommend you take a look at the forums at antiqueradios.com where we restore tube radios or contact Gary Tayman at Tayman Electrical in Florida. He can make it work like new.
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