Hi all:
OK, I'm stumped! Have been working on a 47-1230 console, but the audio is low. Tested and replaced bad tubes, replaced filter caps w/ 33mfd 450v electrolytics (removed ALL trace of hum). Tested all paper caps for leakage - OK. Also tested speaker and choke coil - good. B+ is normal. It would seem as if all stages up 'til final audio (PP 6V6) are in good order - sound is clear up 'til 3/4 volume or so, then gets a little clipping distortion. The audio finals test just above 'OK', but hot hi-scale on my eico 666, near other known good 6v6s - same w/ 5Y3. Output xfrmr tests good per ohms in schematic. Thanks a million in advance for suggestions! Have a good one,
PS - I originally posted this in the section 'Philco home radio', having meant to post it here. Only took me 3 days to figure that out. I am, of course, an idiot!
Have you checked the bias in the output stage? I would also replace the coupling caps in that stage, and if there is a small capacitor across the primary of the output transformer, I would replace it too. You pretty much have to take these components out of circuit to test, and it's cheap and easy to just put new ones in. And clean the volume control too. If that doesn't do it make sure the problem is not before the output stage by tracing the audio with another amplifier. Could also be a problem with the phase inverter circuit or tube. I don't have the schematic in front of me, but that's the course I would follow. Good Luck.
You can go to
http://www.nostalgiaair.org , look up the Philco 47-1230. You can download those pages to your computer. Page 5 gives a detailed troubleshooting guide for the audio section of your radio.
Hope this helps.
nv3g
Oscar
Thanks!
Now, for a few hours to dig in... I suspected it might be an issue w/ one or more defective components, but I'm still 'cutting teeth' at the old radio game - updates to follow.
YEE HAW!!
OK, now there's audio! Many thanks for all of the help. I figured it'd be just as easy to replace all the coupling caps in 1st and 2nd audio stages, rather than testing them all first - plus, it might avoid headaches later on. I used ceramic type rated 3 kv - I hope they're OK for this application. I found correct values for the .003 mf, but was unable to find .006 mf - I don't think that's a standard value now - used .005 instead. I hope that's OK. At any rate, next step is an alignment, but I can see light at the end of the tunnel (it's not a train). Thanks a million!
You're doing fine. Ceramic caps are OK, unless you are an Audiophile who wants gold foil caps immersed in virgin olive oil sealed in optical glass with silver leads. After all it is only a radio. Let's not go there.
You should also replace all the other ancient wax capacitors in the set too, as they will without doubt be leaky and way over tolerance before you do the alignment. Try to stay within 20% of the prescribed capacitance. While you are at it, measure and replace all resistors that are out of spec. All carbon resistors of yesteryear drift up in value ; replace them when they are more than 25% high. Or just replace them period. They ought to be costing you a dime or less per.
Don't replace he mica ones unless they are way out of line when tested out of line with the expected voltage applied to them. The little bitsy ones in the IF cans can fail at 12 volts DC, yet appear to have infinite resistance. Been there, done that.
After you are finished, align the set, and let us know how you are doing
OK - alignment done! Touchy, touchy, touchy! I have done alignments on some ham gear before, w/ slug-tuned IF xfrmrs. They're much more forgiving. Anyway, AM and SW are just fine, but the closest I can get FM is about 1 mhz away from correct dial reading, but no big deal. Surely it's some out-of-value component, but I decided to pass - they're like sardines in that sub-chassis, where I assume most of the FM circuitry is. Returned it to its owner this morning, and can resume sleeping in bed again! Thanks for the help,