C23 is problematic for me for a couple of reasons, so...
Photos of the chassis I can find online had the same problem the one I have had which is the .1uf cap in C23 was replaced outside of the Bakelite box and R24 may or may not be there. At any rate, i have two questions:
the placement of R24 and the placement of leads going to the 78 tube cathode, IF 27 primary, and grounding of the .01 cap and R24.
Is my diagram correct? There doesn't seem to be a lead for the ground of the .1uf cap and R24 in the set, and C23 isn't a grounded Bakelite cap, either, so I was left scratching my head.
I tried it out and the radio works...in a manner of speaking. I can tune broadcast signals from different stations on different parts of the dial, but the volume is quite low. I suppose the good news is the antenna, IF, and oscillator coils are all good (verified by DMM measurements as well). FC measures at 1200 ohms, but should be 1000 ohms. Is that a problem? The OT measures 400 as it should.
I'm using about 15' of wire for an antenna and I have a ground, so almost certainly I have an output stage issue, right? I'm considering pulling the volume pot and dismantling it for a good clean up. It turns with more effort than I'm used to, but the switch works. It measures at 500K. I have another 500K volume/on-off switch around here somewhere, maybe I'll sub it in instead.
On a dim bulb test, a 60 watt bulb goes bright for a second, dims, but has a moderate glow-not bright by any means, but there. I'm trying not to run on direct mains for longer than it takes to verify that I can tune a signal in and that the volume is too low. In fact, not at all unless I have something in the output stage I change that is significant enough to warrant another test.
How crucial to output volume is C32? I'm using some salvaged mica caps there, and I'm not certain about them. I'm also kicking myself because when I dug out the tar on that one the caps turned out to be old-fashioned mica caps, so they were likely still good.
By the way, some past owner put in a home made loop antenna in the cabinet (this is the console model). Is that what the red and black terminals on the back of the chassis are for? The way the antenna posts look on the schematic, it seems like this set would work with a dipole antenna as well, but I'm honestly not all that knowledgeable about antenna issues.
Charlie in San Antonio
(This post was last modified: 09-21-2015, 06:58 PM by ccomer1955.)
I wouldn't necessarily say the problem was in the output stage. Have you aligned it yet? At least do an IF alignment and see if you improve the volume.
I wouldn't think the 110 uuf caps would hurt your volume as long as they are connected right and aren't shorted. You can detect a shorted or a leaky cap pretty easily with an ohm meter.
If your meter measures capacitance you might be able to measure the capacitance to see if it is approximately what it's supposed to be, though the lead capacitance will interfere with your measurement. You can compare with a known good 110 uuf if you have one and see if it's in the same ballpark, or you can short your leads to approximate the lead capacitance and then subtract. If you're suspicious that the two caps are way off, it might be a good enough measurement.
Got it sorted. It was the grid lead on the 42 connected on the wrong side of R46. Amazing that it played at a listenable level hooked up like that. Connected on the correct is, the set plays beautifully. This set seems to be a great little performer: sensitivity is good and the sound seems clear and loud through that little speaker. It easily fills a room with sound.
