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I've just finished getting the 46-350 working well (had to replace the output transformer), and the problem I have is that it;s working TOO well. I can't get the volume all the way down. It seems to settle somewhere in the mid-range, and I can't completely silence a station. I checked the volume control for shorts and proper values and everything seems in spec. I replaced a couple of out of spec resistors along the way as well with no difference.
I'm not a newbie, but I'm not a pro at this either. Anyone ever have this 'problem'?
Bill
(This post was last modified: 03-12-2013, 03:26 PM by billp.)
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I had a similar problem with one of my ex-wives......
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The output transformer was bad on my 46-350 also. I got a second one and used the original for parts. Where did you get your replacement?
Just on general principles, could the AVC in your radio be open somewhere if you can't bring station volumes down to reasonable levels? I'm definitely not clear on how the AVC works on this radio, but it looks like the AVC voltage is filtered inside the 2nd IF can. It might be that R302, 22K Ohm, which (I think) is inside that can, is open. If not, there might be other resistors in the AVC circuit that are open.
Philco's number for that can is Z301. I'm pretty sure their intention was for you to replace the whole can instead of replacing components, so they don't show the location of the components inside it in their service package, but both the Philco and Rider schematics show that resistor surrounded by a dotted line along with the If transformer coils and other components.
There is also a 2.2 Mohm resisitor R301. I'm probably missing something, but I don't see you can get your AVC voltage without going through those 2 resistors.
John Honeycutt
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Thanks, John, that gives me a direction to look. I didn't consider the AVC.
I bought the output transformer from AES - part# P-TA-8037 (5k primary, 3.2 ohm secondary)
(This post was last modified: 03-13-2013, 07:46 AM by billp.)
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My suggestion would be to check R3, R17 and C20.
If either of the resistors is open, it will affect the ground path for the signal. If the capacitor is open, enough signal might leak through the AVC circuit to drive the 3Q5, though it's difficult to tell for certain.
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I just noticed that Philco and Riders use different component designations. So if you you have the Riders schematic, you'll have different reference numbers. My copy of Riders is almost illegible, so I can't give you corresponding references. Follow the path from the detector diode through the IF can secondary to find the 22K resistor and then to the 2.2 Meg after the split at the volume control.
I saw a reference in Chapter 12 of Marcus and Levy "Elements of Radio Servicing" that looks like it describes your symptoms. If reception is poor because of problems between the antenna and the RF tube, the lowered signal might cause your AFC to act like you're tuned to a weak station all the time, so it'll over boost all stations. Check the 30 mmf mica cap between the ends of the antenna loop. (C1 on my Riders schematic, C400 on the Philco.) There's also a .0015 mF cap (C2 on Riders, C403 on Philco) that you might check out. Also any connection in the loop antenna and its connection to the chassis or to the external antenna connections could create this kind of problem.
John Honeycutt
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Thanks for all the suggestions. I've got a little work ahead of me. I'm trying to fit this in with my honey-do list. I'll keep you guys informed of my progress.
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OK, I've been doing some probing. I got a copy of the Riders schematic, 'cause all I had was the one from Philco, and as you've noted, the component designations are different. BrendaAnn, I found that I'd already replaced R17 and C20, and R3 checked out OK. I started to plan my attack on the 2nd IF can to see if R302 was open. It was going to be a bear to remove the cover, so I thought I'd just take a reading from the 2 wires (coming out of the can)going through that resistor (the white running to the volume control, and the green going to pin 4 of 1U5). I thought if the resistor (R302) was open, I wouldn't get much if any reading. Is my logic correct in this? In any event I got a reading of about 28K, which seemed reasonable (?).
All of the other resistors check out in spec.
So the AVC components seem to be OK. John I'm going to start investigating your other theory of a problem in the RF section.
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Well, everything checks out OK - same problem. I tried swapping out the 1U5 and 3Q5 with no difference. I'm getting ready to align it, but I don't expect that to change anything. I'm wondering if the new output transformer could create this type of problem, if it wasn't quite the same as the old one?
Time flies like an arrow, fruit flies like a banana
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Output transformer does not create this kind of problems. It is a transformer. If the input is 0V AC, the output is N*0V AC which is 0V AC.
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