Confirmation of a no-brainer, Please!
Posts: 147
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Joined: Nov 2005
Ok, This is regarding, of course, the 37-650.(My RF Generator is back online, thanks to some help from friends, and a manual supplied by W7FG.com- Thanks!)
Here goes: When I rebuilt the chassis, I replaced all the original resistors, with new ones from Radio Daze. All seemed well, until tonight. Researching a resistor for a probe rebuild(for my oscilloscope) I happened to notice something did not seem right with some of the left over new resistors. As I had trusted my supplier, I used what was sent, without reading the codes.
I have come to discover that the resistor I used to replace number 46 had the color code: orange-orange-grey-gold. If I am reading this correctly, it is 3,300,000,000 ohms, not the required 330,000 ohms (orange-orange-yellow-gold) called for - about 10,000 times the resistance specified.
First- Am I Correct in this belief;
Second- Could this be the long sought problem with my receiver;
Third, would this have worked as described for a few hours, and then given up? (Described as- low volume on all but very strong local stations, and only moderate volume then)
I am pretty sure it is- This resistor falls between the bias resistor(58 ) and grid 1 on the 6F6G Output tube, also prior to the #45 condensor leading to 6K5G First Audio plate.
I do know one 6F6G went bad: hopefully I haven't destroyed anything...
I am going to attempt a substitution, and see if I get a signal through, but I am looking for independent confirmation of my assessment...
Chuck? Ron? Anyone?
And Yes- I think I will keep it toward the front of my mind to check each resistor next time as they arrive: not just leave it to faith.
Thanks!
Scott
Old Cars, Old Radios, Old Pipes and Young Women... What more is there?
Posts: 147
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Joined: Nov 2005
Ok- I swapped in a temporary patch- I snipped out the wrong resistor, and in its place substituted 3- 100k's and a 33k, with a total resistance of 339(?)k ohms, where it should be 330k. My estimated window is 297-363k ohms, so I should be ok. I now get squak. No stations yet, but that is most likely because everything is out of alignment now, having muckered about with everything I could see to try to get anything out of it. And the good news is, the squakies do very nicely with tuning adjustment, and the volume gets loud and soft now- a marked improvement over what was happening.
I will now attempt to divine the RF generator and its use to align everything. Pay no attention to the man behind the curtain...
This is only on the AM side of the house: I have no SW noise at all. First I want something going, then I'll worry about the details...
Any tips, hints, gladly accepted!
Thanks!
Scott
Old Cars, Old Radios, Old Pipes and Young Women... What more is there?
Posts: 147
Threads: 28
Joined: Nov 2005
Ok- Here's where I'm leaving it tonight  Time for bed- 4 am) I have gotten things roughly adjusted. As I have no real clue what I'm doing, I'm following the directions best I can... While I have no appreciable understanding of a lot of this, I have it to the point is makes squakies and squeals at approximately the right positions that one might assume I am hitting stations, but have not quite gotten things reeled in.
I almost heard something that sounded like voice, but it may have been my imagination.(Does anyone know anything about a "Vogon Constructor Fleet and some Hyperspace Bypass? Seems we have fifteen minutes to vacate... But I may have misheard what I think I thought I might have heard...)
Anyway, frustrated for the night, I have also discovered this thing can squeal LOUD! Apparently that little 10000x multiplication of the resistance was just enough to quiet it. My faux resistor seems to be doing an adequate job- until a proper resistor makes an appearance. Now to just get all the adjusty thingys adjusted, and I might have a half decent receiver here!
Wouldn't that be nice! My 37-650 a going concern once again. Well, I can dream, can't I?
Still looking for answers/replies/suggestions regarding my earlier questions in this string...
Thanks!
Scott
Old Cars, Old Radios, Old Pipes and Young Women... What more is there?
Posts: 1,703
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City: Evanston, IL
Changing that 330K resistor is good obviously.
One note: The electrolytic cap part 59 n the schematic is DRAWN WRONG.
The POSITIVE end should be grounded and the NEGATIVE side to the HV centertap line.
This is the negative bias filter cap. Be sure you installed your new one correctly. If you followed the schematic, it's in backwards. This will definately upset the grid bias on the 1st. audio and the audio output tubes.
Bwsure that metal-clad power resistor, part 58, is good or replaced. They can open or short to the chassis. This style of resistor is called a "Candohm." It's mounted in the corner of the chassis next to power transformer and the line filter bakelite block.
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City: Minneapolis/St. Paul MN
Scott,
I think you've hit on something major here. Replacing that resistor with the correct value should make a big difference. I'm glad you caught that.
I can vouch for the point Chuck brought up on the incorrect wiring of capacitor part 59 - I ran the radio on and off for 2 days, and after having it on for about 45 minutes on the second day...BANG! The cap blew on me. Measuring the voltage across the connection points verified the cap was wired incorrectly. Put another one in wired the right way (contrary to the schematic), and haven't had a problem since.
At this point, I'd recommend double checking the correct values on ALL the resistors - there may be another one lurking in there. Sounds like you're on the right track. Good luck!
Bill
Sent from my Pentium II on the AT&T Dial Network
Posts: 147
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Joined: Nov 2005
I did recheck the remaining stock of resistors- I have at least 1 of each in the packets they came in, nicely stocked, and all but the one values seem correct. I found a nice convertor http://www.w0mnx.com/resistor_calculator.htm to check the band markings. I will recheck the 59 cap, I followed exctly the directions Chuck gave me as to how it connected to the 59A cap, so I should be ok there. I think it may just be an adjustment issue, but I am keeping an eye out for other causes.
Thanks!
Scott
Old Cars, Old Radios, Old Pipes and Young Women... What more is there?
Posts: 147
Threads: 28
Joined: Nov 2005
Chuck- Thanks for the mention of 59- You discovered it when I was rebuilding the electrolytics, so I took care of that according to your directions... 
How do I check the number 58? Just disconnect it and check for a short? Or do I ohm it out in a particular way? And, if it is a problem, what is usually used to relpace it? I have a spare- a 33-3280-1 removed from a 38-3 chassis I parted out, and could use if it checks out ok...
I only have about 12" of snow outside to deal with, so I might have a little radio playing time for the next couple days...
Scott
Old Cars, Old Radios, Old Pipes and Young Women... What more is there?
Posts: 1,703
Threads: 55
Joined: Sep 2005
City: Evanston, IL
With a Candohm, you should completely disconnect the wiring from it and measure the sections and also for shorts to the metal "wrapper." Anything looks funny, you can sub in a standard terminal lug strip and two resistors.
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Cool- Thanks!
Scott
Old Cars, Old Radios, Old Pipes and Young Women... What more is there?
Posts: 147
Threads: 28
Joined: Nov 2005
The candohm resistor calls for 100 ohms on one side, and 19 on the other. It ohms out at 110 and 21, and there is no indication of a short to the chassis, so I think it should be fine.
I have discovered the 10k ohm, 2 watt metal oxide resistor I used to replace the wire wrapped one number 60 has actually slightly discolored(slightly dirty looking) and the orange band has turned black. It ohms out almost exactly the same as a new one I have sitting here. The original ohms out at about 23k ohms! And the other wire wrapped, number 61 should be 9k ohms, and ohms out at 13k ohms.(This one was replaced with a 4.3k and a 4.7 for the proper total) I have a spare wire wrapped- a 7500 ohm, that ohms out at 10.85k ohms- would it be all right to throw this one in as a test subject? I am not sure of the wattage, it is larger that the 10k ohm.(It came from a 38-3) I'm wondering it I am overloading the metal oxide ones, as they are signifigantly smaller than the wire wrapped, although they carry the same wattage and ohm.
Scott
Old Cars, Old Radios, Old Pipes and Young Women... What more is there?
Posts: 147
Threads: 28
Joined: Nov 2005
Ok, Still having fun here. I am trying to figure out the noise the radio is making: in certain ranges, it sounds like the thing is giving me a raspberry! It sounds like the noise you get when you keep your lips closed, and say "burr" pushing the sound past your closed lips, and holding the note. It varies from soft, to very loud. Is this "motorboating"?
I know there is a condensor which might cause "motorboating", but which one is it?
Thanks again for any help! Scott
Old Cars, Old Radios, Old Pipes and Young Women... What more is there?
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