finally beginning 118 - Printable Version
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Re: finally beginning 118 - Glenn Roberts - 01-23-2012
No worries. Glad to help. I'm hoping to build my coil winder this week and get the shadowmeter coil rewound. Then I can start on the dial cord and reassembly.
Glenn
RE: finally beginning 118 - Glenn Roberts - 06-16-2012
Ok Now the shadow meter is behind me and it was successful and I have cleaned the chassis as well as possible, I reassembled the tubes and shields and fired it up....
I had no sound at all from the speaker, The speaker is fine and when I change settings on the tone control I get a small pop. I checked the volume control, it's bad..reading 4-8 meg, should be 350k max. Replaced it, still nothing, so I checked all the voltages...all within limits. Before I stated checking voltages I had no hum either at the grid caps when I touched them.
Here is where it gets a little goofy, I flip the chassis over and touch the top of the 75 tube...it hums. I touch the top of the 6a7 I get reception...for 30 seconds then it stops, but only at the grid cap, nothing through the antenna connection and only while it is connected to the tube. If I remove it it goes silent again. Now my readings on the 6a7 are 100 VDC P-K s/b 180 and 90 VDC S-K s/b 175.
I'm leaning toward a bad solder connection, but before I go back through all the connections (there are many) any suggestions as to where I should start first? It has to be in the rf section,
Here is a link to the schematic:
http://www.nostalgiaair.org/PagesByModel/125/M0013125.pdf
Thanks for your help,
Glenn
RE: finally beginning 118 - Glenn Roberts - 06-17-2012
Progress..I found the loose solder joint and corrected it. I still need to track down the reason I'm not getting anything through the antenna connection, only straight to the top of the 6a7 tube. Checked the antenna coil it seems fine I have low ohm readings where I would suspect them. checked the wavetrap, it's fine. Enough for today, I'll get back to it tomorrow, hopefully. Vacation is over and I didn't get the 118 back together,
. Tomorrow is a another day. Suggestions...I'm open to any at this point. I need an AA5 after this one..
.Glenn
RE: finally beginning 118 - TA Forbes - 06-17-2012
Has to be in the antenna/RF section somewhere.
1. Does transformer 12 have continuity?
2. Is the gridcap on the RF (78) tube secure? I mean the one permanently affixed to the top of the tube.
3. Are R8, C9, and C13 good?
4. Is there an issue with some of the bandswitch contacts?
Does the problem exist on both the Shortwave and the Broadcast bands?
RE: finally beginning 118 - Glenn Roberts - 06-18-2012
Thanks for the info Tom. I'll check these out when I get home. I did recap, but you know sometimes they go bad. The problem is on both bands.
Glenn
RE: finally beginning 118 - Glenn Roberts - 06-18-2012
Success...WooHoo. The number 13 mica was wayyy out of spec, replaced it and in the process found the ground strap to the tuner grounding the input of the bandswitch., ooops 
, moved it away and it plays good and strong after an alignment. Now the shadowmeter isn't moving so time to do some more research. The coil reading is correct, but the voltage is only changing 7 VDC on the strongest station I receive and it barely moves.
RE: finally beginning 118 - Glenn Roberts - 06-20-2012
OK..deep breath...I started this because it was relaxing, well until I started this 118. It is kicking my butt, now it's doing goofy things, i.e. it plays for an hour then nothing except a little static from the speaker. I turn it off then wait an hour, turn it on, my Isolation transformer circuit breaker pops, I pull the rectifier it comes on, I check the rectifier it's good, no shorts. Ohm check the trans, it's fine. power it up and check voltages, good. Check wiring nothing appears to be rubbing or bad. Put the 80 back in fires up and plays...for an hour. I'm about to donate it to Ron to sell Saturday as is because honestly I'm sick of looking at this chassis.
Pardon my rant I needed to get it off my chest, if there are any suggestions please let me know.
Thanks,
Glenn
RE: finally beginning 118 - Ron Ramirez - 06-20-2012
I wish I had another 118 chassis to give you, Glenn, but I don't.
RE: finally beginning 118 - Glenn Roberts - 06-20-2012
No worries Ron, I do I got it as a parts chassis but it might be better. I'm thinking of moving it over section by section, the wiring is in better shape But I'm going to give it a day or two and work on something else in the meantime. My Brother-in-law brought me a Gibson tube amp to go through. Might be a nice change of pace.
Glenn
RE: finally beginning 118 - TA Forbes - 06-21-2012
Good idea, Glenn. When a set kicks your ____ (rhymes with "grass"), it is always a good idea to move to something else.
Isaac Asimov once said that when he was unable to solve a difficult problem, he would leave the problem alone and go see a "B" movie or read a pulp novel, and usually after doing so he would return to the problem with a fresh outlook and solve it.
RE: finally beginning 118 - TA Forbes - 06-21-2012
At this point, I am inclined to believe that the problem with your set playing for an hour and then shutting off has something to do with heat. I would think tubes first and transformers next.
Does the power transformer get VERY hot?
RE: finally beginning 118 - Glenn Roberts - 06-21-2012
Good advice Tom. The power trans does get warm, but not hot. After thinking about it, I'm considering the big power resistor. I'll check it out next week. Thanks for you help Tom.
Glenn
RE: finally beginning 118 - TA Forbes - 06-21-2012
Getting warm is fine. You could have a tube or a transformer that is bad with heat.
1. Have a set of tubes handy and when the set shuts off, replace until it works.
2. When the set shuts off, check transformer continuity. I would initially look at windings that pass B+. Also field coil and filter choke.
RE: finally beginning 118 - Radioroslyn - 06-21-2012
Also after it warms up double check the tubes to see that all are lit.
Terry
RE: finally beginning 118 - Glenn Roberts - 06-21-2012
They are..I put it away..I hate not finishing it but I'll spend time on it next week. Thanks for the advice. I'm sure I'll need more when I start it again.
Thanks
Glenn