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#1
11-14-2011, 03:27 AM
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GE L-660 tubes don't work.
 When I got the radio, I can easliy see that someone else has been working on it, but since that type of radio does not have a power transformer, I was not to worried about going ahead to recap.I slowly powered it up on my variac, the dial light is on, but the tubes did not light up. I checked all the tubes on my Heathkit TC-1 tube tester and they are all good, at least they all glow. So my queston is that if all the tube glows on my tester, then if everything was OK in the radio, it should also light up. I am a bit worried that a coil is open,the queston is that if a coil is open, should the tubes still light up? 
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#3
11-14-2011, 11:14 AM
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Hello,
No coil in this radio is related to the operation of the tube heaters. Here is simple test you should try with the radio not connected to the power line. 1 - With the radio off, connect your ohmmeter to the prongs of the power cord. You should get an infinite reading. 2 - Turn the power switch on. You should get some low reading (maybe a few tens of ohms). You are now measuring the cold resistance of the tube heaters in series. If you don't get a correct reading, something is wrong either with one or more tube, or with the wiring to the tube heaters. 3 - Assuming you got a correct result in the previous step, pull any of the tubes. You should get an infinite reading again. By the way, tubes take a few seconds to light up, as you can verify when testing them on your tube tester. Good luck! P.S.: the pilot light is a 110 V unit directly connected to the line, so it may light up even with something wrong with the tube heater circuit. Last edited by electroking; 11-14-2011 at 11:15 AM. Reason: added note
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#5
11-14-2011, 12:15 PM
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I agree with maxhifi. The lamp lights because it's connected directly to the power line, unlike most radios of that ilk, where it's on a heater tap of the rectifier tube.
If it has the tubes I think it has, the 12SA7 goes at the end next to the tuning capacitor. The next one, on the other side of the IF can, should be the 12SK7. After that comes the 12SQ7 and then the 50L6GT, with the 35Z5GT close to the panel.
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| Audiokarma |
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#6
11-14-2011, 12:41 PM
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if you look close, it has an rf preamp before the converter, the converter is hiding behind an if can
So it's sk, sa, sk, sq, then 50L6 and 35z5 But look for a tube location chart on the cabinet, or use the one on nostalgia air Quote:
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#7
11-14-2011, 01:10 PM
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Yes, some tubes are definitely in the wrong places. See figure 1 in the following:
http://www.nostalgiaair.org/PagesByM...0/M0008190.pdf
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#8
11-14-2011, 02:16 PM
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I just love these tube radios!
How was the 6 tube set better than the 5 tuber?
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#10
11-14-2011, 03:24 PM
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I think the answer is not that much related to sensitivity. Your typical 5-tube radio
has enough gain to amplify the atmospheric noise to an uncomfortable level. The advantage of a tuned RF stage is improved rejection of the image frequency, which is useful when the band is open, or when you have a local station at or near the image frequency of the weak station you are listening to. The image frequency is 910 kHz above the actual setting of the dial. For instance, if you set your radio for 660 kHz, you may be able to hear a station transmitting on 1570 kHz. The RF stages will amplify much more at 660 than at 1570 under such conditions, thus improving the performance.
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| Audiokarma |
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#11
11-14-2011, 05:09 PM
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Tubes are in the wrong laces
Quote:
Yes, all the tubes are all in the wrong places and I would have never thought that the diagram was wrong. So now I can't trust the the schematics. I changed all the tubes around , according to the label underneath the cabinet and slowly turned the power back up with the variac and all the tubes light up. Now I have a lot of hum, and if I just touch or tap the rectifier tube 35Z5 it almost sounds like I am taping a microphone. If I just tap it, the hum is louder and then just press on the tube, the hum gets a bit softer again. The whole radio is recapped except two of the molded caps and I have not check the wiring to the schematic to see if it is all that it should be. I recapped the radio exactly to each capacitor what was in the radio, one by one, so I did not make a mistake unless it was wrong before. I am getting zero radio reception and I may just try some other tubes from my stash.
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#12
11-14-2011, 05:27 PM
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Hum means plate voltage is present, and the output tube (35L6GT) is working.
You're on the right path, keep up the work!
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#13
11-14-2011, 09:53 PM
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Quote:
If gain were the only measure of sensitivity, it would be quite useless, as you stated above.
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#14
11-14-2011, 10:18 PM
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Quote:
I think checking the radio against the schematic will probably find the problem faster than typing on here. Measure all the voltages too, and compare vs riders. Double check elecrolytic capacitors for polarity. When you check the wiring, don't take for granted anything in that radio is correct - the speaker is already at least 15 years newer than the radio itself, so who knows what else was changed. If it's not a tube, or something simple, Use signal tracing to fix the radio. Go through the radio stage by stage, and touch the grid of each tube with a screwdriver. Work backwards, starting with the 50L6. You should hear a noise in the speaker each time you touch the grid. When you hear nothing, you have isolated the stage where the signal is dissapearing. Last edited by maxhifi; 11-14-2011 at 10:24 PM.
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#15
11-14-2011, 10:32 PM
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Quote:
You could still have the tubes in wrong and have them lighting up.
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| Audiokarma |
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