GE L-660 tubes don't work.

[Electronic M]

Antiquated wireing errors do happen. I bought and sold a late 40's Crosley it had hum and all-original caps, except for the filter cap which was a 50's-60's replacement. Well the origional was wired in wrong I replaced it the same way they did, and it still hummed. I didn't have a schematic for it, and coulden't figure it out so I sold it. The next owner informed me what was wrong.

[HiFiCanada]

Originally Posted by maxhifi

Double check that all the tubes are in the right places. The 35Z5 can cause hum related problems sometimes, try replacing it.

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.

Thanks ,I'll try that this weekend I have got some time to go through everything and try to isolate the problem.

[HiFiCanada]

Just have a queston, are the electrolic capacitors supose to be pointing that way? The schematic does not tell me were to + should be wired to. With my limited experence, I think it's wrong. If the volume is turned up it does not affect the hum that much.
I touched the grid of each tube and the only tube that makes a sound out of the speaker is the audio the 12SQ7. I did switch all the tubes , and that did not change anything. The 1000 ohm 2 watt resistor`gets hot fast and it is to hot to touch.
The 40 Uf is wired from the power swith to tube socket 12SA7 pin S and the 30uF is wired from switch to the rectifier tube, pin K.

[Electronic M]

Electrolytics tend to smoke and go BANG! when connected backwards or accross AC (trust me, I used to take ones from scrapped SS audio equip and get the cans to shoot a good 10-50' ). If the lytics are connected to the right terminals and don't heat up then you should have the polarity right.

[maxhifi]

i didn't know all the resistors were also changed when the capacitors were done.
You really need to compare this with a schematic diagram - now that you know the audio stage is good go back from there

[HiFiCanada]

I had a gut feeling, right for the start that I'll never get this one working. I'ii spend a few weeks on it, after that it gets bolted back into the cabinet. I'll trace every circuit secton at a time, see what I will find and test the molded caps, it just sounds like one is shorted.
I'll post back with a big Yahoo when I do get it up and running.

[maxhifi]

Have you got an rf signal generator or an oscilliscope? Keep trying and you'll win, these hard repairs are the ones i like best, because i learn something. To me the troubleshooting process is more fun than the reward of hearing right wing talk radio come in clearly anyway!
Also, just out of curiosity, where in Canada are you? I live in Edmonton - it is an excellent weekend to be inside with a warm tube radio here!

[electroking]

This radio has preset capacitors, as eall as a main tuning capacitor on the chassis.
If there is anything wrong with this assembly, the radio won't work. Check the
schematic, and then make sure the main tuning capacitor has continuity
to the rest of the circuit. You should then be able to verify local oscillator
operation as follows:

Get a working radio (a small transistor portable will be fine) and set it to about
1100 kHz. Set it on the table close to your tube radio. Set the tuning knob
of the tube radio around 645 kHz, and move it back and forth a bit. You should
hear some noise in the small radio, indicating that the LO of your tube radio
is working at 455 kHz above the dial frequency as it should.

You may then increase the setting on both radios and see that the LO is tracking.
There are many more parts in a radio than the local oscillator, but that has
to be operating properly in order for the radio to operate.

I you have two working AM radios, you may also try that with them just to
find out how it should sound. Good luck!

[HiFiCanada]

Originally Posted by electroking

This radio has preset capacitors, as eall as a main tuning capacitor on the chassis.
If there is anything wrong with this assembly, the radio won't work. Check the
schematic, and then make sure the main tuning capacitor has continuity
to the rest of the circuit. You should then be able to verify local oscillator
operation as follows:

Get a working radio (a small transistor portable will be fine) and set it to about
1100 kHz. Set it on the table close to your tube radio. Set the tuning knob
of the tube radio around 645 kHz, and move it back and forth a bit. You should
hear some noise in the small radio, indicating that the LO of your tube radio
is working at 455 kHz above the dial frequency as it should.

You may then increase the setting on both radios and see that the LO is tracking.
There are many more parts in a radio than the local oscillator, but that has
to be operating properly in order for the radio to operate.

I you have two working AM radios, you may also try that with them just to
find out how it should sound. Good luck!

Thanks, I'll try that.
I have progressed backwards, only half the tubes light up now. I found that the electrolic capacitor was backwards according to the schematic, indicates black and red and black and yellow for the paper cap can that was in there, someone had replaced it.
Black is neg side and red is postive side and also black is neg and yellow is positive side of the electrolic capacitor on the schematic. It does not have the + sign like some of the newer schematics have.
I ran out of time , but I when I unsoldered the cap, I must have had a wire come off at the same time.

[electroking]

Just a bit of advice: if your electrolytic was connected backwards to a working
rectifier, it should be replaced with a new one.

Regarding the tubes lighting up, get back to the test I described earlier:
you should have continuity with all the tubes in, and an open circuit when
you pull any tube. You can do this test even if the electrolytic capacitor
is not connected. Good luck!

[holmesuser01]

Also regarding the tubes lighting: If the B+ voltage is gone, your metal tubes won't get nearly as warm with just the filaments lit as they do when they are powered and conducting.

--Learned this one the hard way...

[HiFiCanada]

Originally Posted by electroking

Just a bit of advice: if your electrolytic was connected backwards to a working
rectifier, it should be replaced with a new one.

Regarding the tubes lighting up, get back to the test I described earlier:
you should have continuity with all the tubes in, and an open circuit when
you pull any tube. You can do this test even if the electrolytic capacitor
is not connected. Good luck!

Will do, I have a few instock.
Thanks for the info and great learning tips, I would not have know to replace the electrolic cap again. This radio is sure a good learning tool, almost pricless.
I remember my Heathkit days back in 1966, I best really check this radio out to the schematic, bit by bit before I power up again. I got another radio that works and I plan on checking all the tubes. I also want to check all the coils just to make sure that is good.

[HiFiCanada]

I replaced the electrolic capacitor and put in all good working tubes that worked in the other old radio, and now they all work.
When I touch the phono wire there is a good strong AC hum. The Radio can pick up plenty of radio stations if I squeeze the coil just a bit on both AM and Short wave, but if I don't touch the coil, I get absolutely nothing. Turning the tuning knob , checking for stations on the dial does not work yet.
But I am getting closer to finding the problem now, 12SK7 R.F. ,12SA7 and 12SK7 I.F. amp tubes are not warm enought and are easy to touch after runing the radio for 15 minutes. I got to have a power loss some were by 12SK7 and the Audio tube which gets good and hot, maybe to much and I best do the voltage checks on the hot ones first, just to be sure that they art not getting to much voltage. Then if that is ok, then I will trace were I am losing voltage. Looking at the schematic, that should not be possible.
S0-oooooooooooooo I am stuck.

[maxhifi]

I'm thinking it could be contacts for those push button tuning switches. Have they been cleaned and verified good? Check osc. coil for continuity too, and antenna.

[HiFiCanada]

Originally Posted by maxhifi

I'm thinking it could be contacts for those push button tuning switches. Have they been cleaned and verified good? Check osc. coil for continuity too, and antenna.

I checked and cleaned the push buttons , I tightened the tube socket pins and Deoxit , not it does not crackle when I move it around, not as intermittent.
I used my alarm clock radio and set it beside the radio,and turned the tuning dial which was aprox at 455 it does produce static on 1000kh .
I brought out my Heathkit RF signal generator SG-8 and set to 455 KC and soldered a .02 uF cap on the end of my home made test cable, the 12SA7 is very active, just 4 inches away, I can hear the signal tone from the generator, and later applied that signal to the grid of the 12SA7 and aligned the trimmers in the 2nd and first stage making that as loud and clear as I could get it. That worked very well and was very clear, so everything from the rectifier and audio to 12SA7 seems to work well, the IF alignment was done according to the procedure for the L-660.
I set the frequency generator to 1500KC, and turned the variable tuning cap all the way open, and with the loop antenna hooked back up again, tried to set C2B and C2A adjustments on the variable cap,but no signal.
I checked the signal generator with my clock radio at that frequency and it does work very well, so the problem lies by the RF amp and antenna and switches.

I don't think that the former owner had the loop antenna wired right, it was connected to RF, 12SK7, pin 3 and 4, I will follow the schematic and check that all out, as connecting the loop antenna does nothing, not even pulling in the strong signal from the frequency generator.