[solved] Crosley Model 10-135

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[solved] Crosley Model 10-135

Post by addase on Tue Mar 12, 2013 5:35 pm

Hi, I have a Crosley model 10-135 and I am having issues with the voltages on the heater string. Issue is at the Audio output tube 50C5 where pin 4 the voltage is correct at around 80v but drops to 7.7v at pin 3 instead of 36v. This is then connected to 12BA6 tube where the heater pins 4 and 3 go from 7.7v to 0v and then the rest of the heater string values for the other remaining tubes shows a reading of 0v.
I checked continuity of the wiring between the heater pins of all sockets and they are great. All tubes test good. Not sure what else it could be as to why 50C5 tube uses up 70v at the heater pins when it should be using only 50v. This in turn results in both the 12BE6(converter) and the 12AV6(Det & 1st Audio amp) tube to have no voltage on the heater pins. I am stumped.

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Re: [solved] Crosley Model 10-135

Post by Wildcat445 on Tue Mar 12, 2013 6:00 pm

Do the tubes light? Does the radio work? What problem are you experiencing that caused you to measure filament voltage? I have been working on radios for the better part of 40 years, and have yet to measure string heater filament voltage, for any reason, other than to make sure there was some. I have yet to run across an AA5 with a problem in the heater string, with the exception of open tubes and PCB wiring. Are you using a digital meter? Digital meters only cause me to chase my tail when working on tube electronics. The display bounces around too much for my liking. What is the input (line) voltage? The specs on the schematic is usually for 117 volts. Higher line voltage, common in some areas nowadays, may cause higher readings.

You have checked the wiring and the tubes. That is about all there is on a heater string filament line unless there is a ballast tube or a resistor in the heater string. This is your basic AA5, so there should be nothing like that here.

I have never measured individual tube filament voltages on an AA5 in my life, so I can't comment on that. Are the tubes all in the proper sockets? It would seem to me that if a tube is good, then the filament voltage across the tube should measure close to zero volts. If there were an open heater in a tube in the series string, would not full line voltage appear across the open heater?

What reason did you have for working on the radio to start? Routine restoration work, or was there a specific concern?

I am sure that someone else will chime in with a better answer for you.

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WC

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Re: [solved] Crosley Model 10-135

Post by Wildcat445 on Tue Mar 12, 2013 6:06 pm

OOPS! "Specs" is plural. "Is" is singular. The sentence should read "The spec on the schematic is usually for 117 volts." Sorry. Old age, not illiteracy. I hate poor spelling and grammar. And, I am getting worse, not better!

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Re: [solved] Crosley Model 10-135

Post by Dr. Radio on Tue Mar 12, 2013 8:41 pm

Hi addase, Welcome to the forum.

I'm not sure how you are taking your voltage measurement....

You need to take each probe of your voltmeter and put one probe on pin 3 and the other probe on pin 4 of EACH tube socket.

You will read the full voltage (120 volts or what ever comes in off the power line) across 3 and 4 if the tube filament is open (or has a bad connection to the tube pins)...Otherwise, in a normal radio you will read the approx. voltage necessary, i.e. 50C5 will have about 50 volts AC across 3 and 4.

Also, use caution, since this is an AC/DC set, you should really be using an isolation transformer for protection.
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Re: [solved] Crosley Model 10-135

Post by addase on Tue Mar 12, 2013 10:23 pm

Hi, I should mention why I was looking at voltage across heater pins. I recapped the radio and when I turned it on I got nothing other than a faint hum from the speaker and increasing the volume had no affect on volume of the hum. I noticed that the converter tube(12BE6) and the Det & 1st Audio amp tube(12AV6) was not glowing. I then checked voltages from each socket lug to B-(Pin 7 of 12BA6) and noticed that the heater pin values were very off or showing zero on others. So two tubes are not getting any heater voltage. Here are the AC readings across pins 3 and 4 : 35W4 shows 45v, 50C5 shows 64v, 12BA6 shows 7v and the remaining two mentioned above read 0v. So I am stuck on why and what is causing the heater pins getting too high or no voltage at all. I checked the wiring allong the heater string and they all have continuity. I have recapped many radios in the past but never had come across this issue.

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Re: [solved] Crosley Model 10-135

Post by Wildcat445 on Tue Mar 12, 2013 10:43 pm

If the heater circuit were your only problem, you would hear nothing out of the speaker. No hum, nothing. You possibly have a problem with the high voltage DC (B+), which is not allowing the amplifiers to work. It is not possible that two tubes would not be working, because with two dead tubes, the radio would be totally dead. I personally feel that you are chasing your tail worrying about filament voltage. You need to be more concerned about B+, IMHO. In a series heater string, if one tube is lighting, they all are.

A quick diagnostic test would be to place your finger, or the tip of your plugged-in soldering iron on the center terminal of the volume control. If you hear a loud growl, the audio section, from the volume control thru the speaker is working okay. The problem would then be from the volume control back to the antenna. If, on the other hand, there is no or weak output from the speaker, you have a problem in the audio section, from the volume control to the speaker. This quick test will give you some indication at least where to start looking for the trouble. Working with the schematic, and measuring all element voltages, you should quickly be able to diagnose and repair the trouble.


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Re: [solved] Crosley Model 10-135

Post by addase on Tue Mar 12, 2013 11:54 pm

Hi WC,
Having touched the center terminal of the vol with my plugged-in soldering iron I got very little buzz. But when I touched the grids pin 2 and 5 of the 50C5 I got a very loud disturbance. Measuring the DC voltages from B-(pin 7 of 12BA6) I got a high reading of 85v on the plate of 12AV6(Det Audio Amp) tube instead of 50v as per the schematic and I got 0v on pin 1 grid of the converter tube instead of -9.5 as per the schematic. All other plate voltages of the other tubes were around what they should be. Any Idea what the problem might be based on these readings?

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Re: [solved] Crosley Model 10-135

Post by addase on Wed Mar 13, 2013 12:09 am

I also got a load buzz disturbance when I touch the plate of 12AV6(pin 7)

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Re: [solved] Crosley Model 10-135

Post by Bill Cahill on Wed Mar 13, 2013 12:17 am

Don't touch that! You want to get electrocuted?
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Re: [solved] Crosley Model 10-135

Post by addase on Wed Mar 13, 2013 12:20 am

I was only touching it with my positive lead of my volt meter when taking measurements and noticed disturbance on the plate of the 12AV6.

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Re: [solved] Crosley Model 10-135

Post by Wildcat445 on Wed Mar 13, 2013 12:55 am

Let us start with the speaker and audio output tube, the 50C5. What kind of voltage do you have on the plate of that tube? This voltage is fed to the plate of the tube thru the primary of the audio output transformer. Close to the correct voltage will eliminate the audio output transformer as a suspect. Then go to the grid of the 50C5. It should not have a positive voltage. You say you get a "loud disturbance" on the plate of the 12AV6. Is that a click or a loud growl? A click would be a normal reaction of having made contact with the plate. No growl or buzz touching the center terminal of the volume control places suspicion on the audio output stage. You will want to start at the speaker, and work back to the volume control. Subbing another speaker, known good, would not hurt anything just for grins. It is unlikely to be the problem here, however. You need to check absolutely every connection with the schematic and check your work for unintended faults. Don't feel bad if you find one. We all do it, so just fix it and figure you have learned something. There is an orderly flow of electricity thru your radio. There is nothing mysterious about it. When we find what is interrupting either the signal or the voltage required to carry it, the trouble will be revealed.

The grid of the 12AV6 should be more negative than it is. The plate voltage is high. This would indicate to me that this tube is not conducting current, thereby drawing down B+ to a more normal reading. Measuring the grid voltage on the 50C5 may yield a clue as well. Positive voltage here may indicate a leaky coupling cap between the plate of the 12AV6 and the grid of the 50C5. Insufficient negative voltage on the grid of the converter tube may indicate that the oscillator is not running. I feel you are getting ahead of yourself. Please, just measure the voltages in the audio section as we have suggested above, and let us take this a step at a time. A shotgun approach will not be successful. An orderly diagnostic approach will yield more successful results, and we may all learn something.

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Re: [solved] Crosley Model 10-135

Post by Wildcat445 on Wed Mar 13, 2013 12:59 am

Disregard my comments about the grid of the 12AV6. I misread the post. Sorry.

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Re: [solved] Crosley Model 10-135

Post by addase on Wed Mar 13, 2013 2:13 am

Voltage measurements on the 50C5 are: pin 7 plate 93v good, pin 6(GS) 90v good, pin2 & 5 (G) are both slight positive but not 0 as per schematic, pin 1 (K) is 6v good.

For the 12Av6: pin 7 plate is 85v instead of 50v very high, pin 1 (G) is slightly neg and other pins are showing proper readings.

I recapped the radio including the coupling cap between 12AV6 and grid of 50C5 so I don't think I have a leaky cap.
I will go through and check all of my solder connections I did when recapping.
Also when I touch the plate of the 12AV6 I get a loud growl or some call it a loud buzz the same sound I get when touching the grids of the audio output tube.

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Re: [solved] Crosley Model 10-135

Post by Resistance is Futile on Wed Mar 13, 2013 2:26 am

Make sure your tubes are in the right order, you never answered a question of do all tubes light?

Take your meter and put on the incoming hot AC. Use the other lead to test the filament chain. When you find no voltage then that is the area to inspect, that includes cold solder joints, a wire that looks connected but could be broken inside the insulation or a wire that has fractured through but is so fine you can't see the crack.
you could also remove all tubes and check filament socket to filament socket wires to find an open.

Also check the last filament wire to chassis ground for continuity, then chassis ground to the return AC wire.
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Re: [solved] Crosley Model 10-135

Post by addase on Wed Mar 13, 2013 2:37 am

I did test all of the wires in the heater string and all show continuity even through the sockets with the tubes out. But when I measured the resistance of the entire heater string with tubes in I got 85 ohms instead of 115-120 ohms that I should be getting. Not sure if this has anything to do with the problems I am having with this radio.

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Re: [solved] Crosley Model 10-135

Post by Bill Cahill on Wed Mar 13, 2013 3:02 am

Sounds like a short to me.
What kind of wiring do you have? Is it rubber? Is the insulation falling off, and, cracked?
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Re: [solved] Crosley Model 10-135

Post by Resistance is Futile on Wed Mar 13, 2013 5:18 am

addase wrote:I did test all of the wires in the heater string and all show continuity even through the sockets with the tubes out. But when I measured the resistance of the entire heater string with tubes in I got 85 ohms instead of 115-120 ohms that I should be getting. Not sure if this has anything to do with the problems I am having with this radio.
One step at a time as has been mentioned.
1. Test tubes
2. Make a chart as shown from the schematic for pin voltages.
then write your readings next to the listed voltages.
3. concentrate on area(s) of low readings.
4 . measure resistances and check caps, then coils in suspected areas.
to me Sounds like a shorted filament! If you are getting B+, if B+ is too high then a resistor is out of range or cap is open. If voltage is too low then a component is loading circuit by shorting out or resistance is too low. Grid voltages are controling plate voltages and if they are wrong then plates will be wrong too. So grid circuitry are / is suspect.
-------------------------------------------------
1. BOTTOM VIEW OF SOCKETS
2. voltages measured with electronic voltmeter from socket lug to B- (Pin 7 of 12BA6)
3. Measured with the volume at minimum and no signal into loop, tunning gang closed.
Socket voltage tolerance + or - 10%



12BE6 CONVERTER
PIN 1 -9.5
PIN 2 0
PIN 3 12 VAC
PIN 4 24 VAC
PIN 5 88
PIN 6 88
PIN 7 -1

35W4 RECTIFIER
PIN 1 WIRE JUNCTION
PIN 2 WIRE JUNCTION
PIN 3 84 VAC
PIN 4 117 VAC
PIN 5 117 VAC
PIN 6 NO CONNECTION
PIN 7 119

50C5 AUDIO OUTPUT
PIN 1 -5.1
PIN 2 0
PIN 3 36 VAC
PIN 4 84 VAC
PIN 5 0
PIN 6 86
PIN 7 98

12BA6 I-F AMPLIFIER
PIN 1 -1
PIN 2 0
PIN 3 24 VAC
PIN 4 36 VAC
PIN 5 88
PIN 6 88
PIN 7 0 (B-)

12AV6 DET-AVC & 1ST AUDIO AMPLIFIER
PIN 1 -0.8
PIN 2 0
PIN 3 0 VAC
PIN 4 12 VAC
PIN 5 -0.8
PIN 6 0
PIN 7 50
Power supply is always the first to be checked as it is the backbone of other voltage checks.
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Re: [solved] Crosley Model 10-135

Post by Wildcat445 on Wed Mar 13, 2013 12:35 pm

This same thread is on ARF. The OP actually quoted one of my posts. How many times do we have to give him the same information? I guess if he asks the question often enough he will get the answer he wants.

This whole matter could be simplified considerably by answering one question. DO THE TUBES LIGHT? Geesh.

Edit....After reading this thread again, top to bottom, perhaps both Cliff and I have missed something. Apparently the tubes light, witnessed by the fact that B+ on the output tube is okay. If I read right, there is a growl obtained from the speaker when touching the plate of the 12AV6, indicating the audio stage is working, at least from the plate of the 12AV6 thru the speaker. Fine. Again, if I read correctly, there was no growl at the center terminal of the volume control. The voltages on the 12AV6 were kinda close (?)

I dug out an AA5, removed the chassis and tinkered with measuring the resistance of the heater string, something I have never done in my life. The resistance I measured was not dead on specs, either. There is one conceivable condition that would cause a tube to not light, but the audio section would work. That is if something, like a solder blob or a miswire actually bridged the filament of a tube, allowing the other tubes to work, but the tube with the bridged filament to be dead. A three second inspection should reveal such a fault. And, would not the voltages on the other tube filaments be higher than normal, since they have to share the dropped voltage of the bridged filament?

IMO, worrying about a few ohms difference in resistance from spec is not the issue here. There is something else going on. Maybe a dead converter. Could be anything. I will be happy to help any way I can, and I wish the OP well in his endeavor.

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Re: [solved] Crosley Model 10-135

Post by Resistance is Futile on Wed Mar 13, 2013 1:57 pm

I think we addressed a similar thread here, a short while back too. If we had kept the new section on top I would have been able search this topic fast. But there was a slow down issue on some peoples computer. Sigh.
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Re: [solved] Crosley Model 10-135

Post by Wildcat445 on Wed Mar 13, 2013 2:14 pm

The OP insisting on measuring and re-measuring the filament resistance, and not concentrating on systematic diagnostic procedures is kinda like having the toilet stopped up and worrying about whether the porch light is working.

I have probably done all I can do for the OP, at least until he adopts more reasonable diagnostic procedures and abandons his shotgun methods.

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Re: [solved] Crosley Model 10-135

Post by addase on Wed Mar 13, 2013 4:04 pm

thanks for all the suggestions, here is where I am at today with this radio: all tubes are checked good.

Checked voltages both AC and DC and here is what I am getting: 35W4 Pin 4 120ac and pin 3 77ac a consumption of 47ac; 50C5 pin 4-77ac pin 3-7.7ac a draw of 70v and then 12BA6 pin 4-7.7v pin 3-0v and then the remaining 2 tubes show 0v at both pin 4 and pin3. As far as the DC plate voltages all tubes except 12AV6 show close to proper values but 12AV6 plate value is 85v instead of 50v as per voltage chart. All wires connecting heater string are good with no breaks. I did test the ohm readings as suggested starting at pin 3 of 12AV6 to pin 4 of the other tubes and got at 12BE6 5ohms, 12BA6 6 ohms, 50C5 60 ohms and 35W4 91 ohms so no break in connection.

Also I did an interference or Buzz test on the grids of 50C5 and got load buzz on both pins 2 and 5 but on the 12AV6 i got no interference or buzz on pin 1 BUT I did get a loud buzz when touching the plate pin 7.
So I assume that the audio output stage is ok but somewhere from the detector stage and back is probably where the problem arises. I did recap all 8 paper caps and the electrolitic caps so C14 should be good. Not sure what to look at next, only thing that stands out right now is that the heater pins of 12AV6, 12BE6 and 12BA6 are not getting the voltages shown on the voltage chart.

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Re: [solved] Crosley Model 10-135

Post by Wildcat445 on Wed Mar 13, 2013 4:22 pm

The audio section is probably working okay for now. The problem is not in the filament circuit. The tubes are lighting.

The problem now has been determined to be somewhere AHEAD of the volume control. From the antenna to the volume control. You need to get the radio "talking" at this point. You can always tune it up to work perfectly after this is accomplished.

What kind of test equipment do you have? A signal generator? A signal tracer? If not, you may have a tough time with finding the fault in your radio. I would inject a signal, at the IF frequency, one stage at a time, until you find where the signal is being lost. I would start at the plate of the IF tube, 12BA6, then the grid of that tube, then the plate of the 12BE6, then the grid, then the antenna. Somewhere, the signal will not pass. That point is where you concentrate your efforts. You can test the oscillator coil to make sure it is not open. The schematic will give the value of acceptable readings. Check for negative voltage on the gird of the converter tube, 12BE6. If there is none, the oscillator is not working. You can tune another radio to 1455 kc and the radio under test to 1000kc and see if you hear the oscillator squeal in the other radio. Make sure the wiring and all the connections are good in the "front end" of your radio. Sub the 12BE6 with another tube KNOWN GOOD. Oscillator tubes can be a finicky lot sometimes. They will fail to work in one radio, but will work just fine in another. The IF transformers can be badly out of alignment. To check the front end of a radio, certain test equipment is necessary to adequately and successfully diagnose problems. It would not hurt to sub the 12BA6 just for grins. A tube can test good, but fail to work in the circuit.

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Re: [solved] Crosley Model 10-135

Post by addase on Wed Mar 13, 2013 4:34 pm

thanks for the help I will follow up, but I do want to mention that with the radio on I only see the 50C5 , 35W4 and the 12BA6 lit and the other two are not. I even pulled out one at a time the 12BE6 and then the 12AV6 and the other 3 tubes remained glowing so I am sure that the two tubes just mentioned are not getting any AC power and the other 3 are using up all 120v and I assume that is why both 50C5 and 35W4 are very hot to touch or maybe that is normal to be that hot, anyways the two tubes are not getting AC. I will try and replacing those tubes but I don't think it will make a difference.

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Re: [solved] Crosley Model 10-135

Post by addase on Wed Mar 13, 2013 7:34 pm

Well I don't really know what I did or what just happened but I took another radio as suggested and tuned it to 1455c and then turned on the Crosley and I started to pick up stations very clear and I was checking the pin 1 of the converter tube to see if I was getting neg voltage and at first it stopped receiving stations. I turned it off then back on and it didn't receive at first but once I turned on the other radio again it started playing. I poked around the socket of the 12BE6 and it seemed to have caused the tube to come alive. I turned off the Crosley waited and turned it back on and it is playing without the aid of the other radio on. I am not sure if that other radio had anything to do with it or if I moved something on the 12BE6 socket to make contact but it may have been an oscillator issue all along. I am confused at what just happened but I am listenning to the radio very clear and crisp reception.

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Re: [solved] Crosley Model 10-135

Post by Wildcat445 on Wed Mar 13, 2013 9:04 pm

You just proved that there was nothing wrong with the filament circuit. The radio is working, so obviously the tubes are lit. You did what was suggested in the earlier posts on this thread. You found a connection that was bad. The 12BE6 converter tube was not making good connection in its socket. It is rather difficult for those of us trying to help when the radio in question is not in front of us. Congrats on your radio working again. The other radio probably had nothing to do with your radio working again. It might be a good suggestion to take needle nose pliers and squeeze the terminals on the tube sockets GENTLY together in order to make good contact. The best part is that you learned something and did not give up. Finding and reading a good text on radio repair and diagnostics would not hurt a thing.

The 35W4 (rectifier) and the 50C5 (audio output) tubes run hot since they handle power. This is normal. It can be difficult to see the filaments lit in some tubes. A good dose of DeOxit on the tube sockets may help eliminate bad connections. There is no way to remove a tube from a series heater string and allow some tubes to remain lit. Since the heaters are in series, removing a tube will make all the tube filaments go out.

Regards

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