Thanks!
Not sure why you would expect to have 2 VAC on pin 2 of these two tubes- pins 2 and 7 are the heater connections for both tube types (octal base). With the set turned on, you should measure 6.3 VAC between these two pins, and either 6.3 VAC or zero V from one pin or the other to ground, depending on which one is grounded to the chassis.
BTW, what make is your radio?
::Hi there, I have a 6d336 chairside, I am getting noise out of the speaker, but no reception. I know some electronics....seems everything is ok but i am not getting 2 Volts AC on pin 2 on tube 6a8g and pin 2 on the 6q7g....I tested these tubes to be fine.
::Im not sure what is preventing the 2V AC from getting to these pins...
::I cant seem to upload the schematic pdf...sorry, I know that doesn't help....
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:Not sure why you would expect to have 2 VAC on pin 2 of these two tubes- pins 2 and 7 are the heater connections for both tube types (octal base). With the set turned on, you should measure 6.3 VAC between these two pins, and either 6.3 VAC or zero V from one pin or the other to ground, depending on which one is grounded to the chassis.
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:BTW, what make is your radio?
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You can email me at lorenz200w@yahoo.com
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OK, I see what's going on now. This is a series-string heater radio. It appears that the voltages given on the diagram are the heater voltages you would expect to get with respect to ground. However, this isn't particularly useful info if the tubes are lighting up. If they don't light up, you have a burned out tube or bad ballast unit. If they do light up, I think that I would start troubleshooting this set by checking B+. It should be > 100VDC at the screen of the audio output tube (25L6). Next, check all the plate voltages- should be 80-90 VDC or so. If you find one that is "dead", chances are you have a burned-out IF transformer primary, or an open resistor feeding that plate. A fault like this will need to be fixed before the set has any hope of working.
If all the plate and screen voltages look reasonable, I'd start looking for bad coupling capacitors. A shorted coupling cap will transmit DC into the next stage's grid, sending that tube into the "full conduction" state, and an open cap will simply prevent the AC signal from being passed through it. At this point you might want to consider replacing all of the paper caps in the set.
::thanks Tom...ya I am confused about the schematic i am reading, it's a zenith..Idon't think I can send you a file through here, do you have an email address I can send you the schematic that is confusing me..ya i assumed 2 and 7 where the heater but the info maybe wrong....thanks i will send you the file at your other address if you dont mind that would be a great help!
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:OK, I see what's going on now. This is a series-string heater radio. It appears that the voltages given on the diagram are the heater voltages you would expect to get with respect to ground. However, this isn't particularly useful info if the tubes are lighting up. If they don't light up, you have a burned out tube or bad ballast unit. If they do light up, I think that I would start troubleshooting this set by checking B+. It should be > 100VDC at the screen of the audio output tube (25L6). Next, check all the plate voltages- should be 80-90 VDC or so. If you find one that is "dead", chances are you have a burned-out IF transformer primary, or an open resistor feeding that plate. A fault like this will need to be fixed before the set has any hope of working.
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:If all the plate and screen voltages look reasonable, I'd start looking for bad coupling capacitors. A shorted coupling cap will transmit DC into the next stage's grid, sending that tube into the "full conduction" state, and an open cap will simply prevent the AC signal from being passed through it. At this point you might want to consider replacing all of the paper caps in the set.
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:Thanks again Tom...I just shut the lights out and all tubes ARE lighting up, but still no reception,,sounds like its trying though, when I touch the antenna the noise gets stronger....
:I checked the screen at voltage like you said and there's 104VDC so thats ok...
:The plate voltages of all tubes are around 100VDC (higher than you said 80-90) a couple 104v...plate of 25z6g is -7VDC, im assuming different because this is the rectifier tube?
:this radio has been eletronically restored, all the capacitors are new.I will start checking resistors...kinda lost!
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:::thanks Tom...ya I am confused about the schematic i am reading, it's a zenith..Idon't think I can send you a file through here, do you have an email address I can send you the schematic that is confusing me..ya i assumed 2 and 7 where the heater but the info maybe wrong....thanks i will send you the file at your other address if you dont mind that would be a great help!
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::OK, I see what's going on now. This is a series-string heater radio. It appears that the voltages given on the diagram are the heater voltages you would expect to get with respect to ground. However, this isn't particularly useful info if the tubes are lighting up. If they don't light up, you have a burned out tube or bad ballast unit. If they do light up, I think that I would start troubleshooting this set by checking B+. It should be > 100VDC at the screen of the audio output tube (25L6). Next, check all the plate voltages- should be 80-90 VDC or so. If you find one that is "dead", chances are you have a burned-out IF transformer primary, or an open resistor feeding that plate. A fault like this will need to be fixed before the set has any hope of working.
::
::If all the plate and screen voltages look reasonable, I'd start looking for bad coupling capacitors. A shorted coupling cap will transmit DC into the next stage's grid, sending that tube into the "full conduction" state, and an open cap will simply prevent the AC signal from being passed through it. At this point you might want to consider replacing all of the paper caps in the set.
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That's pretty low- the tube will work at that voltage, but there's no good reason for it to be that low. The plate is a 220 Kohm resistor away from B+ so something is biasing the 1st audio amp triode (part of the 6Q7 tube) way into its conduction curve. You might try setting the volume control to minimum and remeasuring the plate voltage- if it pops up closer to B+ (>100 VDC), it's probably OK; if not, the 6Q7 grid bias is set too positive, due to an open/wrong resistor, shorted AC signal coupling cap, or miswire. Any set that has extensive work done to it (such as recapping, in your case) is a candidate for having miswires.
However, I would still check the tubes out before I spent much time on chassis troubleshooting. Might as well pick the "low hanging fruit" off the troubleshooting tree first.
::...oh the plate of 6q7g is only 56vdc..
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:That's pretty low- the tube will work at that voltage, but there's no good reason for it to be that low. The plate is a 220 Kohm resistor away from B+ so something is biasing the 1st audio amp triode (part of the 6Q7 tube) way into its conduction curve. You might try setting the volume control to minimum and remeasuring the plate voltage- if it pops up closer to B+ (>100 VDC), it's probably OK; if not, the 6Q7 grid bias is set too positive, due to an open/wrong resistor, shorted AC signal coupling cap, or miswire. Any set that has extensive work done to it (such as recapping, in your case) is a candidate for having miswires.
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:However, I would still check the tubes out before I spent much time on chassis troubleshooting. Might as well pick the "low hanging fruit" off the troubleshooting tree first.
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Those are good plate readings for a transformerless set. The rectifier tube plate has AC only on it. Pulsating DC is on the cathode of the rectifier, which gets smoothed out by the big filter capacitors and the speaker field coil.
Do you know if the set worked after it was recapped, or did the previous owner give up and sell it? If it worked after recapping, I think that I would poke around for bad (or missing!) solder joints on the replaced parts. However, you should try the following tube-related things first:
(1)Check that each tube is in its correct socket. This got me on a SABA Freiburg 6 the other day, and I've been repairing tube sets for 45 years. (In my defense, I didn't have a tube layout for the set and it was different from that of the SABA Freiburg 9 that I was using as a general guide!)
(2) It's possible that you have a tube that just went bad (low emission). Most tubes don't burn out; they deplete the electron-emitting layer from the cathode sleeve and even though they light up, their cathodes can't boil off enough electrons for the tube to conduct current. This may seem like it would be noticeable due to performance degradation over time, but often it is as abrupt as switching off a light bulb- the tubes have very wide operating ranges and will often only fail at a "tipping point" where they cannot operate any more. Recommend that you get your tubes tested, or line up a set of known-good substitutes that you can swap in and out, one at a time.
My guess is a bad connection from a chairside radio being bumped around.
Cold solder joint, faulty volume control or a similar infuriating small detail.
Touching tube grid pins with a screwdriver or the DMM lead can sometimes help trace the problem to a specific area. Good Luck.
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::Those are good plate readings for a transformerless set. The rectifier tube plate has AC only on it. Pulsating DC is on the cathode of the rectifier, which gets smoothed out by the big filter capacitors and the speaker field coil.
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:If it worked after recapping, I think that I would poke around for bad (or missing!) solder joints on the replaced parts. However, you should try the following tube-related things first:
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::(1)Check that each tube is in its correct socket.
::(2) It's possible that you have a tube that just went bad (low emission). Most tubes don't burn out; they deplete the electron-emitting layer from the cathode sleeve and even though they light up, their cathodes can't boil off enough electrons for the tube to conduct current. This may seem like it would be noticeable due to performance degradation over time, but often it is as abrupt as switching off a light bulb- the tubes have very wide operating ranges and will often only fail at a "tipping point" where they cannot operate any more. Recommend that you get your tubes tested, or line up a set of known-good substitutes that you can swap in and out, one at a time.
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:My guess is a bad connection from a chairside radio being bumped around.
:Cold solder joint, faulty volume control or a similar infuriating small detail.
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:Touching tube grid pins with a screwdriver or the DMM lead can sometimes help trace the problem to a specific area. Good Luck.
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Best Regards,
Bill Grimm
:Hi TB and Tom,
: It has been a treat reading how you, Tom, are walking through the basics here.
: I think the next step in this is to touch the cap of the 6Q7. Hear a bad hum? That indicates that signal can pass through that tube, the next stage and out the speaker.
: These symptoms indicate to me front end problems, though. This means I suspect that when you touch the 6Q7 grid cap it will hum.
: IF troubles seem to show up as dead quiet. You are getting noise. Touch the cap of the 6A6G. What happens then. Sometimes you get stations. That indicates front end problems.
: BEFORE YOU DO ANY OF THIS TOUCHING, make sure the chassis is not hot. Place an AC meter between it and ground. If it reads AC line current, don't touch. Also when doing this touch test don't touch anything else in the radio.
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:Best Regards,
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:Bill Grimm
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Your placement of the meter on the 6Q7G tube cap indicates signal going from there to out the speaker, also indicating that 8vac on the tube cap is unlikely. Could you mean 0.8vac?
Try recheking these. If it is really 8vac, this should be an easy miswiring to find.
Do you have any other equipment available? Do you have any other tubes around?
All the Beat,
Bill Grimm
I looked up your radio and it has voltages given for each tube pin. Regrettably the copy is quite muddy. I also didn't see the voltages for the grid caps, perhaps because they figured the reader would know they would be near zero.
Best Regards,
Bill Grimm
:Hi T.B.,
: Another thing to try, before I forget it,is something quite easy.
: Fire up the radio and turn out all the lights. Do any of the tubes have a blue glow? If it is the 25L6G don't worry about it, but if any of the others glow blue, this is a sign of gas in the tube.
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: I looked up your radio and it has voltages given for each tube pin. Regrettably the copy is quite muddy. I also didn't see the voltages for the grid caps, perhaps because they figured the reader would know they would be near zero.
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:Best Regards,
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:Bill Grimm
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:I will check for the blue Bill...
:Do you have another email address? I can send you a clearer copy of the pin voltages I found, and I will put what I am reading on mine...thanks everyone so muh for this help...I really wanna learn to master these things like all of you....
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::Hi T.B.,
:: Another thing to try, before I forget it,is something quite easy.
:: Fire up the radio and turn out all the lights. Do any of the tubes have a blue glow? If it is the 25L6G don't worry about it, but if any of the others glow blue, this is a sign of gas in the tube.
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:: I looked up your radio and it has voltages given for each tube pin. Regrettably the copy is quite muddy. I also didn't see the voltages for the grid caps, perhaps because they figured the reader would know they would be near zero.
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::Best Regards,
::
::Bill Grimm
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Send your voltage readings to bill All the Best, Bill Grimm