Desperate Milton.
It is possible that if you rewired the set, there could have been a miswire to begin with before you obtained the set. Perhaps a wire was missing and you did not realize this, so you left it missing. Also check unusual things like the trimmer condensers in the IF transformers. Open the transformers and disconnect the condensers from the coils, one at a time. Check to see if the condensers have shorts or leakage (leakage is unlikely unless the condensers are covered in dirt). Check for leakage from either coil of each IF transformer to its case with the transformer assembled. Check for fluke problems. You have to think beyond simple component failure and consider unusual problems. Check tube sockets for shorts to the chassis or between terminals. Check to see that all tube sockets have their required contacts--the ones needed for contact to the used tube elements--some manufacturers omit contacts for unused tube pins.
Thomas
Check items that Thomas mentioned but more information would help? How have you determined there is a short? Do you have plate voltages on tubes? Is there any sound out of the speaker? Is a part overheating?
Norm
:When checking for shorts, the best way to do so is to do an element to element test. Each tester has a different method for this, and some testers are not capable of doing this. If you replaced all of the tubes with new ones, though, then you do not likely have a short, because it isn't too likely that another set of tubes would have the exact same problem.
:
:It is possible that if you rewired the set, there could have been a miswire to begin with before you obtained the set. Perhaps a wire was missing and you did not realize this, so you left it missing. Also check unusual things like the trimmer condensers in the IF transformers. Open the transformers and disconnect the condensers from the coils, one at a time. Check to see if the condensers have shorts or leakage (leakage is unlikely unless the condensers are covered in dirt). Check for leakage from either coil of each IF transformer to its case with the transformer assembled. Check for fluke problems. You have to think beyond simple component failure and consider unusual problems. Check tube sockets for shorts to the chassis or between terminals. Check to see that all tube sockets have their required contacts--the ones needed for contact to the used tube elements--some manufacturers omit contacts for unused tube pins.
:
:Thomas
Maybe I am just repeating the obvious, but one of the things I do is to just start measuring voltages and looking for unusual or unexpected levels at unexpected places.
I just start at the RF end and work my way toward the output end. Measure plate voltages and other various points between stages. Maybe you don't know what all the voltages should be precisely, but you probably have a good idea of what is at least reasonable.
Keep moving along in the circuit and something should eventually show up. When a voltage level is measured that does not seem correct, the problem is somewhere close by.
The schematic for the H-126 comes with a handy "Voltage and Current Table" Measure each of these points to see if they are all within 20% as stated on the schematic.
There are also notes in this schematic regarding circuit changes in production for the H-126. See Riders pages 15-10 and 20-15. The changes affect the voltages that will be measured throughout the radio.
Maybe you need a different number output tube. The schematic calls for a 35A5 -BUT- the note says that in late production runs a 35L6GT was used and that the tubes bases and connections were different. In other words, the tubes are electrically similar but NOT interchangeable in the same circuit. Some of the other production changes were not insignificant either.
Can you verify that the circuit and the schematic are in agreement or that any of the referenced changes were implemented? It is possible that this is not just a single point failure.
I apologize if I am just going over old ground that you have already traveled.
Randy
:Milton,
:
:Maybe I am just repeating the obvious, but one of the things I do is to just start measuring voltages and looking for unusual or unexpected levels at unexpected places.
:
:I just start at the RF end and work my way toward the output end. Measure plate voltages and other various points between stages. Maybe you don't know what all the voltages should be precisely, but you probably have a good idea of what is at least reasonable.
:
:Keep moving along in the circuit and something should eventually show up. When a voltage level is measured that does not seem correct, the problem is somewhere close by.
:
:The schematic for the H-126 comes with a handy "Voltage and Current Table" Measure each of these points to see if they are all within 20% as stated on the schematic.
:
:There are also notes in this schematic regarding circuit changes in production for the H-126. See Riders pages 15-10 and 20-15. The changes affect the voltages that will be measured throughout the radio.
:
:Maybe you need a different number output tube. The schematic calls for a 35A5 -BUT- the note says that in late production runs a 35L6GT was used and that the tubes bases and connections were different. In other words, the tubes are electrically similar but NOT interchangeable in the same circuit. Some of the other production changes were not insignificant either.
:
:Can you verify that the circuit and the schematic are in agreement or that any of the referenced changes were implemented? It is possible that this is not just a single point failure.
:
:I apologize if I am just going over old ground that you have already traveled.
:
:Randy
:
Thomas
Now, some body ask me if some component runs hot, the 1500 ohm resistor #35 in riders schema goes very hot(turns red).
The radio makes Hum that increases or decreases with the volume control. If you touch the center lug of the volume control it makes a loud in the speaker.
I attach my signal generator at the given points for IF alignment but I cant hear any signal even turning it to the maximum and moving the setting of the signal generator from side by side throug all the dial.
I check and recheck twice against the schema and I cant found any wire placed in wrong place.
Respect the possibility that this unit uses the 50L6 instead the 35A5, the units with 50L6 have code letter "C" stamped in chassis and this unit haven't.
Milton.
:True that! Voltages tell a lot.
:
:Thomas
Measure the grid voltages for the 12SK7 tube, pins 3, 4, and 6. Verify pin 1 is grounded.
You mentioned earlier that you replaced all of the resistors. Did you replace #35 with a 1 watt (or greater) resistor? The others can all be 1/2 watt but this one has to be at least 1 watt. Check to see if it is still 1500 ohms and then measure the voltage drop across this resistor. If it was turning red it may not be 1500 ohms anymore.
If you still have any paper caps in there, I would replace them even if they measure good. And don't be fooled by paper caps hiding inside molded black plastic. They are still paper caps.
Randy
:Ok guys, I have Sams Photofact schematics and Riders Schematic for this radio, yes, both have a handy chart with voltages and resistances, I measured the plate voltages and this are the results:
: 35A5 - 110V - 120V
:12SJ7 - 13V - 28V
:12SF7 - 15V - 81V
:12SA7 - 15V - 81V
:12SK7 - 15V - 35V
:Left are my measures right are schematic values.
:
:Now, some body ask me if some component runs hot, the 1500 ohm resistor #35 in riders schema goes very hot(turns red).
:The radio makes Hum that increases or decreases with the volume control. If you touch the center lug of the volume control it makes a loud in the speaker.
:I attach my signal generator at the given points for IF alignment but I cant hear any signal even turning it to the maximum and moving the setting of the signal generator from side by side throug all the dial.
:I check and recheck twice against the schema and I cant found any wire placed in wrong place.
:Respect the possibility that this unit uses the 50L6 instead the 35A5, the units with 50L6 have code letter "C" stamped in chassis and this unit haven't.
:Milton.
::True that! Voltages tell a lot.
::
::Thomas
Any chance the second electrolytic cap is reversed?
Norm
:Milton,
:
:Measure the grid voltages for the 12SK7 tube, pins 3, 4, and 6. Verify pin 1 is grounded.
:
:You mentioned earlier that you replaced all of the resistors. Did you replace #35 with a 1 watt (or greater) resistor? The others can all be 1/2 watt but this one has to be at least 1 watt. Check to see if it is still 1500 ohms and then measure the voltage drop across this resistor. If it was turning red it may not be 1500 ohms anymore.
:
:If you still have any paper caps in there, I would replace them even if they measure good. And don't be fooled by paper caps hiding inside molded black plastic. They are still paper caps.
:
:Randy
:
:
::Ok guys, I have Sams Photofact schematics and Riders Schematic for this radio, yes, both have a handy chart with voltages and resistances, I measured the plate voltages and this are the results:
:: 35A5 - 110V - 120V
::12SJ7 - 13V - 28V
::12SF7 - 15V - 81V
::12SA7 - 15V - 81V
::12SK7 - 15V - 35V
::Left are my measures right are schematic values.
::
::Now, some body ask me if some component runs hot, the 1500 ohm resistor #35 in riders schema goes very hot(turns red).
::The radio makes Hum that increases or decreases with the volume control. If you touch the center lug of the volume control it makes a loud in the speaker.
::I attach my signal generator at the given points for IF alignment but I cant hear any signal even turning it to the maximum and moving the setting of the signal generator from side by side throug all the dial.
::I check and recheck twice against the schema and I cant found any wire placed in wrong place.
::Respect the possibility that this unit uses the 50L6 instead the 35A5, the units with 50L6 have code letter "C" stamped in chassis and this unit haven't.
::Milton.
:::True that! Voltages tell a lot.
:::
:::Thomas
Thomas
:The 35A5 will not make connection in the 35L6 socket, and the 35L6 will not fit in the 35A5 socket. The tubes would not light if a 35A5 was in the 35L6 socket anyway. Its filament connections are at pins 1 and 8. 1 and 8 on the 35L6 are the shield, if any, and the cathode, respectively, and so there is no chance of short or filaments lighting.
:
:Thomas
:
:
If pin 3 on the 12SK7 tube is showing 0 volts, then there has to be something wrong between that pin and the radio side of your switch (not the supply side). Check for continuity between those 2 points. It ought to read like a dead short between the two. Whatever voltage is coming out of your switch ought to also be present at pin 3 on that tube.
If continuity between these points is good, then I would next be concerned with cap C19. If it is leaking to ground, that would also have an affect on your electrolytics which might explain why that 1500 ohm resistor is heating up so much.
Randy
:Well, lets go by order first the voltages onthe 12SK7:
:pin 3-0V pin 4-15V pin 6-15V and yes pin 1 is tied to chassis.
:resistor #35 is 1487 ohms altough the overheating.
:elctrolitic caps measure good and are placed correct (anyway I will change them tonight)
:Good point that Thomas mentioned, the 50L6 and 35A5 are incompatible.
:Milton.
:
::The 35A5 will not make connection in the 35L6 socket, and the 35L6 will not fit in the 35A5 socket. The tubes would not light if a 35A5 was in the 35L6 socket anyway. Its filament connections are at pins 1 and 8. 1 and 8 on the 35L6 are the shield, if any, and the cathode, respectively, and so there is no chance of short or filaments lighting.
::
::Thomas
::
::
Also, if C19 was to become leaky, all it would do is leak voltage to the chassis. This is not "ground". It is simply the chassis. Unless the chassis was then grounded, which it should never be, no problem would exist. The chassis is otherwise isolated from all direct current flow within the radio. Do not take DC voltage readings from the chassis. Take them from the line switch.
Thomas
Randy
:There is nothing wrong with pin 3 of the 12SK7 tube showing zero volts. All readings should be taken from the radio switch, which is B- as far as the DC supply is concerned. Pin 3 of the 12SK7 tube (as well as its cathode) is connected to B-, which is the switch. Yes, it should be like a dead short between pin 3 and the switch. You should not see any voltage here.
:
:Also, if C19 was to become leaky, all it would do is leak voltage to the chassis. This is not "ground". It is simply the chassis. Unless the chassis was then grounded, which it should never be, no problem would exist. The chassis is otherwise isolated from all direct current flow within the radio. Do not take DC voltage readings from the chassis. Take them from the line switch.
:
:Thomas
Thomas
:We all have fried brain moments. I could point out several of my own on here. I'd rather not, though. Sometimes when I get home from work at 7 in the morning and I make a response, I have a fried brain moment.
:
:Thomas
You can try to measure the resistance in each half of each IF transformer and compare the measured values against the resistance table on the schematic to try to identify the primaries and secondaries. Although the difference in going from 26 to 27 ohms might be a little hard to distinguish.
Since you have already provided the plate voltages for the different tubes, why not go the rest of the way and post the values for the grid voltages (Sg from the table) also. Post the output of the rectifier too. Might not help but it couldn't hurt.
Randy
:The only connection to chassis is by the C19 cap and a 330K resistor, I measure the resistor and it is of the correct value and the C19 is a new .25 cap that tested good.
:I replace new electrolytics to see what happen but this doesnt change anything.
:Now I have a theory, the IF transformers have a primary and secondary. but ¿what is primary and secondary? the one up or down????.
:If the connections were reversed I mean, the pri insted of sec and sec instead of pri. does the radio works anyway?.
:I check the transformers for shorts but nothing.
:Thats why I was wondering that a tube were the responsible of this.
:Milton
::SO, Has he grounded the chassis??
::
::
::
:::We all have fried brain moments. I could point out several of my own on here. I'd rather not, though. Sometimes when I get home from work at 7 in the morning and I make a response, I have a fried brain moment.
:::
:::Thomas
Thomas
Milton.
:Grid voltages will definitely help as will all the others. Try to connect the IF coils exactly where they were originally. If you never tampered with them, then they are likely in their correct places. If they vary by only 1 ohm, then there is not much trouble in connecting them in reverse, but it is still somewhat critical as I have found in radios. It will affect selectivity to some degree. If there is a great difference in their impedances, each might have a different sized trimmer, and so in this case it is very critical that they be connected properly. If you are using a good meter, you should be able to tell which coil is which even if they are different by only one ohm. The other thing you want to look for is shorts between the coils or shorts in the trimmer condensers (coil disconnected from trimmer should yield infinite resistance). Each coil should be connected to its trimmer and set of wires properly. Reversing the leads of one coil can sometimes affect radio performance. If the coils are wound in a spiral, the outside wire of each should go to say B- and B+, and the inside wire of each should go to the plate of the first tube and the grid of the next tube. If wound in a helix, then use the top and the bottom of the coil as a reference. Usually AM IF coils are so large that they are wound in a spiral (from inside to outside in circumfrences of increasing diameter). In case you are confused now, a helix is actually what binds your notebook together. Using the term spiral is incorrect. A spiral changes in diameter.
:
:Thomas