05-07-2021, 09:50 AM
The input primary side: Red is B+, Blue is Plate. Output secondary side: Green is Grid and Black is B- or C- or ground...
Established that the primary and secondary are fine by using resistance.
What is supposed to happen is that the primary does not phase shift the secondary. That is one of the reasons for color coding the other to identify primary and secondary start & finish. The reason phase shift must not happen is stray coupling via C- or B+ can feed back audio signals and re-enforce setting up an oscillation.
There is no phase shift normally for this installation....
If you want to know if the phase is correct. You will need an audio generator that can be set for 2khz and variable voltage from .25 to 5 volts.
Need a carbon resistor of somewhere from 10K to 50k 1/4 W.
Two channels of the scope, set to display 4 cycles of the 2khz., +trigger on ch1 set at .1 volt., no storage.
Move trace 1 to upper area and trace two to lower.
Remove any connections to the A-K at the batteries, remove the detector and the two audio tubes.
I tried to work out not disconnection the transformers, but it will be better to disconnect the transformers.
Take one primary lead and one secondary lead (the current plate and grid wires) ti the primary connect the resistor, the resistor to the generator signal lead. Connect the common grounds to the B- of the transformer and the C- of the transformer.
Connect ch1 to the plate lead where the resistor is and connect Ch2 to the grid lead. The scope should see the transformer with no resistors. The resistor is to isolate the impedance of the generator.
Now jump the common ground lead to C- of the transformer. Bring up the generator to one volt by viewing the scope, be sure the trigger is coupled to channel one so it takes off at the same time. You should see channel 1 and two in phase. Both rising/falling in step, OR falling depending if (-) trigger was selected and coupled correctly.
If the transformer output is out of phase the signal will be 180 degrees out. falling or rising opposite of the other.
You will have to adjust the amplitude of the secondary..
Set the generator to create an envelope of one division on channel one. set channel two to the same division. The resultant signal on the wave form will be the amount of voltage gain from the transformer.
I think you will see at least 3:1 but could be as much as 5:1. If you change the frequency to say 1khz the ratio may change, will be lower ratio at 440hz. This is the "roll-off" of the transformer.
If the signal is in phase then simply re-solder the connections. If it is not reverse either the pair of primaries or the pair of secondaries, not both. That will correct the phase.
Do both transformers as the colors were lost on each.
The radio should function normally, with in phase connections.
If the radio howls either there is a phase mistake or the radio requires that one of the transformers has to invert the phase.
If that is so, then select either transformer that has long enough wires to swap just one pair of wires. on one winding. Do not swap twice...
If you note that at 2khz one transformer has a higher ratio than the other it would be best to place that transformer as the first audio transformer, the volume will of the detector will be improved when used for DX.
The cotton braided wire covering is a solid color coded, no tracer, but the asphalt potting stains it badly very difficult to see the color even if using a solvent to wash out the tar.
GL Chas
Established that the primary and secondary are fine by using resistance.
What is supposed to happen is that the primary does not phase shift the secondary. That is one of the reasons for color coding the other to identify primary and secondary start & finish. The reason phase shift must not happen is stray coupling via C- or B+ can feed back audio signals and re-enforce setting up an oscillation.
There is no phase shift normally for this installation....
If you want to know if the phase is correct. You will need an audio generator that can be set for 2khz and variable voltage from .25 to 5 volts.
Need a carbon resistor of somewhere from 10K to 50k 1/4 W.
Two channels of the scope, set to display 4 cycles of the 2khz., +trigger on ch1 set at .1 volt., no storage.
Move trace 1 to upper area and trace two to lower.
Remove any connections to the A-K at the batteries, remove the detector and the two audio tubes.
I tried to work out not disconnection the transformers, but it will be better to disconnect the transformers.
Take one primary lead and one secondary lead (the current plate and grid wires) ti the primary connect the resistor, the resistor to the generator signal lead. Connect the common grounds to the B- of the transformer and the C- of the transformer.
Connect ch1 to the plate lead where the resistor is and connect Ch2 to the grid lead. The scope should see the transformer with no resistors. The resistor is to isolate the impedance of the generator.
Now jump the common ground lead to C- of the transformer. Bring up the generator to one volt by viewing the scope, be sure the trigger is coupled to channel one so it takes off at the same time. You should see channel 1 and two in phase. Both rising/falling in step, OR falling depending if (-) trigger was selected and coupled correctly.
If the transformer output is out of phase the signal will be 180 degrees out. falling or rising opposite of the other.
You will have to adjust the amplitude of the secondary..
Set the generator to create an envelope of one division on channel one. set channel two to the same division. The resultant signal on the wave form will be the amount of voltage gain from the transformer.
I think you will see at least 3:1 but could be as much as 5:1. If you change the frequency to say 1khz the ratio may change, will be lower ratio at 440hz. This is the "roll-off" of the transformer.
If the signal is in phase then simply re-solder the connections. If it is not reverse either the pair of primaries or the pair of secondaries, not both. That will correct the phase.
Do both transformers as the colors were lost on each.
The radio should function normally, with in phase connections.
If the radio howls either there is a phase mistake or the radio requires that one of the transformers has to invert the phase.
If that is so, then select either transformer that has long enough wires to swap just one pair of wires. on one winding. Do not swap twice...
If you note that at 2khz one transformer has a higher ratio than the other it would be best to place that transformer as the first audio transformer, the volume will of the detector will be improved when used for DX.
The cotton braided wire covering is a solid color coded, no tracer, but the asphalt potting stains it badly very difficult to see the color even if using a solvent to wash out the tar.
GL Chas
Pliny the younger
“nihil novum nihil varium nihil quod non semel spectasse sufficiat”
