Power Transformer Problems

10/18/2012 2:59:30 PMJohnny

A friend is trying to rebuild this U.S. Radio & Television Co. model 99A. I can't answer his question. Maybe you can help. Below is a picture of the transformer and some resistance readings. All looks good except the open plate winding. Biggest question is... What is one side of the primary doing connected to the CT of the 280 plates and the 100K resistor in series with a .02ufd cap to chassis ground. I don't know what someone has done here but I suggested finding another transformer or a rewind.

Hope I made this pic work.

Thanks,
Johnny

10/18/2012 3:53:34 PMEdd

Sir Johnny . . . . .

Since apparently, you are taking measuring with the transformer STILL in circuit . . . not to worry on the 100 K and .02 capacitance readings .

If you consult the schematic you will find the .02 capacitance presence being to the right, about half way towards the speaker.

The 100 K of resistance is from a resistor located just above the speaker field coil , using ye olde 100M marking /designation procedure at that tyme.

Looks like the HV secondary of the T-former is open . . . .but strange that you did not at least read some lower ohms continuity on at least one ohmmic metering fron the HV center tap to EITHER of the HV side windings ends.

On the CHEEP . . . initially research the possibility of finding a salvage t-former from:

> > > Teeeee-Former HOT Linking . . sssssssssssstttt ! < < <

73's de Edd

Rule of defactualization:

Initial information tends to deteriorate quasi fractionally, when gravitating upward through bureaucracies.

:A friend is trying to rebuild this U.S. Radio & Television Co. model 99A. I can't answer his question. Maybe you can help. Below is a picture of the transformer and some resistance readings. All looks good except the open plate winding. Biggest question is... What is one side of the primary doing connected to the CT of the 280 plates and the 100K resistor in series with a .02ufd cap to chassis ground. I don't know what someone has done here but I suggested finding another transformer or a rewind.
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:Hope I made this pic work.
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:Thanks,
:Johnny
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10/18/2012 4:31:58 PMJohnny

Thanks Edd! Good hearing from you again. I did see the 100K going to the CT of the HV 280 winding of the T-former. But the other end of it goes to a .5ufd to ground & to the cathode of the 224. The 100K and the .05 is the bias for that cathode? The t-former is out of the radio and isolated from all circuitry. The .02ufd is on the schematic and is in parallel with the 300 ohm section of the candohm. In fact mounted right on the candohm. But another .02 was mounted directly on the t-former with another 100K 1/2W and went from one end of the 100K to chassis ground.

Sorry for my bad drawing. Have two computers and my editing program is on my machine that's having a problem of it's own. Had to draw by hand and obviously I'm no artist.

The 280 plate winding is open reading across it. But one leg of the 280 plate winding does read 80 ohms to the CT. As stated... sorry for the poor drawing but that's what that 80 ohms on my drawing is supposed to indicate. One leg of the 280 plate is open to the CT & one leg reads the 80 ohms to the CT but across the whole 280 plate winding reads open. I've repeated myself.

What concerned me the most was the connection between the primary side of the t-former to the CT of the secondary 280. This can't be correct and I believe is what caused the 280 HV winding to open. Would you agree?

Johnny

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:Sir Johnny . . . . .
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:Since apparently, you are taking measuring with the transformer STILL in circuit . . . not to worry on the 100 K and .02 capacitance readings .
:
:
:If you consult the schematic you will find the .02 capacitance presence being to the right, about half way towards the speaker.
:
:
:The 100 K of resistance is from a resistor located just above the speaker field coil , using ye olde 100M marking /designation procedure at that tyme.
:
:
:Looks like the HV secondary of the T-former is open . . . .but strange that you did not at least read some lower ohms continuity on at least one ohmmic metering fron the HV center tap to EITHER of the HV side windings ends.
:
:
:On the CHEEP . . . initially research the possibility of finding a salvage t-former from:
:
:
:
:
:> > > Teeeee-Former HOT Linking . . sssssssssssstttt ! < < <
:
:
:
:
:
: 73's de Edd
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: Rule of defactualization:
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:Initial information tends to deteriorate quasi fractionally, when gravitating upward through bureaucracies.
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::A friend is trying to rebuild this U.S. Radio & Television Co. model 99A. I can't answer his question. Maybe you can help. Below is a picture of the transformer and some resistance readings. All looks good except the open plate winding. Biggest question is... What is one side of the primary doing connected to the CT of the 280 plates and the 100K resistor in series with a .02ufd cap to chassis ground. I don't know what someone has done here but I suggested finding another transformer or a rewind.
::
::
::
::Hope I made this pic work.
::
::Thanks,
::Johnny
::
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