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Old 2nd May 2010, 02:47 AM   #1
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Default Help figuring which is the center tap???

Hello,
I just purchased this to build a 45 SET (see pic). The schematic on the side of this transformer shows a center tap but it does not designate which pin is actually the CT. In fact there are 10 pinouts on the bottom, all of which are accounted for on the schematic, none of which are shown to be the CT. There are no other pinouts anywhere on the transformer??? So where is the CT shown on the schematic???

Help!!!

Jeff

Last edited by jmillerdoc; 2nd May 2010 at 02:48 AM. Reason: add the pic
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Old 2nd May 2010, 02:49 AM   #2
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Default here is the pic for above

and the pic.....
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Old 2nd May 2010, 02:52 AM   #3
llwhtt is offline llwhtt  United States
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Check to see if it is connected to the bottom heater winding (gnd) and then check to see if it goes to the case or mounting lug.

Craig
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Old 2nd May 2010, 02:56 AM   #4
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I have a transformer similar to that one. Millitary surplus. You should find continuity from the HV winding to the case. The case is the CT. Make sure that the case is very well grounded, or it will be electrically HOT! A shocking situation.
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Old 2nd May 2010, 02:59 AM   #5
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Thanks, I am glad I asked before I just set this thing on my bench and started firing it ou and testing it with a DVM! It would have very well been a shocking revelation!

Damn these guys for not labeling it that way!
Jeff
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Old 2nd May 2010, 03:00 AM   #6
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Another question, how do I use the 5V winding since it appears to be a part of the other windings? Or is it actually a seperate winding?
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Old 2nd May 2010, 04:09 AM   #7
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Quote:
Originally Posted by jmillerdoc View Post
Another question, how do I use the 5V winding since it appears to be a part of the other windings? Or is it actually a seperate winding?
You can use it for a negative supply... only 10 mA rating, though...

There's an extra 6V winding - use it for a 6X5.
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Old 2nd May 2010, 04:55 AM   #8
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Quote:
Originally Posted by Tom Bavis View Post
You can use it for a negative supply... only 10 mA rating, though...

There's an extra 6V winding - use it for a 6X5.
It appears the 5V is a 2 amp rating, I think you might be referring to the other voltage, the 400V @10mA.
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Old 2nd May 2010, 01:16 PM   #9
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The 5 volt winding is connected to the 400 volt winding. All of the common 5 volt rectifier tubes have their 5 volt heaters (or filaments) connected directly to the cathode. This means that in order to use the 5 volt winding you are connecting the 400 volt tap to the cathode of the tube which will result in a negative voltage supply. This was not too uncommon in some millitary display applications including small oscilloscopes.

The usual trick of grounding the plates and taking the positive B+ output from the center tap won't work here since you will get 400 volts on the transformer case.

It does appear that to use this transformer you will need to use a 6 volt rectifier tube like the 6X4 or 6X5 to get a positive supply voltage.
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Old 2nd May 2010, 04:24 PM   #10
llwhtt is offline llwhtt  United States
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The McIntosh MI200 used this method to develop the bias voltage for the driver/output stage.

Craig
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