Help figuring which is the center tap???

jmillerdoc · 01:48 AM

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

jmillerdoc · 2nd May 2010, 01:49 AM

and the pic.....

llwhtt · 2nd May 2010, 01:52 AM

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

tubelab.com · 2nd May 2010, 01:56 AM

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.

jmillerdoc · 2nd May 2010, 01:59 AM

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

jmillerdoc · 2nd May 2010, 02:00 AM

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?

Tom Bavis · 2nd May 2010, 03:09 AM

Quote:

Originally Posted by jmillerdoc

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.

jmillerdoc · 2nd May 2010, 03:55 AM

Quote:

Originally Posted by Tom Bavis

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.

tubelab.com · 2nd May 2010, 12:16 PM

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.

llwhtt · 2nd May 2010, 03:24 PM

The McIntosh MI200 used this method to develop the bias voltage for the driver/output stage.

Craig

2nd May 2010, 01:47 AM	#1
jmillerdoc diyAudio Member Join Date: Mar 2009 Location: Lawton, OK, USA	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 01:48 AM. Reason: add the pic

2nd May 2010, 01:56 AM	#4
tubelab.com diyAudio Member Join Date: Jul 2005 Location: South Florida	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. __________________ Too much power is almost enough! Turn it up till it explodes - then back up just a little.

2nd May 2010, 12:16 PM	#9
tubelab.com diyAudio Member Join Date: Jul 2005 Location: South Florida	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. __________________ Too much power is almost enough! Turn it up till it explodes - then back up just a little.

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
No center tap Help	FastEddy	Power Supplies	57	19th April 2010 07:01 PM
Center-tap to ground?	cbutterworth	Power Supplies	0	17th January 2007 03:41 PM
Gainclone and center tap	marcus7601	Chip Amps	2	29th November 2006 02:12 PM
transformer with no center tap	traw	Parts	0	3rd June 2006 02:36 AM
Missing center tap	Herrmann	Everything Else	3	30th April 2002 06:54 PM

2nd May 2010, 01:52 AM	#3
llwhtt diyAudio Member Join Date: Jun 2008	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

2nd May 2010, 01:59 AM	#5
jmillerdoc diyAudio Member Join Date: Mar 2009 Location: Lawton, OK, USA	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

2nd May 2010, 02:00 AM	#6
jmillerdoc diyAudio Member Join Date: Mar 2009 Location: Lawton, OK, USA	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?

2nd May 2010, 03:24 PM	#10
llwhtt diyAudio Member Join Date: Jun 2008	The McIntosh MI200 used this method to develop the bias voltage for the driver/output stage. Craig

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)

New To Site?	Need Help?
Register to Participate Search Privacy Statement Contact Us	Frequently Asked Questions Did you forget your password? Mark Forums Read