Power Transformer Assistance/I.D.

[barryman]

As this is my first post I will start with a disclaimer that I've read through the forums for weeks now and have gained a lot of knowledge so as not to ask questions that have been answered a hundred times before. That being said, I recently acquired a Baldwin Organ amp which housed 2 separate circuits; I was told that one was a 36 Watt and the other an 18 Watt. Each was run from this PT with their own respective OT's. I've separated the 18 Watt circuit and would like to transform the 36 Watt into the one this forum is dedicated to but I have some questions about the PT.

I've been able to determine what most of the wires are but would appreciate some clarification on the rest:

White/Red: terminates to ground. (HT CT?)
White/Blue: + side of 40mfd/450V filter cap (Heater CT?)
White: Connects to a diode - (voltage tap for the bias supply (AC voltage out)?
(2) Blue: Connect to two diodes which terminate to ground - (voltage tap for the bias supply (AC voltage out))?

Can you tell me if these are necessary or can I just cap them off (with the exception of the white/red wire which in the layout goes to ground via a 500ma HT fuse)?

Also, can anyone tell me if it would be ok to run only (4) El84's & (3) 12ax7's where the PT previously ran (6)el84's & (5) 12ax7's? The amp also housed a 5U4 rectifier. I'm not quite sure how to determine current draw or even where to begin looking for resources on how to do so. If anyone could point me in the right direction of some resources or answer my questions I would greatly appreciate it, thanks!


Please see the below pix for a reference of the amp where photos 1, 11-15 show the PT wires in question:

http://picasaweb.google.com/barrycasebe ... n1836Watt#

[57chevy]

I've been able to determine what most of the wires are but would appreciate some clarification on the rest:

White/Red: terminates to ground. (HT CT?)
White/Blue: + side of 40mfd/450V filter cap (Heater CT?)
White: Connects to a diode - (voltage tap for the bias supply (AC voltage out)?
(2) Blue: Connect to two diodes which terminate to ground - (voltage tap for the bias supply (AC voltage out))?

Can you tell me if these are necessary or can I just cap them off (with the exception of the white/red wire which in the layout goes to ground via a 500ma HT fuse)?

The wht/red probably is the HT CT, but you need to confirm this. Pull the 500ma fuse, then use your ohm meter to check for resistance between the wht/red wire and the wires connected to pins 4 and 6 of the 5U4. If you do have resistance and the two readings are the same/close, then you have identified the wht/red as the HT CT. Put the fuse back in.

As for the remaining four wires... Disconnect all four wires noting where they connect. Now use your ohm meter to check for resistance between any and all of these wires. Group together any wires that have resistance to each other. Next check each of the four wires for resistance readings to any of the other PT wires.

Once you have a clear idea of the wire resistance relationships to each other and to the rest of the PT, its time to make some AC voltage measurments. Pull the 5U4 and power up the PT. Measure AC voltages for the 4 wires.

Now you should know if you need the extra wires or not. There's a chance that the wht/blu, wht, and two blu wires are all common, but that's only a WAG at this point.

Another approach would be to decide what you need for the amp you're gonna build. Obviously you'll need B+ and filaments. Those should be easy to identify and should be in place already. That's really all you need to build a cathode biased amp. All other PT wires can be disconnected, taped up and tucked out of the way without even caring what they are for. And if you're gonna build a fixed bias amp, you can just use one side of the HT winding as the AC source for the bias supply.

[barryman]

Thanks so much for the info on testing voltages; I thought what you suggested was the right course of action but I wanted to be sure. Also, I don't think I really need to know what those other wires are but curiosity got the better of me. That and I'd rather know too much than too little about what I'm doing when it comes to working inside an amp. Cheers!

[57chevy]

Also, I don't think I really need to know what those other wires are but curiosity got the better of me. That and I'd rather know too much than too little about what I'm doing when it comes to working inside an amp.

Now that's some healthy thinking. If you have the amp's model number, or the organ's model number, you may even be able to find a schematic on the net.