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PostPosted: Thu Sep 01, 2011 10:47 am 
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I have a question regarding the output transformer:
Ok, the OT Primary brown lead goes to pin7 V5 and the blue to pin7 V4. What would be if it is the other way around, it the brown goes to pin7 V4 and the blue to v7 pin5?
Any difference?


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PostPosted: Thu Sep 01, 2011 12:26 pm 
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Might be a bit unstable.

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PostPosted: Thu Sep 01, 2011 12:49 pm 
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Buy swapping those lines you've shifted the output by 180 degrees. Any signal that gets coupled from the o/p to the preamp may add where it used to cancell so you might get oscillations. It's not a hugh issue since the 18s do not have NFB( negative feeback). If you get squeels ect. switching those lines back might fix the prob.

Stew


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PostPosted: Thu Sep 01, 2011 7:10 pm 
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Thanks for your replies guys!
But how do you know which primary goes to which anode? Ok, the center tap of the primary windings goes to B+, but if it was another output transformer and different colors of the 2 primaries which you have to connect to the anodes on v4 and v5, how do you determine which primary goes where?


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PostPosted: Fri Sep 02, 2011 5:55 pm 
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I have been searching, but still have not found anything. Mostly people say, if it squeals then you need to turn the amp off and switch the plate leads. But there has to be another way.
If there are some of you who do not know that the primaries which are soldered to pin 7 of the power tubes in the 18 Watt are called plate leads, now you know. So, I am basically looking how to identify plate leads on an output transformer, so you know which plate lead goes to which output tube pin.


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PostPosted: Fri Sep 02, 2011 9:11 pm 
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Unless you know how they mechanical wound the OT and which way the windings are and which is the outer winding the guess and check method is the best way.

On my builds if I am using a new OT to me I let the wires have a bit of slack when I wire them in. Then if it does squeak (positive feedback) I can easily reverse.

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PostPosted: Sat Sep 03, 2011 10:39 pm 
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And if the amp doesn't take negative feedback from the OT secondary, it doesn't actually matter which way round you connect the OT primary.

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