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Old 8th February 2009, 03:26 AM   #1
WRyan is offline WRyan  United States
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Default Transformer Polarity

Hello,

In regards to the following output transformer, I have a few questions:

http://www.tubesandmore.com/cemirror...50c_wiring.gif

Single Ended environment:

On the secondary side, which gets connected to speaker positive and which gets connected to speaker negative? I thought black was negative, but looking at the diagram, there is a dot and black is labeled (Com).

On the primary side, which gets connected to the plate and which gets connected to power supply? I have blue connected to plate and red connected to power supply.

I bet I mixed something up because when I connect the negative feedback loop to speaker jack positive (as schematic shows), I get oscillation.

Please let me know if I messed up the polarity of the transformer wiring.

Thanks!!!
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Old 8th February 2009, 03:35 AM   #2
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Default Re: Transformer Polarity

Quote:
Originally posted by WRyan
Single Ended environment:

On the secondary side, which gets connected to speaker positive and which gets connected to speaker negative? I thought black was negative, but looking at the diagram, there is a dot and black is labeled (Com).
How many secondary taps? "Com" is the ground side of the secondary, usually important if there are more than one tap-off.

Quote:
I bet I mixed something up because when I connect the negative feedback loop to speaker jack positive (as schematic shows), I get oscillation.
On the primary side, it makes no difference. If you have oscillation, simply reverse the connections at the primary. It doesn't make any difference since the OPT winder doesn't know how many gain stages there are, and what the output phase will be.
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Old 8th February 2009, 03:48 AM   #3
WRyan is offline WRyan  United States
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Thanks Miles.

There is only one secondary tap 4ohms (well, technically 3.2).

I wonder if I could accomplish the same thing by switching the secondary side orientation. I only ask because it is easier access.

Thanks again!!!
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Old 8th February 2009, 04:55 AM   #4
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Quote:
Originally posted by WRyan
There is only one secondary tap 4ohms (well, technically 3.2).

I wonder if I could accomplish the same thing by switching the secondary side orientation. I only ask because it is easier access.
Since there's just the one secondary, you can reverse the connections there.
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Old 8th February 2009, 08:53 AM   #5
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It seems the usual convention is:
Red= B+
Blue= Tube Anode
Black(com)= Speaker Ground
Yellow= Speaker positive/hot
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Old 8th February 2009, 01:51 PM   #6
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There can be no convention for the primary. As Miles says, the transformer maker can't know whether there is an odd or even number of gain stages in the NFB loop.
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