question for a 4xKT88 PP amp

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Just finished a 4xKT88 push pull amp and I'm doing some measurements. Anode voltage is 550V and screens at 400V. Phase inverter is an AC coupled LTP with a 12AT7 and there's negative feedback at around 6db. OPT is a Hammond 1650T.

What I can't understand is that I measure different watts at each tap of the secondary. Around 150W at 8 ohm secondary tap and around 200W at 4 ohm tap. For dummy load I have two 8R2 ohm resistors rated at 150W. One for the 8 ohm measurement and two in parallel for the 4 ohm measurement.

Any ideas why I measure different watts? What am I missing here?
 
I hate taps, always some design problem.

Btw, have you wired like this?

Secondary Connections (Due to the unique interleaving of the windings BOTH secondary windings must be engaged to meet specifications)
sec2.gif
If those wirins are not equal, then currents may flow between windings (inner/outer side bobbin could make difference)
 
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hpeter, yes of course.

I have done this wiring for the 4 ohm,
sec1.gif


and this for the 8 ohm,
sec2.gif


With a heavy duty toggle switch I select each tap.

If those wirins are not equal, then currents may flow between windings (inner/outer side bobbin could make difference)
Yes but in both cases, 4 ohm or 8 ohm, the windings Grn/Yel - Blk/Yel and Grn - Blk are in parallel. I can't understand.

Unless, with the extra winding Grn/Yel - Yel is not exactly 8 ohm or the parallel windings are not exactly 4 ohm. Maybe I'll measure the ratio in both cases if this is the only reason I measure different output watts.
 
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