Quote:
Originally Posted by Phil Allison[_3_]
"flipper"
"Phil Allison"
UBT-1 is rated at 160mA on the primary...
** Yep - the total idle current is 110mA.
Did those 300Bs develope a dead short?
** According to the owner/builder - there was a flash / bang / wallop
event
and then a dead channel.
One dud 300B draws no bias current while the other draws waaaay to much,
the
UBT-1 has an open deep inside but shows no sign of shorted turns.
What has me intrigued, however, is the low THD figures at and near full
power PLUS the fact that 3H dominates.
The test results are far more like a PP class A triode amp than a SE one.
The 6SN7 is running at full gain ( about 18 times per half ) and there is
definitely NO negative feed back - in fact the two speaker windings have
been left floating.
Sounds like by either intent or serendipity the 300B and 6SN7 2'nd
harmonics are canceling.
** Bingo !!
Seems an eccentric Russian gent was responsible for the circuit design.
The owner has agreed to purchase another UBT-1 from the USA and new 300Bs
and send them to me.
Then I can hook the beast up to my own speakers ( 10 inch 3 ways plus active
sub ) for a listen.
...... Phil
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There was an article on 2H cancellation in SE amps published about 10 years ago, I think in Glass Audio. Used the curvature of the driver to cancel curvature in the OP Tride. One would think this possible at only one level on the output.
At the time I thought that might give rise to 4H, Etc thru harmonic multiplication. Another article by an Australian I recall did something similar by paralleling the ouputs of two seperaste SET amps in antiphase (for the 2H). I recall sending a copy to Patrick T at the time.
Probably somewhere in my pile, if so I will pass it on.
The WE data book shows 3H as well as 2H in all SET amplfiers.
Cheers to all, John