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Old 7th December 2010, 01:54 AM   #1
HFGuy is offline HFGuy  Canada
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Join Date: Sep 2004
Location: Toronto, Ontario
Default A quick tube matching question

hey folks,

I bought 2 pairs of matched kT88 tubes many years ago. I now have 4 tubes and am not sure which of the 4 belong to which pair. I am not sure if it is more important to match the primary current or the transductances. The 4 tubes have the following spec'

Ip = 46 gm = 4300
Ip = 51 gm = 4500
Ip = 45 gm = 4800
Ip = 50 gm = 4700
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Old 7th December 2010, 10:07 AM   #2
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Join Date: Feb 2010
Even non-matched tubes can be used to build a very good performing HiFi-amplifier.

This requires to apply an individual fixed bias arrangement so that the quiescent currents of each tube can be adjusted to same value.

Also the phase splitter should have adjustement for both output driving signals. Then you can balance also the AC-part of the tubes.
However to perfectly adjust this you need a distortion meter.

Concerning your original question; I would put Ip = 46 / 45 as pairs and similarly Ip = 50 / 51 .
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Old 7th December 2010, 10:19 AM   #3
DF96 is offline DF96  England
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Join Date: May 2007
I would say first match on current, then match on gm. On that basis I would agree with artosalo's pairing.
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Old 10th December 2010, 07:30 PM   #4
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Join Date: Jul 2008
If you match by Ip, both tubes in each pair are within 3%, which is good.
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