>I purchased a pair of brand new Eimac 8877 tubes.
>The tubes are labled with indication: "YU-158".
>I there any difference?
Hi Werner...yes there is a difference. YU-158's are "specially
selected" for medical use 8877's.
I have found through testing over 20 8877's and 16 YU-158's
with date codes from the late 80's to the mid 90's (all new
tubes)that the power output of all 36 tubes was within 6%
between best and worst, but the grid current was 10% less
in the YU-158's.
My "tube tester" is a brand new RF Plasma Products
plasma generator that I didn't have the heart to chop up.
It operates on 13.56 mhz. The HV is 4000 volts, and
the filament voltage is 4.975 volts. Each tube is tested
without changing any controls, and its Ip, Ig, power output,
and ZSAC are recorded with a polaroid camera.
The 8877/YU-158 IMO must have a very close tolerance
criteria during assembly, as any two Tubes I have ever
had my hands on would qualify as a so called "matched pair!"
The YU-158 is also a good way to avoid getting your hands
on the bad vintages of 8877's that were made in the '80's
and early 90's. It is my understanding that the YU-158
nomenclature and "selection" process was Eimac's
successful attempt to restore its credibility with the MRI
manufacturers who were suffering from excessive 8877
failures in their machines.
Sorry for the BW, all....he asked what time it was, and I told
him how to build a watch!
(((73)))
Phil, K5PC
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