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FA: UTC HA-107 AUDIO INTERSTAGE TRANSFORMER (Fully-Tested)

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Mar 15, 2012, 4:18:56 AM3/15/12

Replacing Lundahl interstage transformer with UTC HA-107 was a big improvement. Permalloy

cores are inherently more linear than silicon steel. They may be not the best choice for

output transformer due to saturation issue, but for interstage use they are unbeatable.
HA-107:

15+15 K primaries
45+45 K secondaries
20-20,000 Hz 3 dB
Pmax 200 mW
No unbalanced DC
Weight about 4 lb

The core in these transformers is supermalloy (or hypermalloy, as UTC called it). It is 80%

Ni alloy annealed in hydrogen atmosphere to achieve the highest mu (about 20,000 compared to

10,000 of 45% Ni permalloy and 5,000 of silicon steel). High permeability allows achieving

the same inductance with fewer turns, thus decreasing stray inductance and winding

capacitance. HA-107 has two layers of shielding, external mu metal and internal copper.

Separate windings allow independent biasing of output tubes.

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