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(Click here for a list of transformers, ratings, pictures, and data.)
Alum Rock designs its tranformers for performance, appearance, reliability, minimal heat dissipation, and minimal stray field or suseptibility to stray fields. Alum Rock places little emphasis on minimizing size, weight, or cost. Units which carry direct current generally have internally gapped cores. All transformers and inductors are vacuum-impregnated. High voltage transformers such as output transformers go through three separate potting cycles. A Biddle corona testing facility is used to measure the corona current for all high voltage units. Output transformers are tested for corona current at 1,200 Vrms + 2,000 VDC.
All transformers are wound and impregnated for Alum Rock by the Robert M. Hadley Company in Ventura, California. This third-generation company has a long history of supplying high quality transformers to the military and aerospace industry, and is now in the field of audio transformers through Alum Rock Technology.
In addition to its interstage transformer, which has a primary inductance of 150 H, Alum Rock has three sizes of output transformers for class A single-ended service:
Primary impedance stated above is the turns ratio squared times 8 ohms. Plate current is the nominal operating point, not the maximum. (larger photo of interstage and above three output transformers.)
Additionally, Alum Rock makes a plate transformer, high voltage inductor assembly, and a bias and 866A filment transformer, as well as 304TL filament transformers and matching inductors. These filament transformers are capable of supplying 10 VDC at up to 26 A. Alum Rock offers these transformers and inductors in sets.