Chicago Standard Transformer TF1A15YY C.S.T.C. 18227

Description

Revised 9/25/20 to clarify and include more information.
Manufacturer: Chicago Standard Transformer (Pre Stancor and Essex)
Military Specification Type: TF1A15YY
C.S.T.C. 18227 (Stamped in metal on bottom of each transformer)
B. & W. NO. 11053
Physical:
Hermetically sealed rectangular steel "can".
2.25" square x 3" tall.
3/8" mounting flange on two sides.
Approximate weight 2 lbs.
Shielding:
Not much. This is an output transformer.
Because they lack shielding, these transformers are not well suited to be used as microphone or MC phono input transformers.
Application:
SE plate to grid and/or line
Specifications printed on case:
Primary Impedance = 30,000 ohms
Primary DC current = 7ma max
Primary working voltage = 535v peak.
Secondary 1 Impedance = 67,000 Ohms, no dc
Secondary 2 Impedance = 200 ohms
Secondary 2 DC current = 5madc max
Maximum Level +5dBm*
*Elaboration by seller: 9.75vrms into primary (30k ohms when secondary load = 200 ohms).
Frequency response = 200hz to 3khz +-1dB.
Measured Parameters:
Primary inductance = 18.5Hy +-15%
Primary Resistance = 1.2K +-5%
Frequency response = 10hz to 30kHz +-1dB into 200 ohms from 600 ohms source.
Distortion =  0.15% THD+noise at 20hz for 25vrms (maximum level available from source) input to primary.
Note: 25vrms input to 30k ohms is equivlent to +13.2dBm
Voltage ratio, primary to secondary 2 =  12.25:1
Secondary 2 output impedance at 20hz with 600 ohm source driving primary = 50 ohms
Projected maximum mid-band power output: +28.75dBm/.75wrms (12.25vrms into 200 Ohms, 21.2vrms into 600 ohms),
single ended pentode (EL84 suggested) source with 250vdc plate supply.
BACK STORY
I bought 24 of these in 1973 from a surplus dealer in Mt. View, CA (Haltek). I still have 23 of them.
My intention has been to use them as output transformers in constructing close copies of RCA tube mic preamps for a 24 track resording system. Sigh....
They appeared, then, to be NOS. If so, they are still NOS, but I've been dragging them around with me for 47 years and they have gotten a bit dirty and scratched.
I have taken electrical measurements of them on several occasions with various laboratory grade test instruments and have kept them because of their excellent performance.
Going by the designation numbers, they were (well over) spec built for the US military and seemingly never listed in any general product catalog.
I have reached the point where I have accumulated SO much good stuff and have more projects lined up than I will ever be able to get to so it's time to liberate these treasures.
Other Possible Applications:
SE EL84 powered headphone amp.
Interstage and output transformers for tube hifi preamp.
Output transformer for tube MC preamp feeding a professional console line in or balanced line in on esoteric high fidelity premplifier.
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