Those Sylvania's are 8cs7 double triodes, should be a t-6 1/2 bulb. Measure from the glass bottom to the top of tip (2 3/8" max) & a 7/8" O.D. (max). Tube is divided into two sections with section 1 being utilized as a oscillator, section 2 is the amplifier. Value nos $3 (used <$.10)
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