There's quite a story behind this brand. They don't actually make tubes. They have them made to meet their exacting specifications. But the real story is their demise, then rise from the ashes like a phoenix. Read it here: Electro-Harmonix home page. They manfacture and sell quality audio and music amps and equipment.
Tube writing is reddish-orange with the same face screen printed on the tube as shown on the box. The date code is ww-yy and screened in black as is the country of origin.

Thanx to Damon Limeback for this fine box example. The two E-H 6L6GC's I have for sale were originally part of his collection.

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