Here is an explanation for the paper labels from the Tubemonger’s website, except your labels were printed, not handwritten. I would remove them if you can:
The input tube will have more impact on the sound, but both can have an effect.
It appears that the 6414 is a variant of the CV4033/12AT7 according to the Brent Jessee website, but it’s always best to check with the manufacturer before substituting. They may also recommend brands of tubes to try. Most manufacturers are happy to answer these types of questions.
*Each tube came with two factory stickers (click Larger Photo). A hand written individual serial number, and a handwritten number PM25525-1. Tube boxes also have a sticker with printed number PM25525-1. Tubes were factory tested and serialized for some qualification (PM25525-1), except we don’t have specific details of the qualification.
The input tube will have more impact on the sound, but both can have an effect.
It appears that the 6414 is a variant of the CV4033/12AT7 according to the Brent Jessee website, but it’s always best to check with the manufacturer before substituting. They may also recommend brands of tubes to try. Most manufacturers are happy to answer these types of questions.
6414:An industrial, computer rated dual triode,virtually the same specs as the E180CC or 7062 listed above. Unlike the E180CC, this tube was made in the USA. It is a more rugged build, with the Raytheon blackplate type sporting triple mica and military ratings. This tube is also like a 12AV7 and will work wonders in any 12AT7 spot, and may be just the ticket if you want to boost the gain of a 12AU7 circuit. The 6414 is getting very hard to find, but with a 10,000 hour heater rating you may never need a replacement. Discussion groups rate this type very highly for use in headphone amps. Stands about 1/2 inch taller than the standard 12AT7.6829: