With all due respect...the $35 CV4024 we have would be for the top grade and will have the tightest triode balance, lowest noise and hum, and tested for the highest gain line or phono stages. Each tubes is measured in circuit, and listened to with headphones.
So the princely sum of $35 ain't much. Certainly not a profit center here at Upscale Audio.
But they are the best made 12AT7 ever so even if you do buy off E-bay or "The 99 Cent Store" you may be OK.
Cheers....
Kevin Deal