RCA 12BH7 NOS in box matched sections

doctorcilantro

Single gray plate halo getter; asking $19 shipped.

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Testing Protocol (Amplitrex AT1000)

Each tube's electrical properties are analyzed for heater-to-cathode leakage, shorts, grid leakage (gas test), plate current (emission), and transconductance is measured. Results are noted on a label for each box. Matching is within 10% plate current and 5% transconductance unless otherwise noted.

Interpreting Amplitrex Results Correctly

For preamp tubes, we reject those with greater than .1uA of grid leakage; for power tubes with reject those with greater than 2.5uA of grid leakage. This is more important in a power tube, due to the possibility of creating "runaway" conditions in circuit. We have tested preamp tubes (5687) with 52uA of grid leakage (on both sections = gas) in a driver position with no apparent problem other than a reduction in gain, and one of these tubes actually recovered from it's gassy state after a 2-hour circuit burn-in to read .9uA of grid leakage. Many unused NOS tubes can recover because they have never had their getter "activated". However, excessive grid leakage on only one section indicates a structural defect due to contamination or wear, thus recovery is impossible. We take extra care to utilize the Amplitrex results correctly to weed out problematic tubes based on the aforementioned information. Protect your circuits: there are approximately 120 Amplitrex units in the field, and not are all are being used as directed.