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RE: testing a 6L6GC in my EICO HF87?

If the tubes appear stable, I take the measurement at 10-15 minutes after power-on. However, many of the tubes I test are more than 30 years old. Even when the gettering looks good, they're sometimes gassy. In that case, I'll start them at a lower voltage to prevent thermal runaway, gradually raising the amp to full voltage (about +400V). This sometimes takes an hour or more, and the tubes have to be monitored all along the way. Once they're at full voltage, I let them cook for about another hour to hopefully burn off any remaining residual gas. Any tube that can't be raised to full voltage with an acceptable current draw, or that remains unstable after the full-voltage cook, goes into the trash.


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