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RE: Measure heater voltage---Important!!

There's another potential problem with the 40M design regarding the 6SL7. At least in the version I had, the 6SL7 heaters were referenced to ground which put the heater-cathode voltage over the max rating due to the split load inverter. As I recall, the H-K was around 110 or 130v. I burned up a couple NOS 6SL7 tubes before figuring out that issue. Fortunately the tubes I liked best in that spot (Brimar CV1985) were not bothered by the high H-K voltage. Had I kept the amps, I would have added a divider network off the B+ with roughly a 65vdc tap and connected it to one leg of the heater supply, which would have allowed more flexibility with other 6SL7 types.


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  Kimber Kable  


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