26-04-2018, 04:09 PM
I'm not so sure about that. Recalling the vast improvement to emissions from flat CRTs when fed by a 20% boost transformer but the relatively short time that the rejuvenated tube usually lasted, I'd err on the side of caution, particularly if replacement valves are difficult/impossible to find or only available at highly inflated prices.
Don't forget the origin of the 6.3 volt heater goes back to the era of the lead acid battery which was not the generally accepted 2V per cell but actually 2.1V per cell. Early valves had 2V filaments and were powered by a single cell and followed by 4V valves and two cells. By the time the heater voltage had gone up to the 3-cell level, manufacturers decided it was time to take into account all those 0.1V increases and made them 6.3V.
6.3V is a 5% increase on 6V; 6.7V is a 6.3% increase on 6.3V. It might be wise to add a suitable series resistor to either the transformer primary or secondary, whichever you have a suitable resistor for. If the secondary is centre tapped, the primary would be easier to deal with.
I find it strange that a piece of test equipment which might be left switched for long periods so as to be instantly available for use, did not have primary taps on the mains input.
Don't forget the origin of the 6.3 volt heater goes back to the era of the lead acid battery which was not the generally accepted 2V per cell but actually 2.1V per cell. Early valves had 2V filaments and were powered by a single cell and followed by 4V valves and two cells. By the time the heater voltage had gone up to the 3-cell level, manufacturers decided it was time to take into account all those 0.1V increases and made them 6.3V.
6.3V is a 5% increase on 6V; 6.7V is a 6.3% increase on 6.3V. It might be wise to add a suitable series resistor to either the transformer primary or secondary, whichever you have a suitable resistor for. If the secondary is centre tapped, the primary would be easier to deal with.
I find it strange that a piece of test equipment which might be left switched for long periods so as to be instantly available for use, did not have primary taps on the mains input.
