[Amps] How best to reduce filament voltage?

[Norman Hockler]

Ron,

Install a resistor on the primary side of the transformer.  Much 
lower current and the resistors will act as a
soft start for the filament to damp the inrush when you first turn on 
power.  Set the resistor value with the
tube on and warm  There are many sliding tap resistors available from 
the distributors or a fixed one will
work as well. Ohms law calculation to determine the value.

de Norm N8NH

At 08:16 AM 2/2/2007, w2cqm at juno.com wrote:
>I'm building a single tube 3-500  6m amplifier around an OEM SB1000
>transformer. The  Heath transformer is dual input 110/220VAC with HV,
>filament(5vct), and 12VDC secondaries on the  common primary. The
>original design of this transformer wound to accommodate the 3-500.
>The problem is that the filament secondary appears to be overly high
>and measures 6.5VAC no load and 6.09vac with the tube installed. Since
>there's an exponential loss of tube life with only minor filament
>overvoltage, I'm caught between a rock and a hard place. In this
>instance, the obvious answer is to install a dedicated filament
>transformer correctly designed for the application; however, that
>involves an additional (redundant) component. The question is whether
>it's somehow practical to reduce the filament voltage without getting
>involved with an odd ball low ohmage, high wattage resistor series
>installed on the secondary. Any comments would be appreciated. Ron
>W2CQM/3
>
>.
>
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