Today my father and I went to an undisclosed location in the western part of the state, to buy this rheostat:
The rheostat is rated at 10 Ohms and 25 watts. In circuit this provided us with a current range across our filament from 0.5 to 1.4 Amperes. This is great since 1.6 amperes is the max current recommendation in the Sylvania datasheet.
Using a non-contact pyrometer we tested the rheostat knob for heating...
10:32 83 degrees (Room temperature for our third floor apartment with radiator heat!)
10:35 87 degrees.
This is fine, as Sylvania only recommends using the tube in five minute bursts.
While the rheostat is lossy in terms of power it has the benefit of adding only random noise, whereas a transistor under (op-amp) control could add noise from its feedback control system that could pollute our noise with causal signals.
I also installed a shielded tube socket without screw terminals for better signal quality. An ebay order came with tubes for a possible thermionic noise pre amp. They were previously used by silent key Billy G. Orock, Sr. (W7GSY) and I hope he approves of their new home.
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