Reply To: Backplate without mid-frequency adjustment

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John V

    Regarding SL_nirvana’s question about the values and power handling of the muti-tap choke, below is an explanation I received from Roger West back in 2018 as to why he resorted to an outboard choke to obtain the values he needed at the time:

    “Hi John,
    I’ll try to clarify the coil issue a bit more. Initially, we used a tapped coil that had 5, 10 and 20 mHy. I needed 1.5 mHy to complete my design, so it had to be an outboard coil. The outboard coil was attached to the 5 mHy coil, thus all values were boosted by 1.5mHy: 1.5, 6.5 , 11.5 and 21.5 mHy. At the time I felt that this slight change wouldn’t make any audible difference, and it didn’t. The small difference couldn’t be detected by the best of ears around here, but my addiction to my math analysis couldn’t be shaken, so I decided to change the values to what I initially wanted them to be. I changed the values of the coil to 1.5, 5 and 10 mHy and added the 8.2 mHy unit (mounted on a steel plate which increases the value to 10 mHy). No difference was to be heard, but I felt better. I found a source that could provide all four taps in one unit, which will eliminate the outboard coil. I hope I haven’t made this more confusing.
    Best, Roger ”

    Note that the schematic I posted the other day does show the values mentioned above.

    On another topic, regarding the brilliance control. Roger has mentioned that periodically its not a bad idea the rapidly rotate the control back and forth to remove any oxidation that may accumulate om the wiper over time causing a change in possible value.