Just changed the stock BHK Preamp tubes to “select” tubes. When changing to “BHK select” tubes, Bascom mentions going from 4mA to 5mA bias (current), in addition to going from 12V to 6V. The bias selection is implemented using 2 stakes; connector is only on one stake (4mA). Connecting the 2 stakes with the connector changes the bias current from 4mA to 5mA. Current stakes are near the tube on the right. Below is a pic of the preamp and amp tube rolling process. In addition you can see how the Rx-9 dampener fits nicely. Below the preamp pic is the BHK250 amplifier pics. The Rx-9 dampener is a little wider than the SS-9 dampener and would have a tough time fitting; reason I went to the SS-9 dampener on the BHK250 Amplifier.
BHK Preamp:
BHK250 Amplifier
