Stiletto Variable Bias Mod

[chunkitup]

I am adding a variable bias trimmer to my MB stiletto and I was wondering if I need to worry about switching from silicon rect and tube rect. The plate voltage would change.

[defaced]

Check the schematic to see if there is a resistor in the bias circuit that is switched with the rectifier, I seem to remember there being one in the Rectos, but I honestly don't clearly remember. If not, then experiment and see what happens to the power tube dissipation in SS and tube recto modes. If it stays in spec, I wouldn't worry about it.

[chunkitup]

I took the chassis back out. I drew the bias section out and it had two resistors in parallel that I correctly guessed were for a 7.9k resistance which gave a -39v. I never checked to see if perhaps one of the resistors were switched out when in tube rect mode but it stays in parallel. I am good to go.
Thanks Mike

[Pedro Vecino]

Bias circuit is common for both modes (diodes / tube rectifiers). You must select bold mode and diodes to adjust. If you want automatically accommodate the bias adjustment for the tube rectifiers should be automated with another circuit.
In Trident models also must take into account the tubes selection (one pair / three pairs) and find a weighted average. If you make a good adjust for the sextet, selecting only a pair, this will rise too.
Regards