Ok, that makes sense now. This is probably a great reason to connect the safety diodes to the “free” pins on the rectifier socket and use them as a standoff. This is where I’ll tap for a proper bias feed. Hopefully I’ll post with a reply of success tomorrow morning.martin manning wrote: ↑Sat Jun 07, 2025 12:46 am Looks like your HV input lead is coming from the DC side of a safety silicon diode. It needs to be connected directly to the HV AC.
Verify My Mini Bias Board for a 6G3
Moderators: pompeiisneaks, Colossal
Re: Verify My Mini Bias Board for a 6G3
Greg
Re: Verify My Mini Bias Board for a 6G3
This morning, I made the changes that were necessary to obtain negative voltage for the bias. Happy to say that all is working perfect. Thank you all for helping me out.
Dialed the amp with a warm bias of 70%, and it sounds really good. Later, I'll play around with the bias more when I have a better opportunity to crank it up for an extended time. I started with a 150K for the bias range resistor, but I couldn't get the current below 44 mA's which is way too hot. A 100K allowed me to set the bias at 23 mA's for 70% dissipation (430v at the plates) with enough travel left to get down to at least 50%.
A couple more gratuitous pics...:
Dialed the amp with a warm bias of 70%, and it sounds really good. Later, I'll play around with the bias more when I have a better opportunity to crank it up for an extended time. I started with a 150K for the bias range resistor, but I couldn't get the current below 44 mA's which is way too hot. A 100K allowed me to set the bias at 23 mA's for 70% dissipation (430v at the plates) with enough travel left to get down to at least 50%.
A couple more gratuitous pics...:
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Greg