I am about to start building my first DHT amp - a 45 parafeed headphone amp, with the output being cascode CCS loaded (IXYS depletion-mode MOSFETs) and auto-biased.
I am using Rod Coleman's filament regulators. Re-reading the manual, I realized I had overlooked a design consideration - I do not have a delay / soft start mechanism for the B+.
How concerned should I be about applying bias when the filaments are partially warmed, along with cathode stripping? Given this is a headphone amp, the 45 bias is not aggressive, around 200V at 32mA. My understanding this is more of a concern with transmitting tubes with kV-level anode voltages.
Space, power supply, and layout considerations would make adding a soft-start PCB quite the pain. I am inclined to move forward without it, but would love to hear some opinions, seems cathode stripping is something of a controversial topic 🙂 thank you.
I am using Rod Coleman's filament regulators. Re-reading the manual, I realized I had overlooked a design consideration - I do not have a delay / soft start mechanism for the B+.
How concerned should I be about applying bias when the filaments are partially warmed, along with cathode stripping? Given this is a headphone amp, the 45 bias is not aggressive, around 200V at 32mA. My understanding this is more of a concern with transmitting tubes with kV-level anode voltages.
Space, power supply, and layout considerations would make adding a soft-start PCB quite the pain. I am inclined to move forward without it, but would love to hear some opinions, seems cathode stripping is something of a controversial topic 🙂 thank you.
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Unless that the amp is DC coupled, the fact of powering on simultaneously heaters and bias is the normal condition. In the tube era, a simple B&W TV used about 20 tubes and SS rectification. The set was working about 12 hours/day, and it was in use about 30 years or more, no kind of soft start nor heater/Ebb delay was used. Don't worry and use it as is.
Osvaldo - thanks for addressing my concern, very pleased no changes will need to be made - be well!
To be clear, you can do a delay, but you don't need a delay. Do it at your own taste or what your instinct say to yourself.