One B+ for the both driver and output tube if they are identical?

[vhrynchuk]

Is there any disadvantage to feed a driver and an output tube from the same B+ PSU if the driver and the output tubes are the same DHT connected through an interstage transformer and the PSU has enough current in reserve?

Thank you.

[ray_moth]

Probably no disadvantage, even if you don't decouple the HT between the stages. However, with more then two stages there is a risk of positive feedback between the 1st and 3rd stages, which can lead to LF instability (motorboating). It's normal practice to decouple the HT for every stage.

[zobsky]

kinda unrelated, but I'm assuming you an RC decoupling scheme is typically used. What kind of R and C values should one aim for (assuming there is no need to burn off voltage)?

[ray_moth]

I seem to remember reading that capacitance in uF x resistance in ohms/1,000,000 should be 0.1 or greater, for good decoupling.

So, from this rule of thumb, if you want a small voltage drop and use e.g. a 470 ohms resistor, the minimum capacitance you need = 1,000,000x 0.1/470 = approx. 220uF.

[vhrynchuk]

Thank you for the responses!

[zobsky]

thanks from me too