Answer: To have an external heatsink to house the 21st Century Maida cascode mosfet. (I have a non neurochrome pcb) The board also has a Morgan Jones thingy onboard which I have read many say does the same as two resistors and a capacitor. O well. But it does raise the heater above cathode potential.
It's my first surface mount work..with normal soldering iron...so a little blobby...but it works.
It's my first surface mount work..with normal soldering iron...so a little blobby...but it works.
Attachments
For anode load Mills 12W, for cathode I use if power needed Mills 12W but if doesn't needs power I use Amtrans AMRG CARBON film or Tants if can afford, bypass cathode resistor BG or Elna Silmic II.
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I don't know if that will help further with suppressing harmonic noise in your build but as G3X is common cathode topology it certainly doesn't need it to avoid breeching heater to cathode max spec. That's useful enough in the cathode follower buffer version.
For sure it is not "needed" but apart from the cathode spec. I did some research...(bathroom type).
Allen Wright when asked why he said this:
"Nope. It is to 'lift' the heaters of the tubes above their cathodes - reverse biasing the inherent 'micro-tube' that exists between the heater and cathode itself and makes a surprising sonic improvent!"
https://www.diyaudio.com/community/thre ... ost-712662
http://www.valvewizard.co.uk/heater.html
"Heater Elevation
Elevation means referencing the heater supply to a DC voltage other than ground or zero volts. The heaters still operate at 6.3V or whatever, but this floats on top of the elevation voltage. Some valve stages such as cathode followers require the heater supply to be elevated to avoid exceeding the valve's Vhk(max) rating. But even when not explicitly needed, elevation can reduce hum in AC-heated circuits by reducing or saturating the leakage current between heater and cathode.* *See: Cooper, C. E. (1944). Valve Hum. Electronic Engineering, (July), pp72-5.
https://audioxpress.com/article/the-int ... cuum-tubes
"Some RCA data books recommend that you make the heater positive with respect to the cathode, ideally by 40 V or so, presumably to minimize noise. So as with everything in life, there are tradeoffs."
But we're dc heating. So might not even reduce noise...
Allen Wright when asked why he said this:
"Nope. It is to 'lift' the heaters of the tubes above their cathodes - reverse biasing the inherent 'micro-tube' that exists between the heater and cathode itself and makes a surprising sonic improvent!"
https://www.diyaudio.com/community/thre ... ost-712662
http://www.valvewizard.co.uk/heater.html
"Heater Elevation
Elevation means referencing the heater supply to a DC voltage other than ground or zero volts. The heaters still operate at 6.3V or whatever, but this floats on top of the elevation voltage. Some valve stages such as cathode followers require the heater supply to be elevated to avoid exceeding the valve's Vhk(max) rating. But even when not explicitly needed, elevation can reduce hum in AC-heated circuits by reducing or saturating the leakage current between heater and cathode.* *See: Cooper, C. E. (1944). Valve Hum. Electronic Engineering, (July), pp72-5.
https://audioxpress.com/article/the-int ... cuum-tubes
"Some RCA data books recommend that you make the heater positive with respect to the cathode, ideally by 40 V or so, presumably to minimize noise. So as with everything in life, there are tradeoffs."
But we're dc heating. So might not even reduce noise...
Roughly 8V across Rk and about 21mA through it. Even if bit more V & mA depending on tube tolerance, Rk will not dissipate more than 0.2W. So 1W is royal margin to never heat up enough. Guarded against extra noise and long time drifting.
@Bas Horneman
Yes I mentioned cathode follower and Vhk max too. Certainly not needed in G3X but if silent keep the lift. Maybe there's some side benefit or not.
In any case if there will be hum & buzz disengage the lift and ground the heater return.
Yes I mentioned cathode follower and Vhk max too. Certainly not needed in G3X but if silent keep the lift. Maybe there's some side benefit or not.
In any case if there will be hum & buzz disengage the lift and ground the heater return.
Not sure if exactly the same. B