Low supply or voltage doubler for 12AX7 ?

[brett]

Hi.  I'm building a 12AX7 preamp using a 220V:110V power transformer for the B+.
Full rectifier and some RC filtering will give me about 150 V DC.
A "voltage doubler" rectifier (schematic) and some filtering will give me about 300 V.
Because I've never run a 12AX7 on a supply as low as 150 VDC, I'm reluctant to try it.
300V gets me a classic supply, but requires hefty capacitors for smoothing and potentially some ripple at the output (around 1V for 2 x 22uF capacitors, prior to filtering).
Thanks for any suggestions.

[antonis]

Because I've never run a 12AX7 on a supply as low as 150 VDC, I'm reluctant to try it

https://www.diystompboxes.com/smfforum/index.php?topic=19817.0

[digi2t]

https://www.diystompboxes.com/smfforum/index.php?topic=129257.0

[amptramp]

The maximum rated operating voltage for a 12AX7 is 300 volts but most 12AX7 circuits operate from lower voltage.  I have a receiver where the phono preamp stages are 12AX7's operated from a 135 VDC supply.  The actual plate voltages for the two stages in this preamp are 65 volts and 85 volts for the first and second stages respectively.  The 12AX7 stereo multiplex amps operate from the same 135 VDC supply and the plate voltage is 97 VDC.  The same receiver has a 12AX7 tone control amp stage that operates from a 196 VDC supply and the plate runs at 105 volts.  The power amp uses a 12AX7 for first amp stage and inverter and the first amp stage runs from a 263 VDC supply and the plate runs at 93 volts.  The inverter runs from the same 263 volt supply and the plates is at 165 volts and the cathode is at 95 volts.  In all cases, the plate resistor drops the voltage from the supply.

The 12AX7 dual triode has the same characteristics as the 12AV6 triode dual diode tube used in AC-DC radios where the supply voltage is 120 VAC and the tube is operated with a supply voltage of about 100 volts and a plate voltage of about 82 volts.  There is supposedly better linearity (which translates into lower harmonic distortion) at higher voltages.  The 150 VDC supply is perfectly adequate.  The 300 VDC supply is approaching the limit for the tube and will result in shorter tube life but will allow for more voltage output if you need it.

[PRR]

The "upper end of 12AX7 supply voltage" is about 470V, because we normally bias at 70% of supply, and you can run 330V in-spec as long as you "know" it won't be over that.

However McIntosh ran over 400V plate-cathode on several widely used models for decades.

The *lower* limit is, by an old superstition, about 100, or 1V * Mu. There's more-or-less 1V of poorly controlled "contact potential" effects around the grid-cathode, so if the plate supply voltage is not Mu higher the bias may not be stable.

As Ron's extensive enumeration shows: voltages which look teeny to guitar-amp eyes were absolutely standard in hi-fi (where levels are more knowable than in g-amps).

[brett]

Thank you so much to everyone.  I'm feeling better about a 240 V AC supply through a 220:110 transformer and bridge rectifier. 
That gives me 165-170 VDC before filtering.  With lower than usual R (1k) and higher than usual C (220uF), I'll hopfully have 160V for B+.
The 12AX7 triodes are in series (wirh a gain control between), so I'll have more gain than I can use, even with a wasteful tone section and volume control.  The power amp tube is one of those $3 Chinese 6J1 (max output 0.4W).
Thanks again.