Very very very low voltage tube preamp

[PRR]

Albert van Dalen has demonstrated a tube preamp working at 3.3V, both heater and plate.
https://www.avdweb.nl/tech-tips/tips-2/3-3v-vacuum-tube

I'm avoiding saying the word "amplifier" because as I figure it, the power gain is less than unity. It weakens signal!

It claims a voltage gain of 3.5. However the signal grid must be run positive to get plate current to flow. This and the way he get the positive bias makes the input impedance near 600 Ohms. The plate resistor is 10k. So the R-C-coupled load must be greater than 10k, but assume it could get voltage gain of 3.5 between a 600r source and a 10k load. 3.5X voltage in 16X the impedance is 0.22 current. 3.5*0.22 is power gain of 0.76. As an amplifier it is worse than useless.

Which is what we expect interpolating tube power gain down from 300V, 100V, 30V toward 3V supply. Voltage gain falls slowly (to a point) but current falls faster than voltage, so power gain falls off bad.

Note also that grid current is twice plate current.

[willienillie]

I always heard lowering the voltage was the secret to the Van Dalen sound.



(sorry.)

[Steben]

It is, of course, kind of an experiment.
We don't need 3.3V to reach a voltage that meets safety margins or battery limits.
Just think of 12U7 for example. A (twin) triode designed for 12 volts.

[amptramp]

This site:

http://www.sophtamps.ca/www.sophtamps.ca/mambo/index862b.html?option=com_content&task=view&id=25&Itemid=37

has a number of 12 volt tube amps that have high input impedance and reasonable output.  There were a number of 12 volt tubes created for car radios that had all tubes except for a germanium power transistor for the output.  This eliminated the vibrator and power transformer that had been used before that.

[idiot savant]

This site:

http://www.sophtamps.ca/www.sophtamps.ca/mambo/index862b.html?option=com_content&task=view&id=25&Itemid=37

has a number of 12 volt tube amps that have high input impedance and reasonable output.  There were a number of 12 volt tubes created for car radios that had all tubes except for a germanium power transistor for the output.  This eliminated the vibrator and power transformer that had been used before that.

I've had some success using these low voltage pentodes in a few projects.

Here's a little FX loop gate thingy I made a few years ago:




More info on low volt tubes:

http://www.junkbox.com/electronics/lowvoltagetubes.shtml

[j_flanders]

I always heard lowering the voltage was the secret to the Van Dalen sound.

LOL! Best one I heard in a long time.

[GFR]

Any realtion to wat's inside the Vox "cooltron" pedals?

https://www.diystompboxes.com/smfforum/index.php?topic=37642

[amptramp]

Thanks idiot savant, I hadn't seen that site you linked before.  There is a lot of good tube data there and information on how to design for low voltages.

[Nasse]

I used to have vintage 6 volts car with tube radio (Blaupunkt). Quite short heating, radio was making sound after passing two electric poles.

[merlinb]

Just gonna leave my own low voltage article here for reference:
http://valvewizard.co.uk/Triodes_at_low_voltages_Blencowe.pdf