Need an ok for a simple tube amp design. Will this work?

[Thecomedian]

9v DC supply.
Want 4.5v on anode.

Will this function?

[psychedelicfish]

33p for coupling caps What is this for? Is it a preamp? Is it a poweramp? What tube are you thinking of using?

[Thecomedian]

I took those values from a test circuit for the tube from a data sheet place. I know the impedance of tubes is pretty high, so I thought maybe the capacitance didn't need to be too high, which is why the sheet used 33p.

Should I make them bigger?

it's a preamp pencil tube that uses 0.011mA 6.3v heater.

http://www.russiantubes.com/prop.php?t=12&p=7

[psychedelicfish]

The circuitry looks OK, I'd definitely increase the values of the coupling caps though. It may not work at that low of a voltage though, I'd try find some way of getting a higher voltage, say 24V or so.

[Thecomedian]

Okay, thanks.

This one has proven to work at 9v http://www.diystompboxes.com/smfforum/index.php?topic=63479.0 so I thought this one would work even better because it has a very low current drain in comparison, which would free a pedal from needing an adapter supply.

I'll try it and post results on whether it does anything 'useful'.

On a side note, would it be possible to use 2 9v and then double that up to 24v, or should a wallwart be used if you want to go that high?

[Lurco]

I took those values from a test circuit for the tube from a data sheet place. I know the impedance of tubes is pretty high, so I thought maybe the capacitance didn't need to be too high, which is why the sheet used 33p.

Should I make them bigger?

it's a preamp pencil tube that uses 0.011mA 6.3v heater.

http://www.russiantubes.com/prop.php?t=12&p=7

I highly doubt that! 11µA?

[Thecomedian]

Yeah, tube technology kept progressing in the shadows of transistors, like a growing mold under the fridge that hasn't been cleaned out yet. Most tubes follow a rule of high voltage, low current, anyway. these things are tiny, think about the same size and shape as 2/3 of your pinky finger, just slightly even less diameter

[PRR]

> I highly doubt that! 11µA?

"mA" is milliamps. 11mA is 0.011 Amps.

Yes, this is astonishingly tiny for a 1.2V tube. I expressed doubt in another thread he started, but it's true. (Actual test on one sample at 1.204V gave 12mA.

microAmps would indeed be even more unlikely.

These tubes were used in USSR aircraft radios in the period when transistors were new. They can have a power efficiency (including heater) better than the average Germanium transistor. However this is at nominal 60V on Plate. Performance at 9V or even 24V will be pathetic.

[PRR]

You need to learn Basics. Like power consumption in a resistor. And appropriate capacitors for audio amplifiers.

33pFd must come from the original use: _high_ frequency _radio_. Makes sense for 50MHz fighter-aircraft radio. NOT audio.

Steal audio cap values from *audio* amplifiers. Input cap can be 0.01uFd. Output cap can be 0.1uFd. G2 bypass maybe should be 0.5uFd; however at this _LOW voltage I suspect you want to tie G2 to your most positive voltage (perhaps through 10K to protect against shorts).

[Lurco]

> I highly doubt that! 11µA?

"mA" is milliamps. 11mA is 0.011 Amps.

Yes, this is astonishingly tiny for a 1.2V tube. I expressed doubt in another thread he started, but it's true. (Actual test on one sample at 1.204V gave 12mA.

microAmps would indeed be even more unlikely.

These tubes were used in USSR aircraft radios in the period when transistors were new. They can have a power efficiency (including heater) better than the average Germanium transistor. However this is at nominal 60V on Plate. Performance at 9V or even 24V will be pathetic.

Yes. Nevertheless The Comedian wrote: "it's a preamp pencil tube that uses 0.011mA 6.3v heater.", which made me wonder!

[Thecomedian]

You need to learn Basics. Like power consumption in a resistor. And appropriate capacitors for audio amplifiers.

33pFd must come from the original use: _high_ frequency _radio_. Makes sense for 50MHz fighter-aircraft radio. NOT audio.

Steal audio cap values from *audio* amplifiers. Input cap can be 0.01uFd. Output cap can be 0.1uFd. G2 bypass maybe should be 0.5uFd; however at this _LOW voltage I suspect you want to tie G2 to your most positive voltage (perhaps through 10K to protect against shorts).

Thanks. Can I ask about the 47k Anode R and R/C on cathode? I just took cathode straight to ground as I saw in other schematics, but is it better to have R/C combos? Is it for feedback bias as per transistor?

I forgot about the cutoff frequency business of caps cause I just wasn't thinking about it.

G2 is "nominal" 45v, G1 is "nominal" 0v, and Anode is "nominal" 60v.

so G2 is a 3/4th ratio to Anode, which seemed like a good theory to start with, which is where the 90k resist anode and other resistances came from. also, G2 needs 90uA to 100uA current. I did this cause I read that screens should be at some fraction of the anode voltage, and the fraction the data sheet gave was 3/4th.

I assume you'd want series resistances in the 10k-100k range to limit power consumption for resistors?

http://www.allaboutcircuits.com/vol_3/chpt_13/4.html

I took the screen voltage division/capacitor setup from here.

[PRR]

> G2 is a 3/4th ratio to Anode, which seemed like a good theory to start with

Yes, but you are using VERY low voltage, 9V or 18V?

G2 voltage sets the maximum current in the tube. Over 100V we can usually get plenty of current. At 60Vp in thrifty radio work, apparently 45V was fine. But down at 9V the current gets VERY small (tube current goes down _faster_ than voltage). I suspect you want all the G2 voltage you have.

[PRR]

That AllAboutCircuits plan is very simplified.

You "usually" want Cathode Bias. The unbiased form you used can "work", but unpredictably, and distorts easily. (However this may be what you want? Try both ways.)

If you are looking for the classic Fender/Marshall "tube sound", you may not get it. The construction of these "rod grid" tubes is *totally* different from the wire-grid construction used in all other tubes, and particularly how the 12AX7 is constructed. Joe Sousa has plotted these rod-grid tubes. In many ways they are more like FETs or even BJTs than classic vacuum tubes.

[Thecomedian]

Yeah, I noted their marked difference in internal design. Well, if it doesn't work out, I'm sure they may be a decent higher voltage pre-amp.