Hi,

I aim for designing a tube amp but first I wanted to start with your low-Voltage Tube Circuit. Is it able to overdrive fast? Because I would like to use it with my guitar and maybe mod it for better guitar sound. 

Best

Dave

Hi

Nice to meet you after viewing your profile i am Jacinda, from (jakarta) indonesia,

i have a project discussion with you please email me on: (jacinda.seiler@yahoo.com)

I have several questions about the project:

1. Would it be really bad if I used a semiconductor diode or a different tube instead of the PY88?

2. Are there any alternatives to the ECL82? Can't find it. Could it be replaced by 2 tubes with similar ratings - a triode and a pentode?

Thanks in advance!

Simas, LY3EU

Also what is the ratio of the output ttransformer?

what are specs of power supply transformer that you used?

yes, i like tubes a lot. i have some JAN8930 transmitter tetrodes i've been meaning to build out. slip cast porcelain sockets, whisper fan forced air chassis with glass chimneys, hand wound toroidal transformers...mmm...i need some me time in the corner!!!

keep at it - i'll live vicariously through you for now.

What kind of output transformer did you use?

Well, I like the simplicity, but the design has a few flaws.

1, PY88 isn't the best tube for this application, but nevermind. If its filament voltage is 6,V, is is very underpowered - PY88 (as other tubes starting with P) is intended into 0,3A serial connection, this particular asking about 30V at filament. You can derive this voltage from 40V secondary, with series resistor. When you underpower tube, it's cathode is colder, so asking for nominal current means much faster cathode wear-out.
Underpowering the filament is always harmful for power vacuum tubes.

2, 3300uF bucket. It is not needed to have such as huge cap, actually - huge capacitance is harmful for the diode. This is not like semiconductor circuits, where "the bigger the better" rule applies to smoothing capacitors. Big capacitance means bigger current spikes (we all know how rectifier works, do we? - http://www.circuitstoday.com/wp-content/uploads/2009/08/half_wave_rectifier_with_capacitor_filter.jpg ). Rectifying tubes usually had specified maximal capacitance of first smoothing capacitor http://www.drtube.com/datasheets/ez80-philips1953.pdf
Combined with point 1, you are pushing the rectifying tube quite hard.

3, No grid bias and low anode voltage means low output power and higher distortion. Maybe it could be somehow usable as instrument amplifier. The high voltage usually found in tube circuits is there for a reason other than distracting the beginners ;-)
ECL82 in SE configuration can output a few watts, with proper circuit/voltages. It doesn't seem like much, but with sensistive guitar speaker you can do a lot of buzz with it.

4, R2 could be higher. 100k means you are loading the preamplifier too much, even more decreasing the gain of poor underpowered tube. 470K should be OK, giving slightly more gain as well as wider frequency response (because of C2).

Apart from that, nice amplifier. Good luck with further vacuum tube designs, it is rewarding and interesting journey.

I made a mistake in the description, the PY88 does get the 30V just the way you said. I have corrected this.
For the other points, thank you very much for your advice, I'll take a look at it :)

This is one of the best tube amp projects I've ever seen. Really, everything is right there, it's simple, and you can just *look* at the schematic and figure out the block diagram.

Do you have a video/audio of this amp in action? How's the gain if you push it hard?

I havent made no video because I lost my Youtube password :P But well, with the potentiometer at the input you can adjust the gain, so at full loudness its very distorted, but if you go down, you can get adequate room volume with little distortion (depends of course also of your speaker).