Real McTube II Re-Visited

[Paul Marossy]

So I built the Real McTube II back in 2004 (http://www.dogstar.dantimax.dk/tubestuf/graphics/mctube2m.gif). Apparently I wasn't that impressed by it since it's been in my closet for the last ten years. For whatever reason, I decided to revisit the project because I remembered that it had some deficiencies due to the transformers I used (a pair of PCB mount RadioShack 12.6V 300mA), which yielded a low plate voltage of only about 113V. It just didn't sound that good. So this weekend I had an idea to just have the tubes filaments on their own transformer, same type as the aforementioned. That worked out really nice as now I'm getting about 152V after the filter caps, and the schematic calls for 140V.

Not shown in the video, but yesterday I figured out how to get the fan I had in there to work by changing that transformer I added to a 6V-0-6V 450mA instead of the 300mA. Knocked the fan down to about half speed with a 150 ohm 5W resistor (overkill I know, but I had it lying around waiting to be used in something) and a 25 ohm rheostat for fine adjustment.

So now I am in love with it. It works really well with my headphone setup. I have it on a clean setting with an ROG Condor in front of it, and it gets some really nice sounds. So finally after about 13 years I have realized the full potential on that little circuit and I learned a few things in the process although I still don't quite understand why the original transformers didn't get me the results I thought they should... I mean the tube filaments are 300mA at 6.3V and the plates are only about 10mA combined. Seems like there should be enough current but I guess something weird happens when you use them in that kind of configuration.

In any case, hopefully one of y'all will get something out of this.

[rutabaga bob]

Nice, Paul!  Glad to see the project finally have a useful life!

[Paul Marossy]

Nice, Paul!  Glad to see the project finally have a useful life!

Me too.