inspired by this article on the net, http://www.veiset.net/6LU8/index.html
i decided to build myself one, i have ordered about 700 pcs of these $1 tubes from Roy and Dale Rogalski of http://www.vacuumtubes.net/
now it's time to put them to good use:
the 6LU8 is like a 6V6 and 1/2 of 12AT7 placed in s single 12 pin compactron envelope, i wanted to use the 21LR8 at first but then the novar sockets had issues, they were loose, i found out that they were intended for tubes like the PL504 which had thicker pins.....oh well.....here is the link for the 6LU8: http://frank.pocnet.net/sheets/123/6/6LU8.pdf
so i designed all the irons needed, the power transformers, filter choke and output transformers, the 2 output transformers used Edrel's RM20 cores which like his more expensive Z11's had the same 0.35mm thikness, Deeco Irons were then used for the power transformers and filter choke, deeco iron has a thickness of 0.5mm....
pics of the irons and some parts:
the power supply used the 3DG4 tube,http://frank.pocnet.net/sheets/093/3/3DG4.pdf
it is likewise a hybrid rectifier using solid-state bridge, a toggle selector switch is used to select ss only rectification if desired.....the advntage of a hybrid is that being a full bridge rectifier transformer heating is way much lower than if staright full-wave is used using tube rectifier only......design and construction of the power transformer then becomes easier and cheaper....
i used another set of speakers to test whether the polarity of the output transformer was correct, there is a 50-50 chance you will get it, but upon power up motorboating happened so i had to power down and reverse the plate lead connections to the right one.....after that, the amps was dead quiet, no hum, no hiss no noise.....i tested the amp and found out that the sensitivity was quite low, so i hooked up the 7N7 preamp to get a more decent volume.....later on i found out that i connected 470ohms feedback resistor instead of 4.7k so gain was really low....