Archive for April, 2009
Tubelab Simple SE Chassis Fitting
by Russ Knize on Apr.17, 2009, under Electron Tube Audio
All of the cutting and milling and drilling is finally done.
Here are all the various bits and pieces, made mostly from scraps, all put together:
More about the build here. Next step is paint….
Tubelab SE Breadboard with 300Bs
by Russ Knize on Apr.15, 2009, under Electron Tube Audio
With a custom power transformer from Edcor, I could finally try this amp with some borrowed 300Bs. This transformer’s primary is tapped so that it can be used with either 300Bs or 45s:
XPWR131 - 330-260-0-260-330 @ 175mA, 6.3 V CT @ 4A, 5V @ 3A
Voltages came in a bit high, even under load. The top row is the Tubelab SE in “45 mode”, with about 25mA per tube. Meters are reading: 660VAC winding, 520VAC winding, B+ at the filter cap. Bottom row is in “300B mode”, running Shuguang 300Bs (not mine) at about 28mA per tube. First two meters got swapped: 520VAC winding, 660VAC winding, B+.
With the 300Bs biased to 80mA, the 660VAC winding gets pulled down exactly to spec: 660VAC. B+ sags to around 370-375 VDC. Supposedly this is the ideal spot for the 300B. These tubes are Shuguang’s aptly-named “300BS”, which have mesh plates and globe-shaped glass. They have a weird blue glow on the glass, presumably from electrons flying through the gaps in the mesh.
