[Homeroast] Roasters

raymanowen at gmail.com raymanowen at gmail.com
Thu May 20 03:22:20 CDT 2010


"...you may have to add a Variac to your roasting equipment"

By that reasoning, electric ranges, ovens, toasters and hair dryers should
have been extinct for the past century. The Variac is an auto transformer-
the primary and secondary are incorporated in a single, tapped (toroidal)
winding.

The Tetrode vacuum tube is a particularly non-linear electric valve. You put
Liberace on the grid, but you don't exactly get Lee on the plate/ primary of
the output transformer. Absent some ringing, what goes on the primary of a
transformer is the exact wave shape you will get on the secondary and
speaker voice coil/ cone excursion/ sound pressure waves you hear.

To harness the efficient but non-linear tetrode (or beam power tube) for
audio use, the ultra linear output transformer provides negative feedback
for the screen grid to make the tetrode's transconductance more linear.

The plate current is a high-fidelity (Hi-Fi) image of the control grid's
potential waveform. The plate current goes through the transformer primary.
The secondary goes to the speaker voice coil.

Variacs, and most other transformers are not electronic mufflers. Put spikes
and brownouts in, and that's exactly what you will get out unless you stand
there and keep varying your Variac.

Cheers, Mabuhay -RayO, aka Opa!

If it feels good, twist your Variac...

Got Grinder?


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