Driver Stage
In my
application the cathode voltage needs to be adjusted at about 30V
for close to ClassA operation. Now you could think that RL12s are
hard to drive, but a single tube driver stage works very fine.
Of course an
E88CC or an ECC83 would work fine, but these would be a sacrilege in
an RL12P35 amp. Classic driver tubes are: EF12, RL12P10 or ECF11.
For availability and socket reasons and good sonical experience
(Klangfilm KLV-204) I decided to use a triode connected EF12, which
works at a B+ of 200V with a 2.5kOhms cathode resistor.
Output Stage
My amp
uses a Siemens 25W output transformer with a slight feedback from
the seperate feedback winding or (swichable) from the speaker
winding.
The power output
is 5-7 watts sine wave almost undistorted - clipping starts at 11-12
watts, so there is a lot of headroom. I'd rate this amp at 10watts
output power.
The frequency
response is very nice (see picture) and the sonical qualities of
this amp are really outstanding. |