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.
uses a Siemens 25W output transformer with a slight feedback from
the seperate feedback winding or (swichable) from the speaker
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
response is very nice (see picture) and the sonical qualities of
this amp are really outstanding.