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. |