This is not an all-tube amp. There are a lot of transistors alongside two 12AX7 in the preamp stage. It is indeed they who bring the grain saturation particular JCM900. It is also thanks to them we can obtain large saturation even at low volumes unlike JCM800 example. The combination of transistors and lights returned to some sort to have a distortion pedal included with the amp head.

For the power (which is all-tube):
A 12AX7 phase inverter followed by a push-pull four EL34 (the 5881 U.S. model).

UTILIZATION

The tone stack is not what I've seen better. Do not hesitate to set equalizer to max or zero. I see so many guitarists who do not dare turn the knobs and put everything at noon.

SOUNDS

The clean sound is not up to the race condition JCM900 but was not designed for that. This is an amp for lovers of Rock and Hard Rock distortion.

OVERALL OPINION

I have since 1999. Buy € 530 at the time with the baffle 1960A.
By dint of perseverance and testing of any kind I finished not find a config that pleases me.
Fender Jaguar Boss SD1 + modified + clear + channel JCM900 Cabinet Mesa Boogie 1x12 Thiele.
I never use the boost channel because I find it lacks dynamics and spring mixes poorly. In short, the boost channel did a lot of noise but nothing is heard.

Added 10/04/2010:
I change all the preamp section for it to be 100% lamp except the reverb which remains transistor. It remains only a single channel like a JCM800 but with two gain settings and two input (high & low). Here was a lot of work but I am happy with the result for only 20 € component by taking the best quality. As against this no longer really a JCM900.
I made a post about the transformation for those interested:
https://www.projetg5.com/modules.php?name=Forums&file=viewtopic&p=54549 # 54549