Amps found in the bigger radio consoles and also part of a module line for DIY systems.

  I think this is one of my favourite EL84 PP amps. Its design is very simple and it sounds very well in original condition. It uses fixed bias and low feedback. Compared to many other EL84 amps (as Leak ST20) I sonically prefer this one (the Dyna 35 is very nice, too).

History and Changes:

Stereo-Endstufen-Chassis:

  Ultra rare earliest version of the EL84 PP amp (shown left). Some significant changes followed: Only this version uses a choke in the power supply and has trim pots to adjust the driver tubes !!!!

NF2:

  The most common amp of these. Usually having a cage as dangerous voltages on upper side of chassis touchable.

NF20: 

  The NF20 is similar to the NF2 but provides DIN jacks for speaker connection. 

Grundig NF10 and NF2 (later version)

  The earliest "NF2" (is was not its name yet) was designed to work without cage. So the lines voltage connector and the fuse are mounted inside / from the back side and not dangerously touchable (see right) from above as in the later models.   These later NF2 / NF20 amps used octal sockets for the preamp and speaker connection. The first models used rare 9-pin connectors instead (see below).

Take care . . .

1.   The later amps use little coils in the feedback loop. I have seen some of these burnt in some units. Check this if your amp does not work properly.

2. The power transformer is something delicate. I recommand to use it on the higher rated taps (240V for 220V use and 117 for 110V use)

Grundig NF20 (slightly modified with RCA jacks, filter cap and polished chassis)