300B-mesh, NF2 Amplifier.

Last Update:

AD1, NF2 Amplifier. K. Anzai, JAPAN. Also used by Jean Hiraga.

I was not able to find much about Mr. K. Anzai, Japan, other than that he was a circuit designer from Japan. If someone can find some more, please let me know, so I can place it here. Some people report this schematic was also rebuild by Jean Hiraga.

Also the schematic shows great resemblance with the Yamamoto AD1 amplifier, first generation. The resemblance is very large, probably there are some connections.

Interesting, Lundahl has the right transformers in the program, we re-build the AD1 at Emission Labs, and I have a small stock of NOS Telefunken NF2, some in sealed boxes even. NF2 has a top cap, but this is for the grid1. So there is no DC voltage on the top cap. It is advised you use an coaxial cable to connect to the grid 1, and ground the cable shielding. Yamamoto has very nice Teflon plate caps. The NF2 is a glass tube, but it has conductive (bronze) painting from the outside. It has the same socket as AD1, and is from the same period. So all on all this is a very nice combination.

I have not tested the schematic myself, but a few DIY build the first version successfully. This is here, is the second version, Rev.B. Some small changes were made. The Yamamoto meter was removed, because it is obsolete. The volume control was moved to the second stage. The power supply capacitors of the second stage are larger. This amplifier should would work problem free, and is easy to build, because lots of adjustments can be made easily.

The Filament voltage of the AD1 must be adjusted to 4V, the NF1 12.6V. Note, the EML AD1 draws a more filament current than Telefunken, and some other kind of tubes exist too, which can be used instead of AD1. So use the variable resistors in the filament circuit to get exactly 4V. The transformer has enough AC voltage to use stabilizer ICs, or other filament electronics, like filament chokes from Lundahl. Anyway, you can do that as you whish. Perhaps try it with AC heating first, as shown here with very little effort, only a variable resistor is used. If not totally hum free, add DC heating. (This may be needed above 100dB speakers)

About NF2 tube.

Little is known about this tube actually, but it was intended as a very high quality pentode for secret radio receivers, in WW2. I have a book about this. NF2 was found in the so called "EBI-1 building block", which was the part of the first-ever made electronic guidance systems for airplanes, by the Germans in WW2. This application required extremely stabile and noise free tubes. Because of it's side socket and grid cap, DIY say they "do not like" this. That is good, because now 80 years later, you can find these remarkable tubes NOS, or used in excellent condition.

A special article about the NF2 is here.

Amplifier Specifications:

Frequency range at full power 5...80KHz @ 3dB (with Lundahl transformer)