Some Preamp, ...need Schmeatic.

[lukas]

I have this preamplifier, i check transformers, works good, tubes check too, but i need schematics...

 

[rock soderstrom]

This is an interesting mic pre amp, obviously from Germany (or Austria). We see two gain stages with EF12k with large input and output transformers and a gain pot in between. a gain pot before the first gain stage.

The power supply is tube rectified with an EZ11, the amp is heated with AC plus humdinger pot. Filter capacitors are noble Bosch MP caps! This suggests that the amp comes from West Germany, the 2x RFT tubes are probably not original, as they come from the former GDR. I guess the amp was built in the early to mid 50s, check the Bosch caps, they have the date on them.

I don't have a schematic, but it will be similar to this DDR mic pre amp. Possibly the first EF12k is connected as a pentode and the second as a triode.

Trace the wires and make your own circuit diagram/ schematic, it's really fun and you get to know the device.

I'm curious...

Thread 'Funkwerk Leipzig MVT 4050 T tube mic preamp' https://groupdiy.com/threads/funkwerk-leipzig-mvt-4050-t-tube-mic-preamp.79882/

 

[lukas]

I redrawn circuits, and of course i know who made this pre, but this is a little riddle...dont see date on the Bosch caps...

 

[rock soderstrom]

Wow, interesting. The OPT got DC current on it's primary winding, no parafeed.

The pot is in front of the first gain stage, probably due to the NFB loop...

and of course i know who made this pre, but this is a little riddle.

Do you know the manufacturer? Or big secret?

dont see date on the Bosch caps...

Really, no date? Here it is January 1974.
Normally its the last line on the "bandarole"

 

[lukas]

Bosch caps have only "8F" sign.

ps....Bosch caps measured as good...

 

[rock soderstrom]

Bosch caps have only "8F" sign.

ps....Bosch caps measured as good...

Okay, I see. I stick to it, they are probably built in the early to mid-50s, before that Bosch capacitors looked different as far as I know, the cylindrical shape came later, see Neumann U47. The first ones had the square Bosch double capacitors, then later the axial types.

Your Lorenz LMV2/III is apparently the third version of this amplifier which was first built in 1939/40.

https://www.radiomuseum.org/r/lorenz_lmv2.html

( I guess the guys from the radiomuseum would like you information about this rare amplifier)


The history of C. Lorenz AG was strongly influenced by the events of the war and their consequences.

For a short time until about 1950, electronic gear were produced under the name Lorenz in both parts of Germany, but then Lorenz was socialised in the emerging GDR and merged into the VEB Funkwerk Dresden.

 

[rock soderstrom]

ps....Bosch caps measured as good...

LOL. This is the difference in quality compared to the GDR components from the same period. As you can see later in the thread I linked to, all the capacitors there were as dead as a doornail!

PS:

I bet LMV2/III stands for Lorenz Mikrofon Verstärker 2, Version III , as usual, very creative naming