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Wednesday, July 11, 2018

The New 845 Mono Amplifiers


After the introduction of the 845 amplifiers with indirectly heated driver, here are my new top of the line single ended 845 mono amps with directly heated driver.

For these amplifiers a new ELROG tube type was developed by Deutsche Elektronenröhren Manfaktur GmbH, the ER887.

Since the 845 requires a large voltage swing at it's grid an amplifier with all directly heated tubes would normally require 3 stages due to the low amplification factor of DHTs.

The ER887 is a large directly heated triode with thoriated tungsten filaments. A brand new tube type which did not exist before.

It has the same glass bottle and Jumbo 4 pin base as the 845 and runs with similar plate voltages.

It is a high mu triode with a plate resistance low enough to enable interstage transformer coupling.

Each mono amp has it's separate power supply:

Here we see one channel, PSU and amplifier:

The power supply uses a hybrid bridge with two ELROG ER274A and two 6AU4 TV dampers for the rectification of the plate voltage.

PSU and amplifier are linked with two separate heavy duty umbilicals, one for the high voltage and one for the filament voltages.

These amps got finished in April and had their debut at the High End in Munich where they were shown with some other amps.

The entire set of 4 chassis occupies a solid square meter of floor space:

This set will be shipped to Hong Kong for demo at the upcoming AV show August 10-12.

After the show they will be available for demo in the Hong Kong showroom.

Best regards



  1. awesome work as always. can you share the spec's on 887? Do you have a step-up transformer as the input, or this tube is capable of the large swing needed for 845. I am in the middle of thinking thru 845 monoblocks, and was going with 2 stage driver using triode C3g cap coupled to 6CB5A which would be IT Coupled to 845

    1. Thanks Sridhar,
      The 887 is reserved for my amps only and not available separately. The 6CB5A is a great tube for output but I don't think linear enough to be used as a driver for s linear tube like the 845. It would dominate the distortion as driver