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Thursday, February 8, 2018

News from the ELROG Tube Factory 9


It's been quite a while since I published an update about the Elrog tubes. We had been busy catching up with orders and with the development of the new tube types.

The development of the ER50 and ER801A took more effort than expected. I am happy to announce that we have first functional prototypes.

It's always the details which cause throwbacks. What first seemed like a rather straight forward job by making the necessary adaptions to the 300B design, ended up in a complete redesign of the entire structure.

But it was worth it! The first 801A prototypes are shown in the pictures. amplification factor is a bit low but will be adjusted to reach the target value in production.

The filament spec is spot on at 7.5V/1.2A.

Some of the lessons learned from this development will also be used to improve the existing 300B design.

Here a screen shot of the prototype on the curve tracer:

It turned out as linear as a DHT can get. Exactly what we wanted to achieve. But what about the sound? Can it compete with the old production tubes?

First test in a linestage:

I am always reluctant with sound descriptions. All I can say is that I am very happy. Immediate emotional impact with the prototype tubes which are not even properly burned in. Unbelievably transparent and detailed.

Similar results in my 801A drives 801A power amps.

We will now make the first batch. It will take a couple weeks until they are finished, burned in, tested and printed. Then those who preordered will receive their tubes.

And now a few impressions from the production floor. Here we see a 300B on the sealing station. Here the glass bottom gets sealed to the tube.

These video clips show the process, here we see the internals getting inserted into the glass tube:

The sealing:

Then the tubes go onto the vacuum pump:

They are evacuated over night with the lid down and heated to a high temperature to drive all gasses out.

An ER242 fresh from the vacuum pump and powered for the first time:

ER845s in the burn in station:

Stay tuned for further updates from the production floor.

Best regards



  1. i seen nothing like this tube, wow!

    (edit;what does do the black stripe on glass?)

    1. That's our secret ingredient ;-)
      It serves several purposes which distinguish our tubes from all others

  2. wow, great work !
    The total height is the same of 300B ?
    Schoene Gruesse aus Mailand.

  3. Hi,
    That looks great but I have a 2A3 amp. Would you ever consider also making a 2.5V 300b? I'm sure your market for these tubes would skyrocket.