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Monday, October 13, 2014

Making of a 300B Amplifier, Part 3 : Completed Amps


I know that many of you are waiting for my report about the Elrog 300B. Please be a bit more patient. I don't want to write out of the first moment of excitement. I rather live with the tubes for some time and give them a thorough listen. What I can say already: This is going to be very interesting!

End of last year I already built a set of single ended 300B mono amplifiers which was meant to be for testing the Erog tubes. So far I only showed the assembly of power supply and amplifiers. But the final part which shows the completed set of mono blocks is still missing. So here is my statement in 300B amplification:

A four chassis affair, monos with separate power supplies for each channel. The photo above only shows one mono block. The 300B is driven by a 10Y through an interstage transformer. Interstage and output transformers are made in Japan by Tango. In this case the transformers are from old production when Tango was still part of Hirata Electric. The interstage transformer is the fabulous NC20 and the output transformer is a permalloy core NY15-3.5S. The latter has not been made any more after Tango split from Hirata and continued under the ISO Tango name. These are very rare and unique transformers. With their 3.5k load they are ideal for the 300B.

Both the driver tube and the 300B are heated with DC for zero hum and to avoid any kind of modulation of the signal by the mains frequency. Due to the extensive use of chokes in both B+ and filament supplies each unit is still quite heavy, although the amp is split into 4 chassis.

Above one channel is equipped with Elrog and there other with Western Electric. The driver configuration brings out the best of the 300B in my opinion and is at least as important as the output tube.

So this is the ideal test amplifier to assess the sound of the Elrogs.

The signal section with WE 300B:

With Elrog:

After I finished the assessment of the Elrog tubes, these amplifiers will be up for sale. Drop me an email if interested.

So please bear with me for some more time until I post my findings about the Elrog tubes. These will most likely come in several parts as I gain experience with them.

Stay tuned!

Best regards



  1. Those look awesome. What is the input sensitivity?

    1. Thanks Josh!

      Input sensitivity is 1.75V for full power out (about 8W)
      This is achieved with an input transformer. so they need an appropriate preamp which has a low output impedance. They wprkd well together with my 10Y line stage.