This is one of the PE-Sennheiser-Telefunken joint venture amps. And
though looking pretty different, the EL86 amps (HSV25 or VKS203) are
built on almost the same chassis as the Sennheiser 254.
EL86 is a good working amp with a nice frequency response (could
have been worse with the tone controls).
"loudness style" frequency response curve is activated when pressing
the "leise" button. 2x10 watts RMS measured.