The Illusionist

Since the 6P7S SE gave way to the 6P7S-i SE Amplifier the chassis of the former (lacking output transformers) was banned to the cellar.
6 years passed until recently I was chased by the DIY fever again and changed the output transformers of the Aikido driven 2A3 SE amplfier against new ones (but that is another story). I thought it would be a good idea to revive the original 6P7S amp using the TAMURA OTs. This is what it looks like now fitted with KT66:

Picture of KT66 Single Ended Amplifier with 6N3P SRPP driver

The octal socket was rewired for 6L6 family tubes and the like. The output tube can be one out of many 6L6 variants. I tried russian military NOS 6P3S, 6L6GA and 6L6GC from Sovtek, 6L6GC-STR from TAD (a remake of the Philips/Sylvania tube) and a JJ KT66. Yes, even KT66. The power transformer can easily manage the additional heater current required. The CCS assures the same bias current for all variations and the cathode voltage settles somewhere between -20V and -21V.
The connection to the OTs is made in ultra linear mode and the capacitance in the power supply was increased. Plate voltage is about 258 V (to ground) and the current is set to 45mA. It was of course an experiment, a crazy idea to put a KT66 or even a 6L6 to work under conditions traditionally more fit for an EL84. And surprise surprise, the TAMURA OTs provide an extra winding for NFB and soon I catched myself considering what a bit of global feedback would do (huhh). After measuring the open loop gain, the feedback resitor was calculated targeting a minute 3.5 dB of feedback.

The Sound

On B&W 703 speakers the amp delivers from low to high end a powerfull, rich and beautifully fluid sound on a ample 3 dimensional stage. The illusion of depth and width is such, that I considered calling this amp 'The Illusionist'.
The sound source: flac files out of a Raspberry-Pi with a PCM5102A DAC.


Schematic for 6l6 Single Ended Amplifier with 6N3P SRPP Driver
inserted by FC2 system