On the 202                        

Single ended amplifiers hold a huge appeal to those who get obsessive about the effects of phase inverter circuits on music waves The range of problems associated with getting power out of push pull circuits can cause bad sound to be a constant companion, rather than an occasional surprise. Some amplifiers were designed to be used with matched tubes and won't work acceptably without them. Since single ended places no phase related issues on the soundstage, it can sound pure and inviting.

The 202 was constructed around output transformers made by Philips, and utilized in a stereo integrated amplifier that Philips marketed in 1959-62 worldwide. Many aspects of the design of that amplifier can be found, but the 202 has no input or tone stages, has d.c. on the filaments and uses much larger values of filtration in the B+. The 202 puts 141 volts on the plate of the 12AX7 and 260 volts on the plate of the EL95. These values are lower than those found in the Philips. The negative feedback differs also.

There is no comparison between the Philips and the 202, which is completely silent. It can be used with loudspeakers that are over 100 dB/w without any a.c. artifacts. The 202 was constructed out of Philips parts of a quality generally superior to parts that were used in 1959, although the parts that Philips used were the best available.

The EL95, a puny version of the EL34, retains all of the characteristics of its larger brethren. It starts to harden up around 300 volts, and I might consider designing for 220 volts. This would necessitate a change in value to the plate resistors in both circuits, with attendant values that would be established by decreasing the downstream power supply resistance values to come up with the desired voltage point for the plate of the 12AX7. There isn't a specific point to work with, but tubes have operating ranges, and sometimes, like cars, they can deliver a lot of initial power. Higher voltages won't add to this subjective impression of power, and if the price of power becomes hardness, selecting a lower voltage point, a sensible idea of 'how loud' things will get, and you have a recipe for better sound, less heat, longer tube life.

The 202 makes a good headphone amplifier, and I tried it so on one occasion. I have a tube preamplifier that can drive my Sennheisers, but often eschew even that for a Sony TCK71 which, combined with its meters, serves as a valuable reference tool. The 202 is a versatile amplifier because its extremely quiet noise floor, coupled with its 5 ohm output impedance makes it capable of doing things like, for instance, drive a few meters of cable with aplomb, or a line signal around the world.

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