Single Ended Tetrode/Pentode design for KT61, EL33, Western Electric 349A, and all 6V6 types (selectable bias). Up to 5 Watts of clean power. The input tube can be a 12AX7, 5751, or 12AY7; Rectification can be done by 5Y3G/GT, GZ30/5Z4G, 5R4GY, GZ32, or GZ34, for HT voltage adjustment. The output transformers, made by Philips, feature an additional winding on the primary to provide extra filtering and local feedback to the screen grids, so this is not your average SET design; it also employs selectable global feedback. The circuit and layout are more highly evolved than its ancestor, my first foray into HiFi, a single ended EL95 design.
Top quality components throughout, many NOS: Three sets of inputs, with a NOS aviation spec Janco sealed ceramic "explosion-proof" 2P3T selector switch. Alps Black Beauty potentiometer. Custom Heyboer power transformer, Amphenol ceramic sockets, JBT and Microswitch switches, Dialco lampholder; Sprague Vitamin "Q" 196P coupling capacitors, Cornell-Dubilier 4uF paper in oil power smoothing capacitor; Sprague Atom, F&T, and Black Gate electrolytics; NOS Allen Bradley RCR carbon composition, Riken Ohm carbon film, and Dale wirewound resistors. All the wiring is silver plated copper in teflon: shielded for signals, and solid core for hookup... very little was needed due to symmetrical layout execution using ceramic standoff terminal posts, and an uncluttered design philosophy. It was built for both fidelity and longevity.
A look at the interior...
This amplifier shines with high efficiency vintage AlNiCo speakers, like Philips 9710M fullrange drivers, and Saba Greencones.
It has been functioning daily with stability and fidelity for over 7 years now, so here's the schematic: High Fidelity Stereo EL33 Amplifier Schematic
These can be more easily done with EL84 pentodes, the bias switch omitted, and feedbackcan be set at 22k for a happy medium between lively/forward, and extended/controlled.
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