/designs/437a---300b/ Recent content in 437A - 300B on Decades of Musings on HiFi Hugo en Mon, 02 Nov 2026 00:00:00 +0000 /designs/437a-300b-se-amplifier/ Mon, 02 Nov 2026 00:00:00 +0000 /designs/437a-300b-se-amplifier/ <div class="added y2026">This article first appeared in German on Jogi&rsquo;s Röhrenbude, <a href="https://www.jogis-roehrenbude.de/Leserbriefe/TH-Loesch-Amp/Th-Loesch-Amp.htm">300B-SE-Amp von Thorsten Lösch</a>. It opened with an apology for my &ldquo;pidgin German&rdquo;, after more than 15 years in English-speaking countries. This is my own English version.</div> <p><figure class="fig"><a href="front.jpg"><img src="front.jpg" alt="Photograph: the finished 300B amplifier from the front" loading="lazy"></a><figcaption>The amplifier from the front.</figcaption></figure> </p> <p>This amplifier started as a modification of the &ldquo;Billie&rdquo; kit from China (diyhifisupply.com). Apart from the case and the main iron, practically nothing was kept. The original kit is a perfectly decent cookbook 300B single-ended amplifier: a 6SL7 SRPP driver stage, a cathode-biased 300B at 400 V/80 mA, valve-rectified high voltage with CLC filtering, and the usual bridge rectifier plus 10,000 µF electrolytic for the heater supply.</p>