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John N. Lumley

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About John N. Lumley

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  1. Well, in a nutshell, the diodes prevent the driver tube voltage sagging, when the power tube draws heavy current. If you Google "stopper diode", you find better explanations. rgds, JNL.
  2. Hi Mike, great idea! The TV damper-diodes give you a slow turn-on, and a low voltage drop. The oil cap gives you low DCR, and a very long lifetime. (if not forever) As you know, that first cap right after the rectifier is the most stressed cap in the whole amplifier! The Marantz model 2 amps used 2) 6AU4 then a 8uF motor-run oil cap. rgds, JNL.
  3. Ok, here's the 2) schematics in jpeg format. I'm still very impressed with the sound of these little and affordable mini-mono-blocks! It's all I really need to power my Tang-Band W8-1808 full-range drivers (93dB), that are in a 2-way system, with a Tang-Band 25-1166SJ tweeter (93dB). Hat's off to Maynard, again. rgds, JNL.
  4. Hello, I did not isolate the transformers from the chassis. I use star washers to bite thru the varnish used in manufacturing, thereby grounding them. I employed a 6W6GT 1/2 wave damper diode, right after the MUR4100E diodes. This provides a nice and slow ramp-up of the B+, and helps filter out diode hash. I also use UF4007 "stopper" diodes in series with both the B+ and the B++ rails. These prevent interaction between the two stages, and improve the bass. I used 47uF-470uF-47uF caps in the power supply, based on PSUD2 simulations. I measure under 1mV-AC at the speaker terminals. Overall, a very worthwhile project, proving again that the circuit design is paramount! Expensive "audiophile" parts can't fix a bad design sound. A schematic will follow; still having to reset my password every time I try to log-on again... rgds, JNL.
  5. Hello again, here's a few external pix to start with. Front view first. rgds, JNL.
  6. Hello, I just completed a pair of "Little Sweetie" mini-mono-blocks, based on Maynard's great design. I basically used the same Hammond iron, but added a choke to replace R10; the 180-2W resistor. I also added a damper-diode tube in series with the red/yellow C/T wire, in the ground rail to provide a slow-turn-on. I put a stopper-diode in the B+ rail to the blue wire of the output transformer. It took me a very long 3 days to machine the chassis and wire the amps! And upon first start-up, they sounded really nice, and are improving every day. Thanks again to Maynard for sharing his wonderful designs and providing help to builders. (I will try to upload photos when I figure out how to resize them below the 2MB limit.) rgds, John N. Lumley
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