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Well, at least this one is D.C. coupled, and Thank God it has no Grid- (music!) STOPPERS! Tubes don't oscillate just by themselves-- crappy wiring makes them oscillate). Grid stoppers STOP MUSIC. This schematic is very basic, it is missing 4 additional chokes, local feedback R7 is a joke, C1 should be about 9 Super-High quality capacitors, ditto for C2, C3 and C4. R3 and R4 must be ONE resistor-- not two in series. This resistor had better draw about 15X or more-- than the 6SF5 plate current. R5 is critical-- it should be a Caddock TFO-20 or better quality. C4 should not exist-- use Choke-Input here-- it SHOULD NOT meet
"critical" requirements-- the lower the DCR, the better, the physically smaller the choke, and the larger the wire in it, the faster and more dynamic the amp is.. It is used as a retard-coil instead of critical inductance-- to scrub-off unwanted R.F., noise etc. The rectifier MUST see this retard-coil BEFORE it sees a capacitor. There must be a careful balancing act performed between lowering ripple, and listening to the amp.
One CANNOT build a S.E. amp like 1/2 of a Push/Pull. It will be a total Wuss-- nearly all are! The 5Y3 rectifier is a total dud. A 5U4GB will run this thing with FAR better dynamics..... A LOW DCR power transformer that is about 3 to 5X times the power needed is also basic to getting this thing to start making music. Chokes must be
high-current rated or they will rattle or try to saturate. The 6B4 tube is NOS-- and like all of them except the venerated RCA Single-Plate of old, cannot even begin to compete with modern tubes.
Dynamics WAY too low, distortions WAY too high.... Various R.F. chokes are also needed throughout the power supply systems, and are needed on the driver-tube's filaments. Since this type of amp is sensitive to induced distortions of all kinds, it is necessary to use only the best, most expensive parts. The thing will Wimp-Out on bandwidth if you ignore it-- for instance, it
won't have shimmering, deep and extended highs, but a good Push/Pull will.... Layout is super critical, also, NO component can be directly bolted
to the chassis, and that includes even decorative wood or aluminum panels! This means you have to invent ways to mount components where they
work at their best. You can't allow any wires, tyraps, chassis parts,
or other components to be parallel to-- or anywhere near anything that is
carrying power or a signal. Remember- since it is Single-Ended, it can't
cancel induced distortion or hum. If you arrange your circuit so that it
DOES have some distortion-cancellations-- then it will also cancel parts
of your music that are similar. People who can't hear extended highs won't even know it's happening, but your trusty analyzer will, and so will you-- over time. Over time is the clue. You'll never get tired of listening to it if it's really good. My own situation is unique-- I have really good music
inputs, and I also use these kinds of amps for Home Theatre. I demand and
expect Big-Time dynamics and explosive lows-- something people normally use subwoofers and subwoofer amps for-- or at least they Bi-Amp. I won't tolerate this because I learned long ago that all the amps in
a Bi-Amp or Tri-Amp situation MUST be the SAME amps, and must employ the SAME bandwidth capabilities. Not only that, but all wiring to the drivers
must also be the exact same stuff, and the exact same lengths. Interconnects and signal-shapers? Ditto! So why bother?! Just make one
amp that can truly do ALL of that itself, and get ALL of it right. Sounds WAY better that way! Not only that, but you won't tire of it-- ever. And that's really the biggest challenge-- can you answer all of them? --Dennis--
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