Well, better late than never. I have an amp design to present, although I will include power supply and filament supply designs in a later post. First the particulars:
Power into output transformer: 20.0W/channel (≈18W @ the speaker)
Full power distortion: 5.9% (almost exclusively 2nd harmonic)
Incremental distortion: 0.29%/watt
Low frequency rolloff: 5.6Hz
High frequency rolloff: 25.2kHz
bias recovery (τr): 32ms (worst case)
Input sensitivity for full output: ≈1.6 Vac
A couple of important points:
WARNING: This amplifier involves VERY high supply and operating voltages. Voltages at this level are
IMMEDIATELY LETHAL! This is true even when there is no apparent current return path! Appropriate build techniques should be maintained at all times. Materials such as wire and shielding should be rated for this voltage level. Three wire grounded power connection is essential and ALL non-signal grounds must be directly tied to the chassis ground with a bonding resistance of not greater than 2mΩ. Service should NEVER be attempted with the amplifier power applied. Always ensure that power supply capacitors have adequate time to discharge before attempting servicing. Voltages must be measured with fixed instrumentation only. Never attempt to probe a circuit with operating voltages at this level.
In addition: this design is right up against the CCS limits for the 211 tube. There should be margin in ICAS service, but at no time should the plate voltage exceed the 1259V figure. Adjustment should be provided for in the power supply to ensure this operation. Also note that the power tubes are dissipating almost 100W each in pure heat. They should be positioned is such a manner at to ensure adequate convection cooling. Hot air rising off the tubes will draw in cooler air around the base. A minimum clear area around each tube of about 4" radius minimum to ensure adequate convection cooling should be maintained. The two output tubes also should not be closer than about 5" to each other (envelope to envelope).
For those not really interested in the design details, I'll put the schematic first:
Attachment:
Amp Schematic (small).jpg
Now for those of you who are interested, here are the load lines for the power and driver stages:
Attachment:
Load Line - Power Stage.jpg
Attachment:
Load Line - Driver Stage.jpg
As always, questions and comments are more than welcome. Please let me know what you think.
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