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SET Asylum Single Ended Triodes (SETs), the ultimate tube lovers dream. |
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SET Asylum Single Ended Triodes (SETs), the ultimate tube lovers dream. |
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In Reply to: Sure, run the 300B at a 45-like current to voltage ratio. posted by RC Daniel on April 3, 2014 at 15:52:12:
Once every year or two I post something along this line. Here it is again.
It's the relationship among the variables voltage, current, and load impedance, not the absolute values.
I use an arbitrary reference point of RL(ref) = (Vp/Ip) - 2.38*rp. This gives about 3% second harmonic at the edge of grid current, according to the WE table. A higher RL gives less power and less distortion, a lower RL gives more power and more distortion.
Most 300B amps operate at around 70% of RL(ref), giving 5%-6% typically. The traditional max-power point for a 45 is 275v, 36mA, and 4600 ohms. That works out to 1.28 times RL(ref); most people use a 5K transformer which is 1.39 times RL(ref). The WE table does not list such an example, but an educated guess would be less than 2% distortion if the 45 is as linear as a good old-stock WE 300B.
The other side of the coin is that, with a load of 2500 ohms the 45 would probably put out 3 to 4 watts - and sound like a typical 300B but underpowered.
FWIW, the classic 2A3 (250v, 60mA, 2500 ohms) gives 1.10*RL(ref) - also on the high side for low distortion, but not as high as the 45 specs.
For an example at the other extreme, WE lists 400v at 50mA into 3000 ohms. Distortion at clipping is about 10%, output is 11.5 watts, and plate dissipation is only 20 watts. That's 57.5% efficiency, theoretically impossible with a Class A amp - only the high distortion makes it possible.
I offer no interpretation, just the facts.
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Follow Ups
- RE: Sure, run the 300B at a 45-like current to voltage ratio. - Paul Joppa 17:45:26 04/11/14 (0)
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