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Another suggestion...

I don't know about current production, but historically the tubes in Atma-sphere amps were run very conservatively to maximize tube life and reliability. This is understandable, because of the erroneous notion that OTLs are "unstable" or "unreliable", and Ralph had to combat that belief among the ill-informed. However, in my own view the sonic performance of the amp can be improved noticeably by increasing the current used in the input voltage amplifier stage. This stage consists of a dual-differential/cascode with another tube used as a CCS in the cathode. To determine the amount of current, measure the voltage across the cathode resistor (Rk) of the CCS and divide the result in volts by the value of Rk in ohms. This will give the current in amperes. Then convert the answer into milli-amps. If the result is 4mA or less (meaning the current thru each half of the dual-differential circuit is 2mA or less), then you might benefit from doubling the current, by halving the value of Rk. Remember to select a resistor that can handle the power (P = {voltage dropped across Rk} X current). This was a tweak originally suggested by Paul Speltz, and I found it to work better than tube rolling to improve the sound of my amps. Even doubling the current still leaves plenty of headroom to assure long tube life.


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  • Another suggestion... - Lew 10:31:20 12/20/04 (0)


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