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>Question? As the emission of a tube drops, does the efficiency % (ratio
>of output to input) stay relatively constant? If the plate current simply
>decreases while the efficiency remains constant, then a simple way of
>comparing two tubes in a parallel amplifier would be to measure exhaust
>temperature of each stack.
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** A better engineering solution might be to select one tube that is
large enough to do the job. It is my opinion that doubling the
feedback-C by using two tubes is only an advantage if one is trying to
build a VHF oscillator.
>Even if the efficiency decreased a bit, the increase in exhaust
>temperature should not offset the decrease in plate input. Thus a weak
>tube would always have a lower exhaust temperature than a good one.
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** However, a full-emission tube with a higher-Mu and a lower ZSAC
would also have a lower exhaust temperature.
>Do any commercial amplifiers monitor exhaust temperature for more than
>simply determining if the blower is working (like the Collins 30S-1)?
>Perhaps efficiency could be estimated with such a temperature probe.
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>Not sure if the digital temperature probes would be affected by the strong
>rf field above the tube - even if outside of the amplifier cabinet.
>
** Since IR thermometers will read temp. though an exhaust screen, an
anode-cooler temp, reading should be accurate.
>Colin K7FM
- Rich..., 805.386.3734, www.vcnet.com/measures.
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