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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets.

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Old 17th Feb 2019, 7:32 pm   #1
julie_m
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Default Valve Microphony

I know what it is, and the lengths that were gone to to try to eliminate it ..... after all, the electrode structure of a valve is more or less a primitive seismometer.

But did anybody ever build a device that exploited the microphonic phenomenon usefully?
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Old 17th Feb 2019, 7:34 pm   #2
GrimJosef
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Default Re: Valve Microphony

Jimi Hendrix might argue that Jim Marshall did.

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Old 17th Feb 2019, 7:45 pm   #3
julie_m
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Default Re: Valve Microphony

Was that due to the valves, though, or the guitar strings being excited by the vibrations from the speakers?
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Old 17th Feb 2019, 8:38 pm   #4
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Default Re: Valve Microphony

Hendrix certainly used feedback via the guitar strings very often - that was something he could and did control in real time.

But I understood that the 'sound' of the Marshall amps themselves was put down, in part, to feedback via microphony in the valves. This can be changed by changing the valve type. The ECC83, for example, has both 'long plate' and shorter plate versions. I think the shorter plate ones were produced later with a view specifically to reducing the microphony (by raising the natural resonance frequencies of the structure to regions where the amount of acoustic noise driving them is less, at least when the noise is typical background). It's understandable that guitarists might sometimes want the amp to sound 'clean' and so would use a shorter plate valve, and at other times might want to have the microphony, and so use a long plate one. The long plate ones (which are rarer) certainly seem to attract higher prices.

Having just checked the Philips/Mullard type codes https://frank.pocnet.net/other/Phili...ListAB-v10.pdf for that valve I see that as well as the mC and I6 codes there's also a mention under f6 of an "ECC83 low microphony". Oddly it says "also CV4110" which is inconsistent since that's a version of the ECC88.

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Old 18th Feb 2019, 11:32 am   #5
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Default Re: Valve Microphony

In my days of playing with a rock band, the main criteria was the abillity of an amp to make a hell of a lot of noise...
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