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Tubes / Valves All about our sweet vacuum tubes :) Threads about Musical Instrument Amps of all kinds should be in the Instruments & Amps forum

tubes & microphonic
tubes & microphonic
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Old 15th October 2018, 12:28 AM   #31
trobbins is offline trobbins  Australia
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Note that Jon Evans is updating the first part of that Mullard article soon, as it was missing the last page.

And Robert Gribnau just posted a link (Mullard Technical Communications - Nov 1962 - UK Vintage Radio Repair and Restoration Discussion Forum) to the associated article in Philips Tech Review http://www.extra.research.philips.co...960_61-071.pdf

Walter, as I see it, REW uses its sweep measurement process to get the required data to perform a waterfall analysis - John Mulcahy has certainly continued to advance the capability of that process over the years. The spectrum sweep can be abridged to the frequency span of interest, and can be made reasonably 'long' such that mechanical actions have time to build up, and then decay away. Although the use of a speaker to provide the acceleration force on the valve is not as 'direct' as a professional shaker table, or is it a linear relationship, I'd suggest it would provide a good qualitative assessment, and may be relatively easy for you to set up (although nothing is 'easy' when doing experiments).

Last edited by trobbins; 15th October 2018 at 12:31 AM.
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Old 15th October 2018, 01:18 AM   #32
nigelwright7557 is offline nigelwright7557  United Kingdom
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Quote:
Originally Posted by Galu View Post
Yout test proceedure is most interesting. However, it is the vibrations of the elements inside the glass that cause the issue.Hi-Fi News did a technical report on tube dampers, but found very little difference with or without the rings.

The following site explains the cause of microphony in valves and suggests what to do if it occurs: Microphony in Valves - What Causes it? - ampvalves.co.uk
The article says all valves are microphonic. I haven't found that.
I usually just tap them with my finger nail to see how microphonic they are.
I have had some success with rubber rings but not always.
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Old 15th October 2018, 01:37 AM   #33
trobbins is offline trobbins  Australia
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Many amps are nicely isolated from vibrations. Valve amps in radiograms, or on benches that also support a speaker (or even where the floor is wooden), and especially in 'combo' instrument amps, are exposed to vibrations. It's only when microphonic levels reach a noticeable level, or even howl from a feedback state, that people get annoyed.

Amps may have <<1% distortion, but few ever measure the amount of background 'noise' in their typical listening environment to see what spurious signals are in the background along with their music. Such background noise is easily masked by enjoyment of the music. And it probably invades many subjective tube-rolling tests with guitar amps, and biases personal opinion. It's not an easy issue to measure realtime, so isn't.

Last edited by trobbins; 15th October 2018 at 01:39 AM.
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Old 15th October 2018, 01:46 AM   #34
PRR is offline PRR  United States
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Originally Posted by waltube View Post
....the tool that Mullard use......
It was a standard Izod Impact test, scaled-down from when Izod proposed it to test brittle steel.
Izod impact strength test - Wikipedia
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Old 15th October 2018, 06:57 AM   #35
waltube is offline waltube  Italy
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The main goal is done because, in my opinion, the test results I found are, less or more, compatible with the ones made by Mullard and Philips ( they were same family so the test are quite similar) . Regarding the mic of the valve, yes each tube is microphonic in different levels just because their construction, no way. The level of the microphonic "noise" is related to the use; if I have a chain with 60dB of gain this "noise" can be heavy. The solution to isolate the equipment from base where is located is one way, the vibration (indirect stimulation) comes from loudspeaker are more invasive and the band of this vibration is much larger than the ones come from mechanical coupling (pavment+rack+box). If we tap on tube and no noise we hear this don't means that it isn't microphonic; there are "noise" over 10 kHz that is not so easy to ear and, in some case, aren't so low. As the test says.

Walter
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Old 15th October 2018, 11:55 AM   #36
jackinnj is offline jackinnj  United States
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tubes &amp; microphonic
Quote:
Originally Posted by waltube View Post
Thx, do you have some link of products?

Walter
Mide Technology | Engineering Solutions & Products
Piezo Systems: Piezoceramic, PZT, Piezoelectric Transducers, Piezoelectric Actuators and Sensors, Piezoelectric Fans, Piezoelectric Amplifiers, Piezoelectric Engineering, Ultrasonic Transducers, and Energy Harvesters
STEMINC

to name a few.

i have a piezo actuator from Mide, but it is now discontinued.
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