Microphonic tube (ECC88) - how much is normal?

andow · Dec 3, 2018

I just finished a stereo version of a Gyraf Pultec and noticed that the tubes pick up every vibration in the room, which means that they are microphonic.

Now I know that this is normal to some extent, but I tried knocking on the front panel and saw that the loudest peaks are around -20dBu (noise floor of the unit is -80dBu)!

So my question is: how much microphonics would you consider normal for an ECC88?

radardoug · Dec 3, 2018

Not that much. Try another tube.

rock soderstrom · Dec 3, 2018

Thats too much of a microphone.

I guess you have to buy some new ECC88.

scott2000 · Dec 3, 2018

I've had issues with microphonics that weren't the tube's fault I'm pretty sure....... Just can't recall exactly what caused it......

gyraf · Dec 4, 2018

ECC88's are generally microphonic to some degree because of it's frame-grid architecture - and as there is no (easy) way to quantify the amount, it's more or less up to you to judge when it starts to get annoying.

When going through NOS mil-grade 6922's, I find some 10-15% to be unusable for audio..

Jakob E.

ruffrecords · Dec 4, 2018

My advice would be don't use NOS tubes, they are notorious for microphonics. Try a new 6922EH.

Cheers

Ian

andow · Dec 6, 2018

Thanks for your replies! I'm talking about Philips JAN 6922 btw.

I found that when just playing music over loudspeakers, the noise floor of one of the tubes rises from -80dBu to -40dBu! I would say that's definitely too much....

@Ian: are the new EH tubes less microphonic? And how do they compare sound-wise to NOS tubes?

weiss · Dec 6, 2018

Time to replace it. Just had to do the same with my 6386 :-[

gyraf · Dec 7, 2018

note that new production 6386 are VERY different from NOS ones..

Jakob E.

ruffrecords · Dec 7, 2018

andow said:
@Ian: are the new EH tubes less microphonic? And how do they compare sound-wise to NOS tubes?

Yes they are much less microphonic than NOS ones I have tried. Sound wise they are identical.

Cheers

Ian

weiss · Dec 7, 2018

gyraf said:
note that new production 6386 are VERY different from NOS ones..

Jakob E.

i was lucky enough to find a NOS

gyraf · Dec 7, 2018

Nice!

Also Billington in UK still have real and not-previously-deselected ones

(sorry for OT)

Jakob E.

Microphonic tube (ECC88) - how much is normal?

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