Microphonic Valves, is there a cure?

[Toppsy]

The Mullard ECF80 valves on my KaT6550 power amp have become very microphonic. Is there anything that can be done with these treasured valves to cure this?

They are fitted with 2-damping rings per valve. Though this has a little effect the noice from the valves can still be heard through my speakers.

Am I doomed to having to buy new valves? If so what recommendations, please.


Colin

[steve s]

Originally Posted by Toppsy

The Mullard ECF80 valves on my KaT6550 power amp have become very microphonic. Is there anything that can be done with these treasured valves to cure this?

They are fitted with 2-damping rings per valve. Though this has a little effect the noice from the valves can still be heard through my speakers.

Am I doomed to having to buy new valves? If so what recommendations, please.


Colin

hi colin, don't think theres much you can do.. i have a few of those i can let you have cheap.. pm if you interested

cheers steve

[Toppsy]

Thanks Steve, you have PM

[Ianm2]

Just to dispel an illusion, the dampers are useless.

The mircophony is due to the strucure of the valve vibrating, when tapped or via vibrations, the plates, wires, nothing to do with the glass.

Isolate from the floor.

Some old ones seem worse in this respect.

No little expensive rings goning to make any difference to this I am afraid.

[Greg.]

Another sweeping statement Ian?
I don't agree with you. In many valves the internal structure is in direct contact with the glass envelope. Have you never noticed that some valves are microphonic when first switched on and cold, but lose that microphony as the valve warms, no doubt owing to the minute clearances between the internal structure (mica plates) and glass being taken up by heat expansion. Damping rings do have an effect on sound, but you need to have the sensitivity of hearing to recognise the difference.

Best wishes,

Greg

[John Caswell]

Hi all,
I am on Ian's side here, one only has to look at the internal stucture of a valve to see that it is bound to be prone to microphony and no the internal structure is not in direct contact with the glass Greg, the grids are ellipsoidal shaped and sitting effectively in free vacuum only attached at each end of the major axis. Tahe a valve apart to see what I mean! The ECF 80 along with other valves WAD used are primarily RF types and nothing has been done to them to reduce microphony whereas EF86,7571, 12AY7 etc care has been taken. As for the ECC88 and 6AU6 well nuff said.
That should put the cat amongst the pigeons

John aka Dr John