Microphonics (continued)

Hey.



I did what was suggested. I tapped the tubes with a pencil, and the one marked with the red arrow is really loud when i tap it. The thing that rattles was the cap right behind the left tube. Its allright now (Its a Jensen)

According to the manual the tubes are 6NI-P and EF86. Which kind is the one with the problem ?

Does anyone have one of each of these tubes in spare (checked for microphonics) Id rather buy from somone here who could check it up front than try and get one from a store, and the reason Im asking for both is that I wanna see if the other one benifits from being replaced as well..

Gustav

edit:got the photo working
edit edit:special points for whoever can reconstruct my face from the image in the tube (You know -Like they do in the movies)

I can't do the face, but the tube with the arrow is an EF86. They are high gain pentodes and are very sensitive. I'm not sure if it is a problem since it is so sensitive. Someone with more knowledge may be sure.

Anyway, how does it sound now without the rattle?

It sounds really good. Also did before, but the rattle kinda ruined it. It is VERY sensitive though, so I would like to see if it can be brought down a little so its not something I have to think about constantly when recording thru it.

Gustav

Have you tried putting an O-ring or two on the "noisy" tube?

Best regards,

Mikkel C. Simonsen

Whats an O-ring ?
btw..pultecs in the mail Mikkel.

Gustav

I wrestled with the EF86 for quite sometime.
I would buy a vintage bugle boy amperex, install it, the circuit would sound great for 6 months, then the 40 dollar sob would start to get noisy.
After about three tubes, I started to get a little pissed, so I mounted the tube socket on a pair of vynyl grommetts , played with the plate voltage and screen current, and now I have a tube that has been quiet for some time now.

I will need to open up the amp and see what i did, as i never document little tweaks like this, if you want the modifications.
cj

It would probably be way over my head, but thanks for offering.

Gustav

No.\
Way easy.
Reduce plate and screen voltage.
Try about 80 volts on the plate, this is done by increasing the plate resistance.
Then drop the current thru the screen by increasing the value of the screen resistor.
You can also tweak the pwr supply feeding the EF86 for lower voltage.
Those three things, plate volts, screen volts/current , and a mechanical shock mount WILL mekre that tube bearable.
Everything has it's cost.
The tube is a royal pain but it sounds like nothing else on this planet, once you make it happy.
cj :sam:

[quote author="Gustav"]Whats an O-ring ?[/quote]
In Danish: O-ring :grin:

It's a ring made of rubber. Not a rubber band (elastik), but a harder kind of rubber. You can also buy them as "tube dampers" but then they are expensive...

btw..pultecs in the mail Mikkel.

Click to expand...

Sounds good!

Best regards,

Mikkel C. Simonsen

You can get 0-rings from your local VVS guy. Or tear your kitchen apart :green: Not all of them will take the heat though. You can also get certified audio rubbers for 100x the price. :shock:

I dont get it at all..
you want me to put the o-ring where ? just around the tube ?
How does that help ? Im starting to think the easiest solution for a non-tech like me would be to keep it out of everythings way so i dont have to worrie about it.

Gustav

Yes, exactly! I can explain this better in danish; tænk på en stemmegaffel.. hvis du putter en elastik omkring den, så virker den ikke mere, same princip :razz:

[quote author="Gustav"]I dont get it at all..
you want me to put the o-ring where ? just around the tube ?[/quote]
Yes

How does that help ?

Click to expand...

Perhaps it doesn't - but it's cheap to test... It should dampen vibrations and make the tube less microphonic.

Best regards,

Mikkel C: Simonsen

an oring is a seal normally used in mechanical contraptions.

just a donut of rubber or other flexible material.

http://www.afmusa.com/orings.start.asp?OVRAW=oring&OVKEY=oring&OVMTC=standard

shows a few