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PostPosted: Fri Dec 14, 2007 6:29 pm 
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Holy Ghost
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The EF86 is notoriously microphonic. Although I have not had too many such issues, I was wondering what others had done to tame it.

I use NOS Bugle Boys and they really are excellent. I have put 3 silicon rings around mine and that seems pretty effective in a head, but I was looking for some socket mounting ideas too. Especially considering a Combo!!

Any Thoughts?

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PostPosted: Tue Dec 18, 2007 12:03 am 
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Coco,
I haven't built an amp that used an Ef86 (yet). I have , however read about the reputed microphonic attributes and in my mind set about to come up with solutions.
My thoughts are this:
If you could de-couple the base from the chassis, you could avoid most vibrations transmitted thru the base. Some builders use grommets on the screws. My idea is to mount the base to a large fender washer or metal ring. This washer would then be mounted into a hole in the chassis that is about .25 inches larger in diameter than the washer. How to do it? Make a mold of hard wood with a top piece and a bottom piece. each identical. They would have a circular groove cut into each half. The groove would be such that it overlapped the hole edges in the chassis and the base washer. A sandwich with the wood being the bread and the washer being the meat. The grooves would be pumped full of silicone, so when it cured the mold could be removed thereby leaving a donut of silicone that suspends the washer.
Does that make sense?

LeeMo


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PostPosted: Tue Dec 18, 2007 12:50 am 
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Holy Ghost
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Makes sense. I was thinking of making a 'gasket' of soft material (1/8" neoprene maybe). Then sandwich it between the chassis & socket.

EF86 exact substitutes: 6267, 6F22, CV10098, CV2901, Z729

Russian 6J32P EF86 = 6267 = 6J32P
Russian 6SH32P
Russian 6J32P / 6zh32pi (6Ж32П) tubes.

Different Pinouts:
6BR7s. They are low microphonic pentodes
EF83 as a substitute. Pin compatible. Different specs
EF806 as a substitute. Pin compatible. Different specs.
British CV4006 is a mil-spec version of the 6BR7, so should be extra rugged.
5879 less gain but not as microphonic as EF86.

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 Post subject: EF86 Isolation
PostPosted: Tue Dec 18, 2007 1:40 am 
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I saw this over on the 18 watt site when I did some searching for the same thing for an upcoming amp build. It is from Dan Boul from 65 amps.

"I too build an EF86 variant of the 18 watter and I've seen and done a few easy things to reduce microphonics.

1. Enlarge the tube socket hole slightly to mildly separate the socket from the chassis and put a large fiber washer between the tube socket and chassis.

2. Put rubber washers above and below the tube socket mounting screws.

3. Use Micalex tube sockets for the EF86 (they seem to be better at absorbing vibration)

4. Use a hi-fi style dampening ring on the tube, works great.

This all creates a "shock mount" that should help.

I've found that the new Sovteks and Svetlana's from Mike Matthews (Newsensor) are either great or soft right away. I've also seen plenty of NOS stuff be soft also. NOS doesn't guarantee low microphonics at all.

I'm sure there are many ways to mount the chassis, etc. to reduce vibrations. The EF86 is so sensitive that they will always fail a "tap-test", but that doesn't mean they are necessarily bad."

"I've experimented with very very complex shock mounting schemes and I've found out that it's really about the tubes. Certain brands are much more solid than others.

Second, it's important that you let the tube get hot for a long time the first time you fire it up. Don't turn it on and off often when you first use it. A lot of EF86 microphonics is caused by the spacers cooling off and shrinking. After they've shrunk, there's no hope. They will rattle. So make sure you burn the tube in gently and slowly before you run a lot of signal in to it.

Lastly, the most effective thing we've found at 65 is to use neoprene rubber washers on the tube socket to reduce vibration, we use 3 on the bottom and 2 on the top.

Also really helps to orient the tube horizontally instead of vertically. The regular 18watt chassis puts the tube about 2 inches from the back of the speaker. The concussion from the speaker just beats the **** out of the tube. Our chassis has the tubes horizontal like a JTM45 and that REALLY helped with the EF86.

But really, it's still about the tubes. Dr Z uses a standard tube socket, not shock mounted. Same with Matchless. They just have to do what we do . . . buy 100 at a time and weed them out. Strangely enough, I've noticed that Mullard's and Amperex's are really cool high gain tubes, but about a 60% reject rate, especially in a combo."


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PostPosted: Wed Dec 19, 2007 11:45 pm 
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Hi Guys,

In Morgan Jones' book Building Valve Amplifiers he suggests mounting sensitive tubes on a sub-chassis. The sub-chassis is supported, like a trampoline in a cutout in the main chassis by elastic cord. You'd need grommets in all the holes the elastic passes through on the chassis and the sub-chassis to protect it from the sharp edges.

Take care
dave


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PostPosted: Thu Dec 20, 2007 8:08 am 
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Holy Ghost
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Keeping in mind you have to remove the tubes from time to time makes any mounting design a bit of a challenge too.

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PostPosted: Thu Dec 20, 2007 10:42 am 
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coco wrote:
Keeping in mind you have to remove the tubes from time to time makes any mounting design a bit of a challenge too.


Hi Coco,

Rigging up the trampoline would present it's own challenge but then you'd need someway to support the sub-chassis while inserting or removing tubes. Solve one problem and create a new one.

Have you seen the Pearl Iso Sockets?

http://www.pearl-hifi.com/06_Lit_Archiv ... all_b1.pdf

They can be had for a mere arm and a leg at Parts Connexion.

http://www.partsconnexion.com/catalog/tubesockets.html

dave


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PostPosted: Fri Dec 21, 2007 2:12 pm 
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Holy Ghost
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Those are over the top sockets! Crikey!!

I have another idea.

Get a piece of square 1/8" neoprene (mousepad comes to mind). Cut the hole in the chassis big enough to clear the socket & holder. Cut the neoprene big enough to cover the hole and fasten it to the chassis with 4 screws. Cut a round hole in the middle for the socket & mount the socket on the neoprene square. Then fasten the neoprene square to the chassis. That would suspend the socket & holder on the neoprene and provide isolation from the chassis.

I have one of those thin mousepads begging for something to do!! :D

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PostPosted: Wed Dec 26, 2007 11:25 am 
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Coco,
I just ran across this at 18watt.com. It was drawn by Heink at HBamps.
http://www.18watt.com/files/ef86_quiet.pdf
I'm pretty sure that you have to be logged in over there to view it.

LeeMo


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PostPosted: Wed Dec 26, 2007 7:27 pm 
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Holy Ghost
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Thanks LeeMo, that is very close to my previous posting about suspending the socket & holder on a neoprene square to provide isolation from the chassis, proving there is nothing new!

Image

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PostPosted: Sun Jul 22, 2018 10:08 pm 
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SPAM!!


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