The EF86 is a high gain pentode designed to amplify low-level audio
signals. It is typically used as a preamp in audio equipment and
instrument amplifiers. Because of its design, the EF86 is much more
sensitive than other common preamp tubes like the 12AX7, and achieves
With all these good things going on, why don’t more designs feature this tube?
The reason is simple.
complex mechanical structure, combined with a high gain design, make
the EF86 very susceptible to vibration and the resulting microphonics.
triode has three active elements while a pentode has five. Most people
know that a 12AX7 is a dual triode, that is, two preamp tubes in one
small bottle. The EF86 is a single, very large preamp tube by
comparison. The EF86 also has an internal shield structure that is
physically tied to pins 2 and 7. There is a lot of precision hardware
that is carefully aligned to prevent physical damage or electrical
failure. Older tubes from Telefunken and Amperex used to flash metal
directly onto the base of the tube between pins 2 and 7. I can only
assume this was to reduce the number of physical leads inside the
bottle. The JJ EF806-S is a very good replica of a Telefunken and uses
this method today.
Here is a quote from an old Amperex data sheet for the EF86:
tube can be used without special precaution against microphonic
effects, in amplifiers in which the input voltage is greater than 10
millivolts, when the tube is mounted in the vicinity of a 5 watt
loudspeaker with an efficiency of 5%” The VOX AC-4 is the only guitar
amp close to these specs.
This tube was designed for radios, tape
recorders and home audio. Anything that has low volume or the ability to
isolate the tube from vibration. The EF86 made its way into guitar
amplifiers because it had a lot of gain and a good track record in
quality audio equipment. VOX, with the early AC30 is perhaps the best
example. You would have to talk with the original designers, but an EF86
can easily drive a signal through a simple tone control and high-cut
filter into the output section. If you take the tremolo and vibrato
circuits out of a vintage VOX using an EF86, that is exactly what you
Modern amp builders generally do not bother with this
tube because it is so hard to find one that will work in a tube combo
amplifier. There are a few like Dr. Z, Matchless, Bad Cat and VOX that
still use this tube, and that may be because those amps often have their
roots in classic British amps and EL84 output tubes. Some things are so
good; you are willing to put up with their shortcomings.
not lost, because there are things you can do to make this tube work.
There are no substitutes. If your equipment uses the EF86, you have to
like it enough to deal with microphonics or get something else. Vintage
Mullard design notes suggested using a tube socket that is shock
mounted. You will see this in old Gibson and Fender guitar amps that
used the 6SJ7 pentode,
but the market could use a good modern alternative. One way to do it is
to place small silicone O-rings between the tube socket and chassis.
This helps isolate the socket from vibration while maintaining good
electrical connections. Tube shields do not offer any reduction in
vibration and may make the problem worse. If your equipment has sockets
mounted to a printed circuit board, your only choice is to dampen the
If you cannot isolate the tube socket then your only
alternative is to add some treatment to the tube that will dampen the
vibration of the bottle. There are a number of ways to do this and the
cost varies from pennies to many dollars. There are a number of products
on the market designed for this purpose such as Duende Criatura tube rings. Others like Kryna,
also add passive heat radiation while dampening vibration. If you are
on a budget then you can buy silicone O-rings that you stretch over the
bottle or you can take a lead from Peavey and put a piece of heat-shrink
wrap over the end of the tube.
Thetubestore.com sells a variety of EF86 tubes
that will work in your audio equipment. It is important to choose the
one that will be best suited for your gear. If your equipment uses tube
sockets the have an extended base to accommodate a tube shield, you
should not buy the Electro-Harmonix or Tung-Sol
brands. The reason is that they are produced with a bottle that is
right at the maximum design width for a 9-pin miniature tube. If they
run on the wide side and the socket is off spec or has any dents, the
tube will be difficult to seat in the socket and microphonics may be
exaggerated. The JJ EF806-S, NOS from RFT, Tungsram and Tesla should be your group of choice. The JJ and NOS tubes are all around 20 mm while the EH and Tung Sols’ run around 22-23 mm.
JJ, Tung Sol and Electro-Harmonics are designed with a plate assembly
that is very similar looking to vintage Telefunken production. The plate
is about 13 mm tall, circular, made of solid metal with a single round
hole on one side and mica spacers on the top and bottom. The RFT and
Tesla tubes have taller plate structures and mica spacers that come
through the wall of the plate. This gives them a little more gain and
sometimes a little more noise.
The Winged C EF86 has a taller
plate that is similar to the mesh plate you find on vintage Amperex or
Phillips tubes. It is perforated metal instead of mesh but looks
similar. If you want an affordable alternative to Phillips or Amperex,
the Japanese Matsushita/GE EF86/6267
is the real deal with that delicate mesh plate. They were built on the
same equipment as the Phillips. If subjected to vibration, I find mesh
plates can be more prone to microphonics.
Here is a quick comparison / review chart of EF86 tubes thetubestore.com currently offers:
Tung Sol Gold*
A Bit Darker
A Bit Darker
A Bit Brighter
*Do not use with a socket that has an integrated tube shield element, ie. Fender style.
can see that some careful consideration will improve your chances of
making the right choice for your equipment. I have been using the EF86
in my amps for 20 years and just love the rich, detailed sound they
produce, and the negligible amount of hiss or hum. You can see my recent DIY amp project as an example.
are not at their best in combo guitar amps but if you follow my
recommendations, it will help. If you use a head only guitar amp, place
the head on something other than the speaker cab, or put a piece of
high-density foam between the head and cab. Audiophiles have been using
these tricks forever.
The EF86 is not for everyone, but if you need it, a thoughtful selection will help you get the best tube for your needs.