Happy birthday dear EF86! It was a beautiful and sunny morning in the early summer of 1954 when this beauty saw the light of day in a robe of glass and expanded metal. This would be one way to start this story but here's come the twist of the plot, the small signal pentode was simply introduced to the market back in 1954 to provide high quality, highly efficient yet cheap amplification. This tube was manufactured in lots of varieties in terms of mechanical design and construction, and has been used in quite legendary audio gear.
For this 70th aniversary, I would like to share some examples from my tube collection with you, and maybe also a bit of history and technical background.
Let's start with the Valvo EF86. You might notice the outer shield that is build from a metal mesh. Some call it potato grater, however we'll see on other examples there's actually two kinds of mesh...
Now here's one produced by Rundfunk- und Fernmelde-Technik (RFT) in the GDR. It has a long, grey shield, no mesh. It looks indeed very similar to early units labeled Telefunken that I have seen on the internet at jogis-roehrenbude.de which is a great page btw.! However it should have been produced in East Germany, not in West Germany and also not in Russia.
The main reasons to use the EF86 was the large amplification factor (or should I just say "tons of gain") along with a very low noise (hum, hiss) and low microphonics. Microphonics is the (mainly undesired) situation, when a tube is stimulated to vibrate by external factors. It is causing the mechanical parts of the tube to generate noise.
But to maintain low microphonics, it is really important how the tube is wired and in what kind of environment it is operated. Basically we can say, the more vibration and the more gain that is squeezed out of the tube, the more prone it can be to microphonics.
This is an EF86 from TAD. The mesh looks a bit different, it is rather like the one on some russian derivates. Looking at the EF86 that had been produced by Svetlana resp. Sovtek I can't spot any diference.
One other reason why the EF86 was very cost effective was its heater design, so "AC heating" could be used which reduced cost for the otherwiese quite large capacitors needed to get a smooth DC voltage. Capacitors in that dimension where very expensive at that time, not talking about the rectifier (diodes) needed...
Here's the small signal pentode labeled Siemens. It has very likely been made by Valvo respectively Philips.
Why is the shield metal actually done as a mesh? Remember, it is is not the anode, it is a shield to protect the system from outer interference. It is the most prominent thing on this tube, "the face" so to speak. Having a mesh will definetely increase production cost to make the tube, so someone must have been convinced this is a good thing. But other manufacturers, like Telefunken, never used a mesh type shield. I was not able to find any explanation in literature or the internet. Does any one of you know or has any ideas??
The EF806S was eventually introduced in the very early 1960s by Telefunken as a more reliable and even better sounding EF86. Shown here is an EF806S made by Tesla in former Czechoslovakia. So I would expect this tube to be produced somewhere before 1992. It has a smooth shield like any Telefunken, wether it is an EF86 or EF806S.
One of the most famous devices where the EF86 or EF806S is working in, is the legendary Neumann U67 microphone that was introduced in 1960. It is one of the most used and most sought after microphones and it has been used on countless records and hits. And it is still produced by Neumann using an EF86.
Coming back to the buzzword "microphonics" that is often used with the EF86, those large diaphragm condenser microphones are placed in shock mounts while operated in recording studios which is a relatively "safe" environment. And probably the studio itself is also shock mounted like the legendary Galaxy Studios in Belgium. In fact the EF86 is running in triode mode in the U67 with moderate amplification which makes microphonics even less of an issue.
There's a handful of schematics (also published in the tube's data sheets) that intended the EF86 to be used in a microphone preamplifier, with high amplification factors. Those circuits have been picked up by amp manufacturers since decades and have been used more or less 1:1 in various guitar amps and combos.
Shown here is a recent production from JJ Electonics in Slovakia. JJ is probably using the machines from Tesla for making these EF806S and in fact the Tesla and the JJ look pretty identical.
Happy 70th birthday EF86! Part 7 - Telefunken just hits different, well at least it hits me with some instant vintage vibe just looking at the logo. The Telefunken is considered to be one of the best sounding if not THE best sounding EF86. It would only by topped by the original EF806S but these got very expensive over the last decades. So I was lucky being at the right place at the right time to get at least some TFK EF86 for a good price. To be honest, I mean I have put 2 or 3 in demo amplifiers that are out there, but in my opinion those EF86 (and definetely the EF806S) are best spared for a tube microphone or preamp. With one of those tubes, I would rather be recording Natasha Shneider's vocals than using them in a guitar amplifier. Sorry guitar amps, I love you, but there are limits. 🙂
In the majority of the guitar amp designs I have seen, it is tried to squeeze a lot of gain out of a single EF86. The pentode is then used in the first stage of the amp and probably it is the only gain stage feeding the power amp. While I understand the wish for having as much gain as possible, the drawback of this approach is really the risk of microphonics, basically in any environment with a lot of air or structure-borne sound that impacts the tube (e.g combos).
The Beausonic amplifiers also use an EF86 but for this design I tried to make things different, for sake of great tone in first place, but it will also curb microphonics. In Beausonic the EF86 is working in the second gain stage and is wired differently in a couple of ways. One result is the amount of gain that is achieved, it is fairly low. In this scenario the EF86 is a mighty tone shaping tool, creating a unique tone with lots of dynamics and and percussive attack. The necessary gain is created in the first stage by two triodes, again with very low noise, and this way we can push the EF86 for a very sweet and harmonic overdrive.
