The RFT 12AX7

The Righteous Flame-throwin’ Tube
The RFT 12AX7
Photo by Kerry Beyer.
Photo by Kerry Beyer.

“…there is a time and place for that out-front spank, but if your mood shifts to slightly more mellow, there is a simple solution…”

Those who plug into Fender amplifiers from the classic “blackface” period know well the treble spike that makes up part of their signifcant character. Yes, there is a time and place for that out-front spank, but if your mood shifts to slightly more mellow, there is a simple solution, brutha’ man! Behold the little-hailed (but soon to be legendary) hero – the RFT 12AX7 – a rarely discussed/under-the-radar preamp tube that simply takes your tone and darkens it up, then breaks up early as all get out to deliver fat, greasy, semi-compressed mids.

In a couple old blackface Super Reverbs, the RFT conjures inspired, butter churnin’ glory. Same in all blackface amps – even the lowdown ’62 Vibrolux, and anything bright for that matter. Just slide one into V2 and dona’t forget to back up a few steps. Negative aspects? In the right amp, none, but this ain’t for tweeds (which would be kinda like puttin’ the Tabasco on jalapenos). Can you spell meltdown?

After ordering more than a dozen RFTs and testing them for months, a consult with tube wizard Mike Kropotkin, of KCA NOS Tubes, was requisite to find out exactly what in da’ hell is going on with this magical little glass beast. Enjoy. And remember, you heard it here!

So what’s the lowdown, Mike?

Tonally, they’re similar to short plate Mullards from the 1960s and ’70s with a smooth top-end – a bit darker than normal, but with the earliest break up of any 12AX7/ECC83 variant.

Are there specific brands we should watch for?

RFT 12AX7s are sometimes branded as RFT, Tesla, Telefunken, Tronal, Globus, Amperex, United and others, and some just with a funny symbol. Since all brand names can be found on different variants of 12AX7s, you have to know what to look for inside the glass. The plate structure is unmistakable; they have very short plates, which are unique. They look more like a Mullard/Philips 12AT7/ECC81 than any 12AX7/ECC83 I’ve ever seen.

Which amps best utilize the RFT’s characteristics?

They can work in any amp; they’re very unique and have a large cult following, but are not for everyone. They seem to work best when a player prefers lower-volume breakup and a somewhat darker tone. Many vintage Marshall 50- and 100-watt players use them to cool off their bright channels and get more breakup at less than window shattering levels. They’re also good in Fenders where the player craves more dirt at lower volume levels and needs to tame brightness.

Where did they come from?

They were made in East Germany in the 1960s and ’70s, and availability is relatively good right now⎯at roughly $20 to $40 or so. Right now, they’re among the very lowest-priced NOS 12AX7s around.

Austin native Nathaniel Riverhorse Nakadate has been held at gunpoint/machete three times, hit by two cars, and shot in the leg. He can often be found playing dirty slide guitar or sleeping alone on the cliffs of third world countries while chasing waves to surf.

This article originally appeared in VG‘s May 2008 issue. All copyrights are by the author and Vintage Guitar magazine. Unauthorized replication or use is strictly prohibited.

High Gain NOS ECC83/12AX7 Comparison

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