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| Inside the EQP-KT, click to enlarge |
We have an ongoing long term vacuum tube comparison going on in the High on Technology lab and some exciting early results are rolling in. Fully tested, graded and matched sets of 12AX7 and 12AU7 were installed in a pair of EQP-KT equalizers, replacing the stock Chinese “Bugera Selected” tubes (don’t you just love tube marketing). The results were shocking and impressive.
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| 12AX7 and 12AU7 in EQP, click to enlarge |
After installing the new Mullard tubes I ran both equalizers for 24 hours before I began listening tests. For listening I played full range music files I’m very familiar with.
I am going to cut right to the chase and talk about what happened after I replaced both tubes in both equalizers. The overall tone and performance of these equalizers went from veiled and difficult to discern accurately to tight and very active.
BASS, LF BOOST and CUT
The new tubes took the bass response from loose and swampy to precise, punchy and big. The Boost knob now makes itself very known in the mix when it gets up around #2 (on the dial) and it goes up from there all the way to wow too-much lol.
Doing the Pultec® style boost and cut at 100 Hz results in classic tones which were impossible to judge accurately before the upgrade. After the tube upgrade the bass overall is much more tight and defined (that’s a good thing).
TREBLE, HF BOOST and CUT
I’ve always been impressed by the HF controls on this budget priced EQP style clone and I’m both shocked and amazed by the positive changes which resulted from swapping the tubes.
- The HF Boost knob now has serious punch, bite and sting capabilities (massively improved).
- The HF Cut seems smoother and more progressive (previously it was thin and difficult to hear exactly what was going on without more in-depth A-B comparison testing).
BANDWIDTH
The Bandwidth control took on a more distinct and clear character after the tube upgrade. Before the tube swap the bandwidth control was difficult to judge exactly what it was doing. Without a good clean IN/OUT Bypass switch (which no EQP offers) there was very little definition and it was difficult hearing what was going on when moving this knob; it was more of a “I like it or I don’t” with no shading between these extremes. AFTER the tube swap the Bandwidth knob has a much more solid effect, especially when working the LF Boost or HF Boost knobs in conjunction with Bandwidth adjustments.
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| New production 12AX7/12AU7, click to enlarge |
EXTRAS
For both sets of these tubes I paid $10 extra per tube for:
- Balanced Triodes
- High Gain screening
- Low Noise screening
- Microphonic screening
- Matching
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Matching might not have been needed but maybe it was and why not, it was only another $2/tube. Raw untested tubes are currently $26.95 each so piling on the tests took them up to basically $37 each ($74 per EQP). For a stereo pair of EQP-KT it’s a little under $150 for the upgrade (free shipping, plus sales tax).
We are currently buying tubes from several different suppliers for comparison, both fully tested and standard untested. We’ll be discussing tube vendors in an upcoming article but one of the most important take aways when considering modern production tubes is this: if you don’t buy the additional full suite of testing from a trusted vendor then what tube do you get (when you don’t order the tests)? Would it be one of the tested tubes that did not measure up? I’m not implying anything nefarious or any intentional wrong doing. I’m merely asking the question, if a tube tests out of range early in the testing-process, I doubt they throw it away. Instead I suspect they go on to a pile of tubes that are referred to as “not fully tested” or “standard grade” and these might be the inventory items you get when you don’t order the test suite.
EPILOGUE
I’m not an audiophile-forum fanboy-junkie type! I normally don’t put a lot of value in tube swapping stories but the results from this EQP tube upgrade have been a game changer for me. Did tube rolling change this bargain EQP into a $4500 EQ? No, but it did take it from “pretty good” and “useful” to WOW, it’s got clarity and power I’ve never heard from any of my budget EQP (and that includes the AudioScape EQP pair with their “selected” NOS tubes).
I had originally intended on moving these tubes between the various EQP models we are experimenting with but now that I’ve heard them in the Klark Teknik EQP I’m never going back to the original Bugera tubes. I’ll be ordering up two more sets of fully tested 12AX7 and 12AU7 for installation/comparison in the AudioScape and Warm Audio EQP hardware. Stay tuned as this story develops.
Thanks for reading High on Technology, Good Music To You!
©July 2026 by Mark King, it is NOT ok to copy or quote without written permission from the author.
ONE MORE THING
I added this article to Guitar Amps because guitar players should know that similar sonic improvements could be expected after installing fully tested tubes in your amplifier. Back in the 1980s when I had a ProAudio Music Store I sold a LOT of Groove Tubes because they made a BIG difference in the performance. Dr K, my electronics mentor and tech supreme put a lot of smiles on Marshall and Fender amplifier owner's faces. For my own amps I've always paid extra for Mesa Boogie premium tested tubes.
Originally published 07072026
