Elrog ER300B Vacuum Tube Review

Posted on 2nd March, 2021

Elrog ER300B Vacuum Tube Review

Eric Teh tries a brace of high-end tubes from this esteemed German marque…


ER300B (SGD $1,875 per pair)
ER300B-MO (SGD $3,380 per pair)
ER274B (SGD $840)

The Elrog vacuum tube company can trace its lineage directly back to the famous Telefunken factory in Ulm – a place of legendary status amongst collectors of thermionic valves. Unfortunately, Elrog fell on hard times in 2016 and had to file for liquidation. Its assets were purchased by Thomas Mayer, who has been able to continue the production of Elrog vacuum tubes with a new company – Deutsche Eletronenrohren Manufaktur GmbH. In this review, I sample his ER300B and ER300B-MO power valves, plus the ER274B tube rectifier.

Production under Mayer’s watch is said to be significantly improved in terms of quality and reliability. Thomas tends to do things differently, the most notable difference being the use of thoriated tungsten filaments instead of metal oxide. He says that these are less prone to contaminations as oxide coated filaments, explaining that “contaminations simply get burned off while they can ‘poison’ the chemical mix of the coating of other filaments. They also react faster to different current demands which results in better dynamics and resolution.”

Given that it is widely believed that such filaments work more effectively at higher voltages, I asked Thomas how it ties in with its use in the 5V filament in the 300B and 274B, for example? “The filaments of the 300B and 274B had to be 5V to be compatible and draw the same current as standard specification 300B and 274B tubes. There is the result that the ER300B, for example, has a slightly higher than standard 300B spec Rp because of this.” Thomas adds that Molybdenum has a much smoother surface than other materials and is less prone to secondary emission effects. This is why it’s common in high powered transmitter tubes and has benefits for relatively low powered audio tubes. When I pointed out that his ER274B design is unusual for using vertically stacked plates, he replied that, “we love to do things differently!”

Bill Jaensch - Managing Director of Sound Context Audio (Exclusive Distributor of Elrog in Asia)


I auditioned Elrog’s latest ER300B, ER300B-MO and ER274B tubes in my Concert Fidelity DHS-300B power amplifier. This is a single-ended design with one 300B power tube driven by a single 6SJ7 tube per channel. Rectification is carried out by a 5AR4/GZ34 tube rectifier. I checked with Concert Fidelity before using other tube rectifier models such as the 274B on hand. Each power tube was auditioned with my usual rectifier tube, a vintage Mullard Blackburn GZ34 with smooth plates. I then swapped the Mullard with the ER374B and repeated my listening tests.


Elrog’s ER300B is best described as a ‘300B compatible’ vacuum tube. It deviates from the original Western Electric specifications, noticeably in the use of thoriated tungsten for the filament and a maximum plate voltage of 600V. In contrast, the Western Electric datasheet specifies a maximum plate voltage of 450V. The ER300B has slightly higher plate resistance and transconductance, although I must say that I never had any issues with the ER300B in any 300B circuit that I tried it in. However, the ER300B is taller than a 300B tube, so please measure before you buy!

The pricing of the ER300B puts it firmly in the premium tube category. I happen to own a wide variety of 300B tubes, including a pair that’s even more expensive than the ER300B. Powering up the ER300B is a visual treat, with very bright illumination that makes a lovely light for your dim man cave – you have those thoriated tungsten filaments to thank for that!

The sound can best be described as agile, muscular and highly detailed. Users of entry-level 300B tubes are in for a shock when they experience the low-frequency tightness and heft of the ER300B, which has dynamics and slam in spades. Listening to Joe Hisaishi’s One Summer’s Day from Spirited Away, the orchestra built up the suspense and delivered the crescendo with power and control. Midrange reproduction was subtly laid back and organic while retaining an open and expressive quality. It avoids the honeyed vocal tone that some 300B tubes adopt in favour of a more modern and linear sound. 

I also enjoyed how the ER300B tackled high frequencies, with a very controlled and extended response. Cymbals were quick, clean and crisp but never harsh or bright. I use Hilary Hahn’s Partita No. 3 in E Major, BWV 1006: 1. Preludio as a test track for neutrality and tone. The violin came out searing, just as it should sound, and with the right amount of firmness and foundation. Coloured setups either render this track too nicely or far too hot in the treble, whereas the ER300B did it just right. Indeed, after extended listening periods with the ER300B, other such tubes tended to sound limp, hazy and slow in comparison. The ER300B is the proverbial iron fist in the velvet glove.


This is the prestigious, premium version of the ER300B, which uses Molybdenum as the plate material instead of Nickel. Visually, the plates of the ER300B-MO are shiny. The plates are also attached together using bolts and hex nuts. Apart from the plate material, all other technical specifications remain the same.

Tonally the ER300B-MO initially struck me as being brighter compared to the ER300B – this was in part due to the more open highs and tighter bass. The differences were quite easy to notice, even during casual listening sessions. This high-end tube also served up superior speed, resolution and expressiveness. I found this to be a double-edged sword, as in my system, the tone was thinner and brighter than I preferred. It’s still an impressive result, all the same.


The ER274B tube rectifier is pin compatible with common 5V rectifiers such as the 5AR4 and 5U4. It draws a filament current of 2A, which allows it to be used with most circuits without taxing the filament power transformer. However, the 274B does not tolerate large value capacitor input power supplies, so please check with your equipment manufacturer before trying the ER274B.

It has a DC output current of 225mA when used with a transformer input power supply and 160mA with a capacitor input. As stated above in my interview with Thomas Mayer, the ER274B is unusual as it features vertically stacked plates, unlike the common design where the plates are placed side-by-side. It also features a thoriated Tungsten filament, as expected from an Elrog product.

Many engineers have claimed that the rectifier has little effect on sound quality, and the differences we hear result from the change in voltage drop. This results in a modified plate voltage and operating point of the tube in question. However, my experience has been the contrary, and I have reaped handsome returns in experimenting with rectifier tubes. The ER274B instantly upgrades the performance of the ER300B. Indeed I would dare say that using the ER274B with the ER300B brings it dangerously close to the ER300B-MO. 

Comparing the ER274B with my Mullard GZ34, I got a much clearer and tighter sound. This is no mean feat, as the Mullard is highly regarded by audiophiles. The end result is greater with the ER300B, while the ER300B-MO showed a subtle but still noticeable improvement in sound. Interestingly, with my reference Concert Fidelity 300B power amplifier, I found the improvement was less pronounced when used with non-Elrog tubes. As an example, I tried the ER274B with Shuguang Treasure tubes and noticed only a modest uplift in sound quality.


Elrog tubes cost a pretty penny but are well worth the coin. In my view, they take a more modern approach to tone whilst retaining the strengths of vacuum tubes – midrange magic, three-dimensional soundstaging, dynamics, speed and authority. I believe the ER300B is the sweet spot in the range, so it earns an easy recommendation. The ER274B turned out to be a pleasant surprise, so I highly recommend it as a partner to the ER300B. The ER300B-MO requires careful matching to hear it at its best but should find its way into many high-end hi-fi systems – and rightly so. 

For more information visit Elrog


    Eric Teh's avatar

    Eric Teh

    Tinkering since he was a wee little Audiophile, Eric also collects fountain pens and watches. He is on a never-ending journey to find the meaning to life, the universe and everything.

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