Even though it has a similar pin layout and Octal-base as the 6SN7 family of tubes, is the ECC32 / CV181 the most musical sounding of preamplifier vacuum tubes?
By: Ringo Bones
Well-known as the output tube driver of the famed 50-watt Williamson Amplifier, the ECC32 or CV181 preamplifier or small-signal vacuum tube has such a gorgeous sound quality that’s, until now, still can’t be replicated by solid-state devices in the high fidelity audio world. As a dual triode in the 6SN7 family of tubes, it is not intended as a direct electrical replacement despite possessing a similar pin layout and Octal-base, but for situations where it does work, the ECC32 / CV181 – especially the NOS Mullard type – is one of the best sounding replacements you can use for any 6SN7 type preamplifier vacuum tube. Audiophiles admire it for really bringing music to life.
On average, the ECC32 / CV181 has a heater current that’s 350 milliamps higher than a 6SN7 tube – i.e. 600-mA versus 900-mA. The ECC32 has a slightly higher mu of 32 versus the 6SN7’s 20 and the ECC32 has a maximum plate voltage rating of 300-VDC while the 6SN7 has a higher maximum plate voltage rating of 450-VDC. On average, the plate resistance of the ECC32 at 14,000-ohms is twice that of the 6SN7’s 7,000-ohms, so it is not advisable to use high-capacitance interconnects / cables with ECC32 / CV181 vacuum tube equipped preamplifiers or it will result in a dark, murky sound. So the use of a Monster Cable M850i is out of the question.
Despite of the similar pin configuration and Octal-base, the ECC32 / CV181 preamplifier vacuum tube is not an exact electrical equivalent to a 6SN7 and should not be used to substitute a 6SN7 in preamplifier designs where the plate voltage could reach over 300 volts DC. The ECC32 may not work well in some applications where the negative grid bias is too high. Also, the ECC32 requires 950-milliamperes of heater filament current versus the 600-milliamperes required for the 6SN7 so the power supply transformer would have to be upgraded.
Despite these caveats, most knowledgeable DIY audio enthusiasts use the ECC32 / CV181 in place of the 6SN7 because the ECC32 vacuum tube has a gloriously rich midrange, smooth and open top end with very good bass articulation that, even now, still can’t be replicated using the latest ultra-wide bandwidth solid-state devices like FETs and bipolar transistors. Playback of recorded music just sounds more real with the ECC32 in a side-by-side comparison with the 6SN7 in its intended application. The 1950s era Mullard NOS ECC32 / CV181 types have a very well balanced sound from top to bottom. Great midband detail with zero harshness and never grainy – again something FETs and bipolar transistors still can’t do. The ECC32 / CV181 also have very good bass resolution but its bass is not extremely deep in comparison with the 6SN7 because of its higher plate resistance.
Despite of the vacuum tubes wide availability due to its use in pre solid state era missile and rocket telemetry gear – as in the US Department of Defense was rumored to have a 200-year supply of it during the Ronald Reagan administration despite of the overall vacuum tube scarcity in electronic stores frequented by civilians during the 1980s – the ECC32 / CV181 is only available in NOS (new old stock) from that dates from the 1940s and 1950s. Modern vacuum tube manufacturers from Mainland China and Russia and companies like Electro-Harmonix are, at present, not manufacturing their own versions of the ECC32 / CV181 preamplifier vacuum tubes.