Tannoy Vari-Twin MKII
The Tannoy Vari-Twin MKII is one of the rarer valve amplifiers to come out of the company's professional and broadcast line — a period piece from before Tannoy's name became almost synonymous with passive Dual Concentric loudspeakers. Documentation is scattered, and what survives lives mostly in service notes and collector forum threads rather than formal reviews. What the record does show is a genuinely unusual design: a bi-amplifier built around two independent amplifier sections, intended to drive the high- and low-frequency ranges of Tannoy's 12" dual-concentric drivers separately.
The amplification system consists of two independent amplifiers, which together drive a pair of 12" Twin Concentric units for speech and music reproduction. The valve line-up is substantial for the power on tap: four EF86 pentodes, two ECC83 double triodes, two EL84 output valves, and an EZ81 rectifier. The EL84 output stage is corroborated across independent sources. Frequency response is specified at 100 cps to 15 kc/s ±3dB, with hum and noise better than 70dB below rated output and distortion under 1% at rated output. The output transformer is multi-tapped for 4, 8, or 16 ohm loads. Power consumption runs 55–65 watts from a 110–250 volt A.C. supply.
Service notes from radios-tv.co.uk — one of the few detailed sources on this model — are emphatic about two things. First, when repairing the unit, the two power amplifier sections must be completely isolated and tested separately. Second, connecting the loudspeakers incorrectly can damage the amplifier: the high-frequency output must go to the tweeter and the low-frequency output to the woofer, never the reverse. The same source warns against connecting the low-frequency input to the high-frequency output. These cautions suggest the Vari-Twin MKII was a capable but unforgiving piece of engineering, one where a casual user could do real damage by miswiring.
One point of confusion in the surviving record: a Tannoy Vintage Yahoo Group listing describes the Vari-Twin as a "Three-Bay Distribution Amplifier." This appears to describe a specific installation configuration — three bays of speakers driven by the unit — rather than the product's fundamental identity as a bi-amplifier for twin 12" dual-concentric drivers. The more consistent picture across sources is of a valve bi-amplifier designed to work specifically with Tannoy's 12" dual-concentric loudspeakers.
Production years and original pricing are not documented in any source found. The MKII designation implies an evolution of an earlier Vari-Twin, but the relationship between the two is not explicitly spelled out in the available material. A period advertisement in Audio-Collection (????, p.94) highlights the Vari-Twin MkII as a product of Tannoy's experience and leadership, alongside the company's Monitor Dual Concentric Loudspeakers. What survives is a handful of forum inquiries from owners who recognize they have something uncommon and are hunting for schematics and service advice.
Known specifications:
- Type: Valve bi-amplifier for 12" dual-concentric drivers
- Power output: two independent amplifier channels
- Frequency response: 100 cps – 15 kc/s (±3dB)
- Distortion: less than 1% at rated output
- Hum and noise: better than 70dB below rated output
- Output impedance: 4, 8, or 16 ohms via multi-tapped transformer
- Valves: 4 × EF86, 2 × ECC83, 2 × EL84, 1 × EZ81
- Power supply: 110–250V A.C., 50–60 cps; consumption 55/65 watts
- Driver units: two 12" Twin Concentric units
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