The 6SN7GT double triode valve is electrically equal to a pair of the 6J5 triodes in a single envelope. The construction uses a glass pinch and the two separate electrode structures are visible through the envelope. The wide glass tube envelope is 27 mm in diameter and excluding the IO base pin length, stands 63 mm high. Type 6SN7GT was first introduced in 1940.
The B65 Marconi-Osram audio variant with it’s distinctive metal clad octal base was first introduced in 1948.
The Mullard ECC32 ST shaped variant is perhaps the first variant as it was issued in late 1939, long before the advent of the Noval valve base and the dinky ECC83, the ECC32 was the valve of choice for low noise audio applications. Mullard describe the ECC32 as a double triode with separate cathodes for use as a paraphrase AF amplifier and in phase inverters. The electrode assembly although smaller than other double triodes of the period has supreme rigidity due to the glass pinch mounting mode. The curved anodes do much to increase surface area allowing impressive anode dissipation whilst enhancing rigidity and the sonic purity this can provide.
This Octal triode is favoured for many guitar and classic valve amplifiers, the most renowned being the Leak TL12 0.1 of 19467, however, it is surprising which other well regarded and modern exotica also demands fine devices of this type:-
Antique Sound Lab AQ1006 Mono Block amps
Atma-Sphere MA-1 Mk II.2 Amplifier
Audio Aero Prestige mono amps
Audio Note 300B amp
Audio Note conquest
Audio Aero Capitole
Cary CAD 300SEI
CARY SLP 05 preamp
Conrad-Johnson CAV-50 intergrated amp
Dehavilland Ultraverve linestage
Deja Vu Audio Type 45 amp
Modwright Sony 5400ES
Rogue Audio 99 Magnum
Singlepower headphone amp
VAC Renaissance 30/30 MKIII
Yagin CD3 Tube buffer