Gibson introduces a new dimension in electronic sound versatility
Gibson promo sheet for the then-new ES-340TD from its launch in early 1969. On the face of it, the ES-340 was just another variant of the the now well-established thinline Electric Spanish range - but in fact there were numerous differences to 335. Firstly the construction. It shared the same hollow body (with maple centre block) and set neck of the 335 - but had a birch (rather than maple) body and maple (rather than mahogany) neck - perfect for a clean Natural finish. In fact some late 1968 Gibson literature offers a birch body and 5-ply laminate maple neck for the 335, which was not otherwise available with a Natural finish. This was at an additional (but unspecified) cost. In what numbers these birch 335s were produced is unclear; they may have all ended up as 340s.
But the most notable difference between the 335 and the 340 was the wiring, as highlighted in the publicity sheet above. Pickups are PAF style humbuckers in each, but with differing specifications. The 340 was fitted with two Gibson humbuckers, part numbers 13546 (back) and 13547 (front), especially created for the phase switching capability of the guitar.
The controls look like that of a 335, but anyone trying one in a store without prior knowledge would most likely leave quite confused. The three-way pickup selector switch, used by Gibson for decades is now a phase switch, with an extra 'off' position. In the 'up' position the guitar's pickups are in-phase. To select either pickup, the player would have to turn the blend control to either extreme, or have a mix of both pickups anywhere inbetween. The 'middle' switch position offers the guitar with both pickups wired out-of-phase. This requires equal outputs from each pickup; the blend control is disabled in this position. Finally 'down' turns the guitar off.
Have a look at some of the other promotional sheets issued by Gibson in 1969 here.