A1960s De Armond pickup that was part of the famous John Martyn acoustic guitar setup. Most commonly used on the Guild D55NT and his Martin D28.

From the John Martyn website

1-1) Early 70’s Live Set-up

Guitar – Initially a Yamaha FG (solid wood with the lacquered finish rubbed off). The FG series are still great guitars and relatively cheap!
Pickups – Initially no pickups and miked off the front of the guitar.
Then he used a DeArmond sound hole pickup and Barcus Berry (type) contact pickup positioned behind and slightly below the bridge. Both gaffa taped onto the guitar.

Around 72/73 he swapped the Yamaha acoustic for a Martin D28 and appeared on the Old Grey Whistle Test with Danny. The DeArmond sound-hole pickup up not stuck down by gaffa tape. The acoustic pickup was stuck just below and behind the bridge and cable taped down. DeArmond cable was routed sometimes below the sound hole and occasionally taped up and over the guitar.

To fit a De Armond you use the integral wire clamp on the rear of the back plate of the pickup and a locking slide latch on the bottom, under the volume control. This latch clamps the pickup against the soundboard from inside. These fixes can work loose, the sliding clamp damages the underside of the soundboard and loses contact pressure with use and then the pickup can move around and will get displaced if you hit it when playing. Hence the practical use of gaffa tape to keep it in place which he deployed on his Guild D55NT and Martin D28.

In the late 70’s he started to use a Guild D55NT acoustic guitar and toured with this for a few years. Not sure why he would switch from his Martin’s but it is a glorious-sounding guitar Small Hours was recorded using a D28 but from then on when Outside In was toured he used the Guild.