"What microphones did you use to record your guitars?

I use a Shure SM57 positioned on axis a couple of inches from the cone. On some tracks the engineer, Ryan Hewitt, added a Royer R-121 ribbon mic, positioned about 15 feet away, in order to capture some of the room sound. We used a Telefunken Ela M 250 tube condenser mic on the acoustic guitars."

John Mayer was using the Royer R-121 Ribbon microphone while playing an acoustic version of "Something like Olivia". The microphone is slightly hidden, but can be seen at 1:47

Used for the guitar on Icky Thump, as stated by recording and mixing engineer Joe Chiccarelli in this October 2007 Sound on Sound interview.

“The Trident at Blackbird Studio D was used for monitoring, and also some guitar microphones, plus most of the room microphones. Some room mics went through an API 512, and a few through a crazy old RCA OP6 tube preamp. Most of the other close mics went through various Neve 1073, Brent Averill API 312 and Chandler TG2 preamps. Jack loves the sound of ribbon microphones, so we used a lot of them, on guitar amps, vocals, and as room mics: Coles 4038, Royer 121, AEA R84. I would have six to 10 room mics up, and would chose a stereo pair from them."

(...) “For the song ‘Icky Thump’ I had the Royer and an AEA on Jack’s two guitar amps, and a couple of U67s for room ambience. In a few cases I used the Shure SM7 guide vocal mic. Ribbons are prone to overloading, so we blew out four Coles mics on the guitar amps. Luckily Jack had several Coles 4038’s with him! The guitar mics went through Neve and Chandler preamps, and then always through an API 550A EQ, and then an 1176. The Univox sounded great acoustically in the room and was miked with a U87 across the room, going into a Chandler TG2 preamp and then some slight compression with an LA2A."

This is restated by Chiccarelli in this October 1, 2007 Mix Online interview.

The Twin was one of two amps that Jack White used, the other being a rare Silvertone piggyback amp. Chiccarelli used an assortment of ribbon mics on the amps, including an AEA R84, a Royer 121 and a Coles. He would also put a Neumann 67 back in the room for ambient tracks. As far as outboard gear, Neve 1073 preamps and UREI 1176 compressor/limiters were typically used, with a Fairchild compressor also being employed occasionally.

The Royer-121 was one of three mics used to record the guitar cab for Daft Punk.

Royer R-121 Ribbon Mics are part of the Green Day rig used by Billie Joe Armstrong. From the MIX article:

Armstrong employed myriad different guitars and amps, with a couple of Les Paul Juniors and a Telecaster once purportedly owned by Keith Richards getting the lion’s share of the work for the layers upon layers of guitar tracks. Dugan typically miked two of Armstrong’s 4×12 cabinets with two mics each: The first might have a chain that included a 57 and a Royer 121 ribbon, through Chandler Germanium preamps and EQs summed to one track though an Altec 1567A tube mixer; the other would have a 57 and a 414 through 1073 preamps treated the same way.

This mic can sometimes be seen on Matt's cab

in this article, Mac states his sound tech purchased several mics for the recording of This Old Dog, including a Royer R-121.

Used for "Get On Your Boots", as stated by producer Declan Gaffney.

"Most of 'Get On Your Boots' was recorded in Dublin by Richard Rainey, and the basic backing tracks were done live, by the whole band together. (...) Edge's thick guitar sound is entirely from the live band session, recorded with two Royer 121s, one on his Fender Deluxe and the other on his AC30, and the mics went through the Neve and then an LA2A, though it's not doing anything, it was just there for the sound. When recording Edge's cabinets, it's almost always a 121, or a Sennheiser 409, occasionally a 57. I record completely flat, because Edge will have found a great guitar sound, and you just record it."

The 121 was also used on Songs of Experience, as stated by engineer Math Bishop in this ProSoundWeb article.

“With The Edge I’d always have a Royer 121 and a [Shure] SM57 set up on the amp, and on these sessions I ran them through the Focusrite ISA 828."

Reverb.com commented on a video of john saying that he used a royer r-121 and a shure sm-57 in the video.

In this photo, Dave Mustaine uses R121 mic with Marshall Cabs.

This page includes photos of a Blink 182 recording session, and the captions confirm that a Royer R-121 was used on Tom DeLongue's cab.

you can see that josh use a rover r-121 for his marshall.