These are the main amps used from July '69 to November '71. One was a 100 watt, the other a 50 watter. They first show up in July 1969 for the start of the 3rd American tour. From July '69 to September 1970 the only show where the JP Hiwatt isn't on stage is the 1970 Bath Festival. Through most 1971 shows the Hiwatts are also still present, at times with Marshalls though. There's no evidence of studio use with them, not something I'd rule out though given the length of time he used them.
These amps were pretty much the SAP - Special All Purpose - Hiwatt with a few tweaks. Without getting too technical, there is more gain on tap due to the preamp configuration and aside from increasing gain the tone and feel is a little different from what you would typically get from a Hiwatt, more in the direction of a Marshall. The power section is a standard DR103 with the addition of a choke. There is a footswitch that goes with the amp that plugs into the XLR input. It's used as a volume cut with a single head and was used as a cathode follower line out which would allow you to drive one head with the other when the amps were daisy chained which Page seemed to do early on.
July 1969 - Newport Rhode Island
July 1969 - Vancouver
January 1970 - The Royal Albert Hall
Septemeber 1970 - Madison Square Garden (the footswitch in action)
March 1971 - Southhamption Uni. England (daisy chained with a Marshall)
May 1971 - Copenhagen
September 1971 - Japan
November 1971 - London
The real amp