Several years ago, +GF+ Signet obsoleted their 2714-2717 pH/ORP electrodes and 3-2720 preamplifier. The old preamplifiers have been unavailable for years, however; electrodes were slowly phased out until the end of 2015 and will not be available once our stock is depleted.  Note: new electrodes will not work with the old preamplifiers.  We are happy to help you cross these over to the new models...