If you own an antique pedal harp, defined as one built before 1935, the following tips will help you enjoy your instrument, and will certainly help protect it from damage.,
Antique pedal harps have some characteristics in common, even though we are describing harps built over a span of 200 years. One should realize that there was a lot of very fine music written and performed on these harps. Despite the propaganda that one finds from the early 20th C these were very fine musical instruments, capable of subtle musicality that the stiff, overstrung modern harp cannot approach.
First, they were all handmade, though the later ones by Lyon & Healy and Wurlitzer had some of the roughing work done by machine. For that reason you need to understand that there are NO interchangeable wooden parts. On the earlier harps, even screws were not interchangeable between harps or makers.
Second, they were designed and built for much lighter string tension than the present “standard gauge pedal harp strings”. Installing modern standard gauge strings on an antique harp will result in structural damage, not only to the soundboard, but also to the rest of the structure.
Third, you need to realize that equal temperament tunings to a=440 is a relatively modern practice. Before the early 20th C equal temperament was uncommon, for in that tuning nothing is really in tune. The most common tunings for late 18th C and all 19th C harps was some form of meantone tuning. This varies with the maker and the time when the harp was designed, so it is wise to play with various tunings to find what your harp likes. The reference pitch in use during this period also varied. According to the best information we have today an early 19th C harp would have been designed to be tuned to a=420, plus or minus a bit. Most harps that have survived have the deep neck curve that would permit them to be tuned to a=440, but the earlier instruments, including virtually all the crochet-action harps and the early Ram's Head instruments are happier at the modern accomodation of a=415. This is necessary because the flat neck curve made the alto range strings too long to stand the tension required for a=440.
Fourth, realize that you are dealing with a harp that was made and used at a time when electronic tuners were extremely rare (Try finding an eectronic tuner from the 1850's!). Tuning was by ear, the machinery used in manufacturing was relatively simple, and the end result, especially with harps made before 1900, was a mechanism that was not as quiet as one expects from a new modern harp. Intonation was no better than the harpmaker's ear. This could actually be pretty good, especially on harps from the better makers, but don't get too uptight about intonation!
Over the last 20 years we have managed to simplify the stringing of these antiques. Thanks to the input from harpmakers in Europe, to the fortunate access to virtually un-played harps that had many of their original strings, to several antique string gauges, and to some basic trial-and-error, it is possible to string early harps with readily available strings that will not damage the instrument, and which give excellent sound. The following recommendations are a starting point. You may find them satisfactory, or you may start with the recommended set and modify it to suit your harp. Be very careful when increasing the diameter of a recommended string, for that will increase the tension required to bring it to pitch!
18th and early 19th C crochet-action harps: Standard gauge gut strings, two full octaves light. For the top octave use lever harp gut a full octave light. Wires are fiber-core, copper wrapped, from Vermont Strings. Use the Erard Grecian 6th 8va F-C as required. Use no wire core strings!
19th C single-action (Ram's Head era): Standard gauge gut strings, a full octave light. Wires are Vermont Strings Grecian set.
19th C Grecian double-action harps: Bow Brand or equivalent Lever Harp Gut. Wires are the Vermont Strings Erard Grecian set.
19th C and early 20th C Gothic harps: Bow Brand or equivalent Lever Harp Gut. Wires are the Vermont Strings “Gothic” set. These have bronze cores, and require more tension than the Grecian set, but they are a good match for the harp.
Early 20th C Lyon & Healy and Wurlitzer harps: Use Bow Brand or equivalent Lever Harp Gut. Wires are either the Erard Gothic set or the Early 20th C set from Vermont Strings.
It should be noted that the Lever Harp Gut strings presently available are a close match for the Erard 1829 string gauge, and are close enough to the Lyon & Healy and Wurlitzer string gauges that were supplied to harpists before WWI to work well. The transition to the modern “Standard Gauge” pedal harp strings and the stiff steel-core wires did not happen until about 1936. Earlier harps were equiped with much lighter strings. As a result they were much more responsive and easier to play.
Many of the 19th C harps were equipped with “swell doors”, operated by an eighth pedal. The effect is not that of a pipe organ swell box; opening or closing the doors has an effect on the timbre of the sound more then the dynamic range. On most harps the hinges are of leather or parchment. While interesting, the effect is so subtle that the doors and their associated mechanical parts were removed when the hinges failed. The only option was to remove the soundboard to gain access to the failed hinges so they could be replaced. Few harps that have survived with the original swell doors saw any significant use.