Have you picked out the machine yet? 78s machines range from machines which play-back records acoustically with a needle and fairly heavy soundbox on the tone arm to modern machines which can play back the records in a more gentle manner with an electrical pickup. Traditionally 78 RPM records were pressed into a fairly hard shellac material which could tolerate the heavy pickups. Around the late 20s and early 30s 33 1/3 RPM records started to appear which were made of similar material and had similar wide grooves. Slowing the spring motor on an early machine by modifing the governor to play these early transcription and movie sound discs would probably be fine however you should never put a vinyl Lp on such a machine. Also by the 1940s vinyl 78s started to appear. Those records also should be kept away from the old acoustic machines.
If your interest is in modern Lps as well as old 78s there are modern players which will play 78s as well as Lps. Be sure the player has a pickup cartridge which will accept microgroove styli (needles) as well as standard groove styli for the 78s.
If you want an old acoustic machine (I would love to have one) by all means buy one but keep your Lps as well as vinyl 78s away from it.
Tell us what you are wanting to do and there are many here who can advise you.
aveey_marie wrote:Im looking to buy an antique turntable that plays 78s. I was wondering if its possible to change the speed to play newer records at 33. Any help would be much appreciated!