A Lenco idler drive turntable is a good choice because many 78s were not recorded at 78 rpm, but anywhere between around 60 to 90 plus rpm. The idler drive Lencos have a continuously variable speed between 33 rpm up to around 90 rpm. However, they are also something of a DIY project because they sound best modified and placed in a heavy plinth. If you are willing to do this, the Lenco models to be on the lookout for are L70, L75, L78, L88 and L99 (in Great Britain these models come with a GL prefix rather than L). If you are not willing to do DIY then a KAB 1200 which has been modified for 78 replay is a very good choice.
A couple other things to be aware of:
1) as Pryso has pointed out, 78s have varying EQs depending on the recording company, and, in some cases, on when it was manufactured, as some companies changed their equalization over time. This means that you need to have a separate preamp which has those varying EQ curves.
2) the specifications for 78 records in terms of inner groove diameter are different from LPs. Specifically, for 12" records, the outermost modulated groove diameter (where the music actually is engraved) is 146 mm for both LPs and 78s (aka SP = standard play), but the innermost modulated groove for LPs is either 60 or 58 mm (depending on the specification) whereas the innermost modulated groove for SPs is 48 mm. This means for a pivoted tonearm, that for lowest distortion using the Baerwald equations,the cartridge needs to be aligned differently for SPs vs. LPs.
For LPs (assuming 60 mm inner groove), the alignment null points - where the stylus is directly in line with the groove) are 66 mm and 121 mm, whereas for SPs the alignment null points are 53.2 mm and 112.4 mm.
Thus, if you want to play both LPs and SPs on the same turntable and arm, you will want a detachable headshell arm with separate cartridges for 33 and 78 rpm, because even if you have a cartridge that has separate styli for 33 and 78, you will still have to re-align the cartridge for lowest distortion when you switch between the two. Furthermore, you will need to use a headshell with screw slots rather than holes because the 33 and 78 cartridges will sit at slightly different angles in the headshell due to the differing alignment requirements. So for best results you cannot simply swap styli on the same cartridge and reset the stylus downforce (which is usually substantially higher for 78s than for LPs, say 4-6 grms for 78s vs. 1-3 for most modern cartridges playing LPs).
A couple other things to be aware of:
1) as Pryso has pointed out, 78s have varying EQs depending on the recording company, and, in some cases, on when it was manufactured, as some companies changed their equalization over time. This means that you need to have a separate preamp which has those varying EQ curves.
2) the specifications for 78 records in terms of inner groove diameter are different from LPs. Specifically, for 12" records, the outermost modulated groove diameter (where the music actually is engraved) is 146 mm for both LPs and 78s (aka SP = standard play), but the innermost modulated groove for LPs is either 60 or 58 mm (depending on the specification) whereas the innermost modulated groove for SPs is 48 mm. This means for a pivoted tonearm, that for lowest distortion using the Baerwald equations,the cartridge needs to be aligned differently for SPs vs. LPs.
For LPs (assuming 60 mm inner groove), the alignment null points - where the stylus is directly in line with the groove) are 66 mm and 121 mm, whereas for SPs the alignment null points are 53.2 mm and 112.4 mm.
Thus, if you want to play both LPs and SPs on the same turntable and arm, you will want a detachable headshell arm with separate cartridges for 33 and 78 rpm, because even if you have a cartridge that has separate styli for 33 and 78, you will still have to re-align the cartridge for lowest distortion when you switch between the two. Furthermore, you will need to use a headshell with screw slots rather than holes because the 33 and 78 cartridges will sit at slightly different angles in the headshell due to the differing alignment requirements. So for best results you cannot simply swap styli on the same cartridge and reset the stylus downforce (which is usually substantially higher for 78s than for LPs, say 4-6 grms for 78s vs. 1-3 for most modern cartridges playing LPs).