[78-L] Acoustic disc playback speed?

[Dave at Audio Tech Transfer]

Greetings from Wyoming,

One of my biggest frustrations with playing acoustic discs is trying to determine correct playback speed.  I'm aware of the advice to listen for certain notes, judge whether they're sharp or flat and adjust accordingly.  Which doesn't help as I'm not a trained musician and I don't have a clue.  I think I can get pretty close with recordings that have singing or voices, but instrumentals are a real challenge.

In doing research on various websites devoted to 78s, I've found advice (which varies) but often cites these guidelines:

Victor (early acoustics to 1909)          71.29 RPM
Victor (later acoustics 1909-1925)      76.59 RPM
Columbia (acoustic)                          80.00 RPM

The general consensus seems to be that Edison DD are 80 RPM and they do sound correct at that speed.

I'm just not sure about the Victors and Columbias though, and I don't trust my ears completely.  I'm currently transferring a large number of my 78s to WAV files in preparation for a radio show I'll be doing at a local college station.  So I'm understandably concerned about accuracy.  I also have the occasional customer bring old acoustic discs for transfer to digital, so customer needs are a consideration as well.

Any tips on arriving at correct speed would be appreciated.  I'm using Technics direct drive turntables for playback, so I've got capability to adjust pitch within a +/- 9.9% range.

Thanks,
Dave aka Cactus Cowboy