Richard,
I have the Dolby processor for the VPR-3, and I believe they sold
kits allowing it to be adapted to other machines as well. (The VPR-3 may
have had this adaptor connector stock.) There was also a dolby 'A' card
available for the VR-2B that probably replaced the factory audio card.
PBS would lend these out to stations submitting material to them on 1
inch.
The Beta story is a bit complex. On the old, oxide Beta tapes, you
could manually switch the Dolby function on and off, on the front panel.
it was up to the user to remember whether or not they used Dolby. On the
newer SP tapes, Dolby ws part of the improved standard. So, the Dolby
could not be switched off unless you have the machine in a maintenance
mode. Both the SP tape type and the required Dolby, were indeed detected
(together) by a hole in the cassette shell. The SP sense hole is located
just behind the tape access opening, in the center between the reels.
Hope this helps!
Tim Stoffel
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