Nick said
Would be very interesting to see how well it would work, however one point I can think of is that I can imaging that a helical head is not as susceptible to the same sort of problems with stepping as vinyl. Or it may be that the stepping artefacts are easier to filter out with a low pass filter. I can certainly see how stepper motors will allow the head and the traverse tape motion to be synchronised though.
Indeed! I also didn't mention that the heads were mounted on flexible strips with a limited range of movement that were driven in position by a servo loop attempting to maximise the rf signal off tape and that the video once demodulated was fed into a limited range "timebase corrector" that effectively re-clocked the signal to line and frame rate...
However the slo mo aspect is relevant as the beast still has to track the linear track path to maintain the head position within the rf helical track path for the above to work.
In the analogue domain the video signal has to maintain a frequency response from about 5Hz to 5MHz so the opportunity for low pass filtering is minimal - this is one area where digital domain filtering has big big advantages...
As an aside - how did I discover the VTR had a mylar tape loop driving the capstan when the brochure describes direct drive capstan circuits? Well I was repairing a new but faulty VTR that the capstan wouldn't work on and instead of reading the manual I just pulled the schematic and worked through the direct drive circuit and couldn't find a fault...but it wouldn't work no capstan turning... so I decided the power bridge circuit driving the motor must be suffering from transistors with low Beta and changed all four for new... 2 hours later it still wasn't working so I called in the maintenance supervisor to see if he had an ideas as he had just finished the Ampex maintenance training course and I hadn't been on it yet. He poked his head into the machine and lifted out the broken drive belt and ask me if I thought that might be to blame... leaving me gob smacked.... took me months to live that one down...
I really want to try this for real now - another project to add to the list...
. Hopefully the electronics won’t be too taxing... otherwise I may end up bartering my skills ( cnc - horn building etc) for electronics help.