Ampex VPR-6 Studio Editing Video Recorder
The VPR-6 was Ampex's last studio C format video recorder.
Introduced after the 'budget' 3rd generation VPR-80, it is a rather more sophisticated and expensive version of that machine. While the VPR-80 was a simple 'back to basics' product intended to be more affordable than the then current expensive and rather legendary VPR-3, the VPR-6 improved on the VPR-80 by having better slow-motion abilities and 'confidence' video and audio playback heads. All the studio machines were fitted with what Ampex called: 'Automatic Scan Tracking' (AST). This was a special video play back head positioning system that gave near-perfect slow-motion and still pictures. This at the time was a significant advantages over Qudaruplex video recorders. The VPR-6 could give 'perfect' broadcast standard video playback in reverse.
The machine shown here was built in 1988, and is standing on its own dedicated time base corrector (TBC-6) with front access door hinged down.
Such is the pace of change with this equipment that just ten years after it was built and with only 2,500 hours use, I was able to acquire this machine for less that one hundredth of its
new cost, and the owners were rather relieved to have sold it. I imagine that most of these beautiful and complex pieces of engineering ended up being just dumped in the skip.
Ah, at last a bit of heavy engineering.
Here we see the rear of the tape transport. Not that much to see as most of it is behind screened covers.
You may notice though, the ribbed main casting and the four cylindrical drive motors. The two in the corners at the top are of course the direct drive dc reel motors, which are driven by heavy duty MOSFET power amplifiers (screened box on right).
The brown cylinder at the bottom right is the video scanner assembly. This in itself is a complex mixture of motor, power amplifier, optical sensors, slip-rings, together with the electronics and precision engineering of the 'upper' video head drum at the front of the machine. To the left of the scanner is the capstan motor. I think bias and erase electronics are under the central screened box.
The lower picture is looking down into the power supplies. It's a while since I studied the manual, so I am not sure which box does what here. Fortunately it all looks fairly OK down in the depths...
I am reminded when I once was shown the insides of an Ampex computer tape drive, it looked a bit like this only much, much worse.
Another view of what a 'proper' video tape recorder once looked like.
This particular example, having spent its working life together with a VPR80 in a rack / console, has unfortunately lost its decorative cladding and heavy duty carrying handles - anyone have any to spare? This makes moving this system a bit tricky, as this machine is a two (strong) man lift.
One inch C Format machines are what are known as 'direct colour recovery' video recorders, which means that they have enough bandwidth to record the whole of the 5 Mhz composite colour video signal directly onto tape without any 'mucking about' that lesser analog (and digital?) systems do. (VHS for instance has less that half the bandwidth, and half the resolution of one of these machines.)
With lesser analog systems, horizontal resolution figures were (are) often quoted in place of their rather poor video frequency responses: 240 lines for VHS, 300 lines for SP Umatic, and 400 lines for S-VHS and Hi-8. By contrast, C Format bandwidth is flat to above 5Mhz and this equates with a resolution approaching 600 horizontal lines. Though one will need a very good monitor indeed to enjoy this level of performance.
However, while this is a wideband recorder and the transport a fine piece of engineering, moving a very thin flexible one inch ribbon of plastic against a wheel rotating at 3,000 RPM will introduce inevitable small timing errors. Unfortunately any slight instability will adversely effect the colour reproduction on playback, and therefore electronic correction of the off-tape video signal is required to obtain a stable broadcast quality colour picture. (In a studio environment the machine and its output will also need to be 'locked' to 'station syncs' as well.) This timing correction and synchronization is provided by a complex piece of electronics called a timebase corrector (TBC), which is mounted under the main machine in the above photo. The other box below the TBC is just a signal monitoring and switching unit.
It is important therefore if you are looking for a C Format recorder, to make sure that the machine comes with a correct TBC - otherwise YOU WILL NOT BE ABLE TO PLAY BACK COLOUR PICTURES (or be able to do any slo-motion effects as well).
In the beginning (say 1979), while rather known as 'a format without a tape', the Ampex and Sony one inch C standard rapidly became THE workhorse video tape format of thebroadcaster. While a great improvement in terms of cost of ownership and tape storage requirements over the earlier 2 inch Quadruplex recorders, these newer video tape machines were still formidable, complex and costly electro-mechanical devices. There is a serious amount of 'guts' inside one of these beasts, which may be seen in the various linked images.
Video tape recorders like these were quite tricky to lace up, required the regular attention of skilled maintenance engineers and consumed video heads about every 1500 hours or so. These heads, which cost perhaps the equivalent of £2,000 a set in modern money, might need replacing every couple of months if the machine was in heavy daily use. (Which of course how they were to earn their living.)
Fortunately, unlike domestic and professional video cassette machines, changing a video head was quite easily done in one of these beasts. I imagine it could be done in about 5 minutes, and no 'tuning up' of the electronics was needed either. In the picture below the transport cover has been hinged down, and the scanner cover removed.
Remember that the circular set of electronic and video heads on the left rotate at 3,000 RPM when the machine is working. One might like to ponder that when playing a tape the machine has to accurately line up a diagonal track of less than 1 mm width on a tape moving at several inches per second with a rotating magnetic head of similar thickness running diagonally across the tape at just under 1,000 inches per second. The video head is also vibrating at 400 times a second while being steered to produce the best output signal.
Easy!
Front view of the transport mechanics.
Interestingly, with all the electronics in this machine and the dual microprocessor control, what actually governs tape tension is the tension on a simple horizontal helical spring near the centre of this picture. It is probably a very nice spring, and it is hooked to a very fine pivoting arm with a very nice optical encoder...
While the transport has dynamic control of the heavy reels of tape, simple solenoid operated band brakes are used to halt the tape if the power goes off.
Actually the tape handling is very impressive in these machines. Not only is it blisteringly fast in the wind modes (at up to 500 inches per second if required), but the recorder knows 'where it is' on the tape at all times, and will not let the tape accidentally come off the end of a reel. So, if you are getting near to the end (or beginning) of the tape, the machine will slow down and stop the tape automaticaly to prevent any risk of damaging the delecate and expensive video heads. If you want to change tapes, instruct it so, and the machine will, as it approaches the end of the tape, slow the tape down, bring the scanner to a stop, and gently let the end of the tape come off the reel.
With assorted video ins and outs, 4 audio channels and various monitoring, timecode and control connectors, a studio video recorder of this era was quite a challenging device to hook up. Remarkably, on its own this system is incapable of playing back a tape...
It has to be supplied with 'station syncs', or at least a stable and correct video signal for its internal systems to lock to. Would you believe that these machines will not accept the non
EBU composite video output from a normal amateur camcorder?
However, it will inform you if a video reference is not connected. It will also 'advise you' if any other important signals are absent or of not correct quality. The machine also checks itself every few milliseconds, and will let you know if any of its internals are acting up or not communicating with each other. It will also tell you if the tape is not playing properly, or the mains are too high or low, or it is getting too hot, or if it is not able to 'optimize' the tape being played for correct editing.
Actually, as with the VPR-5, these machines have a clever self-diagnostic system built in. Obvious really if highly expensive television programmes and master tapes depended on these types of machine to be working perfectly. If a problem is detected, an LED lights up and an error code is displayed on the front panel. No difficulty if more than one 'problem' crops up as up to 10 out-of-range conditions or troubles can be 'stacked up' for later examination. Naturally if something major should happen then all proceedings are quickly and safely halted.
The circuit board under the deck and behind a clear plastic cover above, is the AST driver electronics. Automatic Scan Tracking was Ampex's clever dynamic tracking system that by means of a piezo electrically controlled video playback head (and a good timebase corrector), allows perfect slow-motion, still and reverse motion effects.
To keep track of the video track this system 'dithers' the play head across the video path 400 times a second (while the head drum is rotating at 3,000 RPM), and adjusts the crossing point for an optimum off-tape signal. Thus the head can be guided to keep up with the video signal whilst the tape is stopped or passing through the machine from X1 in reverse to X2 in the forward, direction. This variable speed playback feature was a great advantage for sports programmes.
To do all this though required a movable video head mounting that could continuously and precisely place the video head on a 1mm wide track while 'waggling' it at 400hz under a centrifugal force of about 1,000 G. Oh, and as it required some 400 volts A.C. to do this, there are some well insulated slip rings in the head drum. Simple!
Hence the clear plastic cover over the PCB to keep fingers off.
'Proper' professional equipment is usually designed to be fairly easily 'got at' for maintenance. With the Ampex VPR-6, much of the electronics is housed in a fold-out nesting unit. If this recorder was mounted in the correct racking system, it would also be sitting on a rather impresive sliding device that allows the whole machine to be pulled out of the front of the rack and then rotated sideways. The nesting unit can then be opened and the various guts attended to.
There are 7 large plug-in PCBs in the nest (the time code board has been removed in the above image), and various other boards lurk within the chassis. Most of the boards arereasonably accessible, as they rotate or slide out one way or another.
As with the VPR80, Ampex introduced some clever self-diagnostics as part of system control, that in addition to constantly keeping an eye out for absent signals, internal systems not communicating or out of range conditions etc, would actually be able to fault find down to component level.
Yes, with the aid of a special 'probe' that plugged into the CPU board, an engineer (in conjunction with the onboard microprocessors and front panel displays) would be able totrack down problems to individual components, or at least those in the digital systems.
Of course, this was in the days when digital was mysteriously new and designers were concerned that this complicated and new fangled way of doing things might prove rather beyond the capabilities of video engineers brought up in an analog world. This was in 1984 after all. (These days it either works or not, and if not you just throw it away.)
In the picture below I have pulled one of the boards out, oh and the screened item with the holes and writing on to the left of this board is the audio section in its own screened box. (4 channels, with Dolby A noise reduction as an option.)