Digital counter for Revox A77, B77 & PR99 MK1

The counter can be used in any REVOX A77, Revox B77 and PR99 MK1 as a replacement and to upgrade the original mechanical counter.
The counter is plug & play. There is no need to intervene in the electronics or otherwise install additional sensors. Only 2 cables for the power supply have to be plugged in and the counter works.
The counter significantly enhances the appearance of the tape machines.

The counter can be used in any REVOX A77, Revox B77 and PR99 MK1 as a replacement and to upgrade the original mechanical counter.
The counter is plug & play. There is no need to intervene in the electronics or otherwise install additional sensors. Only 2 cables for the power supply have to be plugged in and the counter works.
The counter significantly enhances the appearance of the tape machines.

Operation of the digital counter for Revox A77, B77, PR99 MK1 (excerpt from the instructions for use)

Resetting the counter reading:
As before, the count is reset to 0000 or 0:00:00 with a short keystroke.

Conversion of winding count and belt running time *
Switching the display from winding count to tape running time and from tape running time back to winding count is carried out by pressing the button for a medium length of time.
The displayed time is calculated from the current counter reading, the thickness of the tape and the diameter of the take-up spool. In addition, the set tape speed of 4¾, 9½, 19 or 38 cm/s is deduced from the counting speed and the counter reading and the counter reading is converted accordingly into a tape running time * corresponding to the tape speed.

This display can only provide reasonable results if:

1. The counter at the beginning of the tape is set to 0000.
2. The counter is set to the correct tape type, i.e. the tape thickness (standard, long-play or double-play) and the take-up spool diameter (18, 22 or 26.5 cm). However, this does not necessarily have to happen at the beginning of the tape.
3. The actual tape speed corresponds to one of the four possible tape speeds. The belt speed is continuously determined and changes are therefore also taken into account during operation.

Tape type setting
For the correct display of the tape running time * the selection of the correct tape type is necessary. The setting is made with a long press of the button.
First the selected band type is displayed, then a brief press of the button jumps through the available band types.
With a medium-long press of the button (800 ms to 2.4 seconds), the selected tape type is accepted and the display jumps back to the meter reading or tape running time.

Tape type preselection:

• 26 LP: 26.5 cm (core diameter 114.2 mm), long-playing tape (35 µm)
• 26 dP: 26.5 cm (core diameter 114.2 mm), double play tape (26 µm)
• 26 SP: 26.5 cm (core diameter 114.2 mm), standard tape (52 µm)
• 22 LP: 22 cm, (core diameter 90 mm), long-playing tape (35 µm)
• 22 dP: 22 cm, (core diameter 90 mm), double tape (26 µm)
• 22 SP: 22 cm, (core diameter 90 mm), standard tape (52 µm)
• 18 LP: 18 cm, (core diameter 60 mm), long-playing tape (35 µm)
• 18 dP: 18 cm, (core diameter 60 mm), double play tape (26 µm)

Note: The spool diameter or the core diameter refers to the take-up spool. Important for a correct display of the tape running time * is the core diameter, not the spool diameter.

Brightness adjustment
The brightness of the counter display can be adjusted in four levels.
To do this, the counter button must be pressed when switching on the tape recorder (mains switch).
"HELLO" is shown in the counter display for the brightness setting.

The setting of the brightness levels is set by briefly pressing the button. The brightness of the display changes, at the same time the selected brightness level is indicated by the number of decimal points (1-4).
After selecting the brightness level, the device must be switched off and on again.

The installation and operating instructions can be found below under 'Documents'

Technical background information: Inaccuracies in determining the tape running time

The digital counter for the Revox A77, B77 and PR99 MK1, in addition to counting the windings, also offers the option of displaying the tape running time, unlike the analogue original counter.
Understandably, there are various reasons for deviations in the displayed tape running time:

• Deviations from the target speed
• Deviations of the take-up core diameter from the nominal core diameter
• Different lengths (and thicknesses) of leader tape (and thus larger core diameter)
• Deviations from the nominal gauge of the tape
• Slip during tape transport
• Inaccuracies in the counter (slipping of the drive belt, inaccurate translation)

Thickness of the straps:
The strength of the different belts, both from different manufacturers and within the product ranges of the manufacturers, varies with the different belt types (see table below).
This has a significant impact on the displayed time, especially towards the end of the tape.
In addition, you cannot rely 100% on the official information from the manufacturer's data sheets:
During the development of the digital counter with an Agfa PEM 268, which according to the technical data should be DP tape with a thickness of 27 µm, an actual thickness of 30.2 µm was measured (a winding with 500 turns with a thickness of 15 .1 mm or with an increase in diameter of 30.2 mm). That's pretty much halfway between the standard for LP and DP tapes(!).
The length of the tape resulted from the outer and inner diameter of the full roll (each without leader tape) and the tape thickness to 1281 m instead of the nominal 1440 m.
Accordingly, an actual running time of 112 minutes instead of 126 minutes was to be expected, and the measured running time was only approx. 30 s less.
From this it can be concluded that in this case the tape speed - rather coincidentally - was quite accurate.

Core diameter, leader tape:
Of course, the core diameter, not the outer diameter of the coil, is important for the correct time calculation.
But you can't always rely on it either:
For example, according to our experience, 22 cm coils from Braun have a core diameter of 100 mm instead of the standard 90 mm.
The leader tape changes the core diameter by about 1 mm, which also causes significant deviations.
We have taken into account an additional diameter of approx. 0.85 mm measured on an Agfa PEM 286.

target speed:
This is of course quite easy to understand. 1% deviation results in 1% time error, e.g. B. with one hour (3600 seconds) running time 36 seconds.

slip:
Slip is much more pronounced in devices without web tension control than in devices with web tension control and causes a higher speed in the first half and then a lower speed.

Examples:
A 26.5 cm long-playing tape with a length of 1080 m and a nominal thickness of 35 µm is assumed, played at 19.05 cm/s.
It has a nominal running time of approximately one hour and 34 minutes. Let's assume the following errors, each independently, each resulting in more displayed than actual tape travel time:

• Belt speed 1% too high (a more realistic value)
• core diameter 1 mm smaller (a rather pessimistic value)
• Thickness of the tape 1 µm less (very optimistic, in practice this is often much more)

then the following curves result:



The times shown don't seem to differ much from each other. But if you look at the difference between displayed and actual tape time, it becomes clearer:



It should be remembered that the deviations from the target speed were assumed to be more realistic, those from the core diameter pessimistic and those from the sliver thickness very optimistic.
In practice, the band thickness is very likely to be the main contributor to deviations from the actual time.

Tables of the nominal tape gauges of some past and presently available tapes

Normal (@ 19.05 cm/s, 26.5 cm: 720 m, 63 min)
Thickness (µm)	53	52	51	50	48.5	48
Manufacturer/ product	Agfa PEM 526 BASF LGR 51	Agfa PER BASF LGR 50 BASF SM 900 BASF SM 910 BASF SPR 50 LHL	BASF SPR 50 LH RTM SM 900	Agfa PER 525 BASF SM 911 RTM SM 911 ATR Master Tape	Agfa PEM 468 Agfa PEM 469	RTM SM 468

Long game (@ 19.05 cm/s, 26.5 cm: 1080 m, 94 min)
Thickness (µm)	38	35.5	35	33
Manufacturer/ product	ATR MDS-36	RTM LPR 35 RTM LPR 90	BASF LP 35 LH BASF LP 35 LHS BASF LPR 35 BASF LPR 35 LH BASF PES 35 LH	Agfa PER 368 Agfa PER 369 Agfa PEM 368 Agfa PEM 369

Double game (@ 19.05 cm/s, 26.5 cm: 1440 m, 126 min)
Thickness (µm)	29	27	26	25
Manufacturer/ product	BASF DPR 26 LH	Agfa PEM 268	BASF DP 26 BASF DP 26 LH BASF LGS 26 BASF PES 26	BASF DP 26 LHS

Sources: http://www.aes.org/aeshc/docs/basftape/basftapes.html , RTM (Recording The Masters ) and ATR Magnetics, LLC . Length and playing time from https://de.wikipedia.org/wiki/Tonband .

RTM is one of the last producers of tapes still available. Their production obviously came indirectly from the companies BASF and Agfa. Tapes from ATR (USA) are also still available. (Source: STUDER and ReVox Infoportal )