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Vintage Tape (Audio), Cassette, Wire and Magnetic Disc Recorders and Players Open-reel tape recorders, cassette recorders, 8-track players etc.

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Old 30th May 2022, 12:54 pm   #1
Restoration73
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Default Revox A77 top cover

The top covers I have seen have been grey plastic or brushed aluminium, the
latter used on the Mark 1 and Mark II versions I think. Can anyone provide
the definitive guide to the Mk 1 - Mk 4 covers ? TIA
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Old 30th May 2022, 3:47 pm   #2
Ted Kendall
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Default Re: Revox A77 top cover

Mark I-II - brushed aluminium, Grey plastic knobs with brights and transparent skirts, grey and red switch caps. Drive cover smooth finish.

Mark III - grey painted, knobs as above. Drive cover textured.

Mark IV - grey painted, drive cover textured. New knob design with lettering and numbered scales on knobs, bright skirts and knob centres, grey with white lettering. Bright switch caps with red spots as appropriate.

Spool carriers were originally light grey plastic, then bare metal and finally grey Nextel, which arrived late Mk III or MkIV.
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Old 30th May 2022, 4:06 pm   #3
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Default Re: Revox A77 top cover

Thanks Ted

I bought my first A77 second hand in 1980, an early (pre-Bauch) with light plastic spool
carriers, replaced it with a B77HS Sync (£660) in 1981. At the Audiojumble yesterday I picked up a complete A77 MkII HS for a mere £15 - although it "needs work" !
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Old 30th May 2022, 10:24 pm   #4
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Default Re: Revox A77 top cover

"The left reel motor does not work" - well it would if the drum not become stuck to
the brake band. Hopefully the machine will be working soon. Retaining the HS capstan
motor, I would like to make it run at 9.5, has anyone else tried this - running the tacho
at 400Hz ?
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Old 31st May 2022, 5:29 pm   #5
Ted Kendall
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Default Re: Revox A77 top cover

Perhaps it's best first to check that the machine has a proper high speed motor - some MkIIs did, some didn't. The motor should be offset towards the rear/top of the machine in the headblock aperture. If not, it's a bodge, which has been dealt with here recently.

If you want to make a three-speeder out of it, this may be possible with the MkII capstan card, depending on the gain available in the discrete front end. I've done this successfully on a B77 and an A80, but in the latter case I had to move the tach head as close to the rotor as I dared, as the output drops 6dB below spec with the halving of frequency. Be careful if you do this, by the way - both the tach head case and the nylon retaining screws are rather fragile by now.
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Old 31st May 2022, 7:21 pm   #6
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Default Re: Revox A77 top cover

It's an unusual find - so it's an A77HS Sync, with an official label (SEL-SYNC) on the grey
pushbutton, and the front panel with 7.5/15 legend. It is the early speed control and the motors dated May 1970,
so production that year. Even the head wear is not terminal.

It all seems to work, but I will replace the Rifa caps which are split as usual. Such a
version was popular for musicians. There is no evidence of any previous repair !
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Old 1st Jun 2022, 9:36 am   #7
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Default Re: Revox A77 top cover

The A77 is an excellent machine indeed, as I'm sure you know. I use two, a MkII four track and a later MkIV two track. They are standard speed versions. The MkII was the first one I bought and I liked it so much that I obtained the MkIV.

Both machines needed full servicing and it took me quite a while to carefully do this as per the detailed manual. It is impossible, unless you are very familiar with the machines, to do more than replace a few capacitors without the vital manual.

There are various sellers in Europe on ebay that can supply all parts needed. I replaced both pinch rollers, the brake bands and obtained the correct oil for the capstan motor. I also purchsed calibration tapes to set up the various levels and, in short, spent hours making sure everything was exactly as it should be. I set the bias for TDK AUDUA high-output low-noise tape as this is what I mainly use.
Anyway.... enough waffle, here are the machines....
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Old 1st Jun 2022, 11:43 am   #8
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Default Re: Revox A77 top cover

I will put up a pic when finished. I have polished the reel tables. Although I have the original manual, no sel-sync variant is given, so this is a rather neat aftermarket mod using a small pcb marked LAMB and a flat 4PCO relay.
Inspection has revealed virtually no head wear. I have just replaced the counter belt.

To quote Professor Stanley Unwin, "Deep Joy!"
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Old 1st Jun 2022, 11:47 am   #9
Ted Kendall
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Default Re: Revox A77 top cover

Quote:
Originally Posted by Restoration73 View Post
I will put up a pic when finished. I have polished the reel tables. Although I have the original manual, no sel-sync variant is given, so this is a rather neat aftermarket mod using a small pcb marked LAMB and a flat 4PCO relay.
Inspection has revealed virtually no head wear. I have just replaced the counter belt.

To quote Professor Stanley Unwin, "Deep Joy!"
That will be Lamb Laboratories, who were the UK agents between Hammond and Bauch.
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Old 19th Jun 2022, 3:32 pm   #10
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Default Re: Revox A77 top cover

Always busy here, but completion picture.

The Sel Sync facility (not track bouncing) allows the user to make the
initial recording on Channel 1 only, rewind and record a second track on
Channel II only, whilst monitoring the first recording via the Ch I record head and replay amplifier. It is a compromise as the record head has no cover and
hum is evident, and leakage of signal from the record head other channel,
including bias, has to be filtered off. It must have been popular as it was a
standard option on the B77. The Lamb advert is here;

https://worldradiohistory.com/hd2/ID...-04-IDX-15.pdf

Note my A77 required all 4 Rifa caps and 4.7 ohm resistors replacing.
Still, A77HS for £15 was money well spent.
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