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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 9th Jul 2017, 9:07 pm   #1
ricard
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Default A77 pinch roller source

The other day I was given (!) an A77, albeit in a slightly sorry state. Quite dusty, panel looks a bit tarnished. Surprisingly this is the version with built-in loudspeakers, but apparently missing the lid (the latches are there on the speaker grilles).

Haven't powered it up yet, but I immediately saw that the rubber on the pinch roller is severely cracked. Is there a good source for replacement rollers, or would it be better to have an appropriate specialist put new rubber put on the existing one?
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Old 9th Jul 2017, 9:14 pm   #2
Ted Kendall
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Default Re: A77 pinch roller source

Try Nagravox - I had a B77 pinch roller from them which is absolutely fine.
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Old 9th Jul 2017, 10:35 pm   #3
Michael Maurice
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Default Re: A77 pinch roller source

Try this company in Germany
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Old 9th Jul 2017, 10:51 pm   #4
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Default Re: A77 pinch roller source

Quote:
Originally Posted by ricard View Post

...the rubber on the pinch roller is severely cracked. Is there a good source for replacement rollers, or would it be better to have an appropriate specialist put new rubber put on the existing one?
I guess it depends on how important it is for the roller to match original factory specs. I'm not sure how easy it is for a manufacturer today to obtain and match the manufacturer's original hardness specifications for the rubber material. Where would they find an unused original sample which after many years had not changed its original hardness?

Also I think the original A77/B77/PR99 pinch rollers have a convex face as it presses the tape against the capstan shaft. So unlike other designs, I believe the Revox pinch roller only touches the tape and not also the capstan shaft on either edge of the tape. Pinch rollers sold today may or may not have that feature.

Maybe the source Michael suggests would be worth trying.
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Old 9th Jul 2017, 11:58 pm   #5
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Default Re: A77 pinch roller source

Can't help with the pinch rollers, but you had better change the five Rifas and perhaps the frako caps on the amp modules! I did one last month and the 15mm preset pots on the preamp cards fell apart. So there is always some ork to do with these decks.
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Old 12th Jul 2017, 6:03 am   #6
ricard
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Default Re: A77 pinch roller source

Thanks everyone. I would think that there would be some professional restorer out there who has managed to match the original rubber and shape, especially on such a classic machine, nevertheless, the company that Michael mentioned does seem to have them so I might try that route after having ascertained if the rest of the machine is ok.

Heck, at this point I don't even know which version it is...(MK I, II etc).

I did have a look at the chassis, and quickly realized that the obvious reason for the lack of functionality was that not only was the mains fuse missing, so was the fuse holder cap! The original fuse holder seems to be mounted both with rivets and a nut (Swiss meticulousness?), so it would be a bit of a pity to replace it, on the other hand, an original cap might be very difficult to find.

Anyhow, after having measured that the mains current was acceptable and then temporarily bypassing the fuse, I did a quick test with no tape. The motors seem to work, as do the breaks and pinch roller arm. Capstan speed seems a bit erratic for several seconds but then seems to settle down to something that sounds stable. Nothing lights up on the panel. I also noticed that one of the PC board fuse holders has split at one end, so the top fuse on the power (?) board (630 mAT) does not properly make contact, so that needs to be looked at to start with.

The heads looked fairly worn, but I'll have to look again; I didn't initially realize that they had relief grooves (or whatever it's called when the area of the head outside the tape has been machined away to minimize tape creep as the head wears) so I thought they looked very worn.
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Old 12th Jul 2017, 7:52 am   #7
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Default Re: A77 pinch roller source

Prime suspect for erratic behaviour is the main +21V supply. Heads are OK up to about 4mm flats - some go on further than this, but that's a matter of luck.

There's an identification guide on reeltoreel.de for the various marks, but briefly, Mk1 and 2 have silver fascias, Mark 3 grey with clear knob skirts, Mark 4 grey with chrome knob skirts. Mk 1 spool turntables are plastic, Mk 2/3 metal, Mk4 nextel-painted metal. Mk1 has a fixed gude to the left of the headblock - on later marks this is on a damped swivel arm. Heads changed from two-hole to one-hole mounting sometime in Mk2, and the much harder Revodour heads arrived some time in Mk3. Mk4 has a capstan card based on a 555 chip - earlier marks have a discrete version.
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