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Revox A77 resuscitation project (extreme long term)

Marchbanks

Marchbanks

Hat and Beard member
‘Do you want an A77?’ my audio engineer friend asked, knowing that my hifi gear averages around 40 years old. ‘I’ve got two, and neither have been used for twenty years. They are just sitting around in my workshop - it would be better if you could put one to use. Take a look at it and pay me whatever you think it’s worth in Belgian beer.’

The next thing I knew he had powered it up (!!) and sent me a photo.

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‘The right hand spool needs some TLC’ he said enigmatically. ‘It worked when it was last switched on, though.’

I picked it up and took it home. I started to clean the marks off the front panel, then decided to look inside. Screws on the top securing the case very rusty. A bit of rust inside too.

I thought I’d do the front panel properly, so I downloaded the service manual to see how to disassemble it. First step, take off all the knobs. Can’t get the power knob off, the shaft is rusty, the knob is plastic and I don’t want to snap it. That will do for now.

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Tonight I’ll sit down with the manual and a glass of wine and decide whether to buy all parts for a recap from Mouser or buy a kit from eBay.

Good things:
It seems to be a factory MkIV HS model with the speeds printed on the fascia rather than added afterwards.
Virtually all of the printing is intact.
It powers up.
At least two of the motors work, apparently.
I haven’t paid anything for it (yet.)

Bad things:
Corroded chrome on knobs and switches
Switches and pots all in need of serious lubrication (at least)
Rust
Counter won’t reset
Wooden cabinet rather tatty, and veneer is falling off

My estimated value so far - three bottles.

Thanks to @337alant for his offer of help, suggested plan of action and links to resources.
 
Zombie said:
Get both for a sixpack, Use one as donor.
Click to expand...
He wants to keep the other ‘just in case.’ I haven’t told him yet that if it has been stored like this one it is more likely to go bang when switched on than work perfectly. And that’s even if it doesn’t have a rusty razor blade rattling around inside like this one did!
 
Marchbanks said:
He wants to keep the other ‘just in case.’ I haven’t told him yet that if it has been stored like this one it is more likely to go bang when switched on than work perfectly. And that’s even if it doesn’t have a rusty razor blade rattling around inside like this one did!
Click to expand...

He's keeping the better one then and offered you the donor. :)
 
Be very careful trying to remove the power speed switch knob. They are quite weak and spares rare and pricey. There was a guy selling 3D printed ones on ebay a while back but you need to remove the broken plastic from the original knob metal cover which is a thin aluminium pressing and reuse it. Try soaking some easing oil or WD into the knob shaft join first. I have a fair few good spares if you get the bug and want to restore the machine. I went the buy capacitors from Farnell etc route better quality than the ebay kits and worked out cheaper.
 
Pine Marten said:
Be very careful trying to remove the power speed switch knob. They are quite weak and spares rare and pricey...Try soaking some easing oil or WD into the knob shaft join first. I have a fair few good spares if you get the bug and want to restore the machine. I went the buy capacitors from Farnell etc route better quality than the ebay kits and worked out cheaper.
Click to expand...

Yes, the Al outer pulled off easily, leaving the plastic inner on the shaft (shown above.) Something told me trying to force this off would probably end badly! I’ll try penetrating oil or WD40 when I get a chance. And thanks for the offer of spares.
 
I have one that works perfectly (and a valve G36).

This machine is well worth the effort BUT only if the heads are in good shape.

The absolute priority is the caps on the motherboard, because they go short-circuit, and the RIFA little time bomb rascals that WILL blow up, you can be sure of that.
 
chartz said:
I have one that works perfectly (and a valve G36).

This machine is well worth the effort BUT only if the heads are in good shape.

The absolute priority is the caps on the motherboard, because they go short-circuit, and the RIFA little time bomb rascals that WILL blow up, you can be sure of that.
Click to expand...
I’ll be able to take a look at the heads once I get the front panel off, but that’s all I can do at the moment. Is there anything I should look for beside scratching or flatting?

Yes, the Rifa caps’ days are numbered.
 
A flat of more than 3 mm indicates well-worn heads, with a fair lifespan left nonetheless.
ReVox heads are quite soft, but I’ve never seen scratched ones.
Re-lapping is an option but not for the faint-hearted.

Listen to any motor noise.

The capstan motor is barely audible, even with the ear close to the machine. There shouldn’t be any whining noise.

Often brake bands have to be replaced too.

If spool motors are sort of slow at startup then replace both run caps.
 
chartz said:
A flat of more than 3 mm indicates well-worn heads, with a fair lifespan left nonetheless.
ReVox heads are quite soft, but I’ve never seen scratched ones.
Re-lapping is an option but not for the faint-hearted.
Click to expand...

I have managed to get the power knob and thus the front cover off this evening, and so managed to take a couple of pics of the heads. I would estimate the flat to be about 4.5mm on the record and 3.5mm on the playback. Is that good enough to carry on with the project, or should I stop now before I spend any more? (Just £35 so far.)

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The heads are worn out. They will produce a sound but they are really past their prime.
Sorry, I wish I had better news.
 
Yes those heads are right at the end of the wear groves so if there is any sign of the head gaps showing they are knackered
Just had another look at the Record head and the head gap is clearly visible
Summertone would be worth a contact though

Alan
 
Might be worth checking Ricardo.ch for spares, Revox parts occasionally come up cheap - I’m happy to purchase and send to you if you find something.

Richard
 
yes that head is opening up now - not a great sign - you can find newish second hand ones on ebay quite inexpensively however
 
i'm in the home stretch of a very DEEP resto on three PR99s (antecedent to the A77/B77) and very similar .. if you have any questions feel free to ask.
 
Thanks for all your ideas and support. But given the iffy nature of the machine in other respects (original electronics unused for 20 years, rusty switches and pots, corroded trim, need for a rebuilt cabinet - and who knows the state of the mechanics), the addition of knackered heads have made it a no-no for me. I think I’ll pull the plug on it. It’s a shame to lose the 7.5/15 facility, but I reckon I could do better with a B77 in need of rather less work.
 
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