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B77 & PR99 conversion - My first 'reel' post here..

marcochezzi

Active member
Joined
Jul 12, 2023
Messages
78
Location
South Africa
So for what seems like a lifetime, I have been watching my health, patience and humour decline thanks to a key client's inability to make +150 days payments, this despite their MD enjoying +R130 bar annual income, before benefits..

I am frustrated beyond words, not only in the seemingly nauseating capitalistic economies of scale, but in the absolute lack of common sense and general business ethicality that seems to prevail when large 'monopolies' take on the services of smaller vendors to further their ways..

So, when the chips are down, go into the garage, turn on the old lathe and mill and make more chips.. While it does not improve the financial situation, it sure as hell beats yelling at those that cannot or care not to hear, all day long..

I think its pretty well understood that I like to play on these old dinosaurs, I still have one Revox B77 which is fairly standard albeit with a lick of paint, and since I had purchased some of the key ingredients for a change some months back, the opportunity presented itself once more to finish the last of my stock, to the level which I want her to be..

Some history - The machine came partnered with a C270 that I had bought off a forum member what must be 2 years back, maybe less, come to think of it she might even have been on of the two I had acquired from FDLSYS a very long time ago, not sure, cannot really tell, but somewhere in her first landing on my shores in fairly sorry state to now, she was made over and actually worked really well, so why the hell leave her alone then..??

A while ago I decided to take an old B77, convert it to high speed 2 track, convert it to flat face, and then convert it to real time count, cause why, cause that's how I like it.. And so it was..

Then another while passed and I decided to try my luck at incorporating the PR-99 MK2 digital count and locator functionality into another flat faced B77 as an opportunity presented itself on facebook when the locator board and respective display and control card became available, followed by the headblock assembly which housed the original Revox count encoder wheel pulley thing.. And so it was..

And since there were two, why not go for three right, I mean, if not why not.. Cannot even remember if I had gotten in touch with the original locator board vendor and asked if he might just maybe have one more set in stock.. "yep", he said..

What about the headblock assembly?? "yep" he said..

So I got them, stored them in a drawer where they lay dormant for a long long long time..

Then by virtue of the powers of the audio Gods, and nature, I got to meet Charles, telephonically, because there were odds and ends that I needed, predominantly a complete set of brake bands for the B77 and I had stupidly trashed mine by dropping a 3 jaw lathe chuck on the assembly, by mistake of course, sending the lot to RTR heaven, and he happened to get in touch....

So after some mutual to and fro comms I made a much needed turn past Charles's place, where I was met by his lovely wife, a few nutty dogs and a plethora of beautiful valve jobbies that I would like to add to my collection too one day, not necessarily his, but if they go on the market and the green stuff is flowing a little better than today then who knows, just maybe..

Landed up driving away that afternoon with a set of perfectly functional undamaged brake bands, with the rest of a somewhat 'abused' mono PR-99 MK1 with destroyed audio electronics attached to the much needed braking mechanism..

This lent itself to some use, to which the third bastard musketeer was born..

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So yes, there was not much that I could use out of the recent PR99 aquisition, firstly it was a MK1 machine, which has no digital count mechanics, the damaged state of the electronics is clear in the pics below, probably eaten by mice or some odd copper alien UFO thing, the pinch roller assembly was rusted beyond use, the unit itself was mono, and quite frankly I needed the VU's for my first build as my originals were damaged, but, I could use the following for my build..

1. The headblock cover
2. The narrow sidepanels
3. The chassis standoffs..
4. the supply and takeup tensioner mechanism which beats building your own, for a third time..

The rest - all B77, well, mostly..


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So using the PR99 faceplate to try convert the B77 is of no use to me, firstly the faceplate is for an analog count machine and I don't want a great big count window opening in the centre of the faceplate, and secondly, well, there is no secondly, that count thing is in the wrong place, oh yes, also the PR-99 faceplate turns through 90 degrees on the top, which is not a bad thing, just of no use to me in the current setup..

So a suitable 2.5mm aluminium plate I had purchased months ago was setup on the mill and machined to as best as possible imitate a PR99 MK 2 faceplate, thankfully I still had some of the tooling I had made to cut the tension arm curvature, unfortunately the job did not come out quite as pretty as I would like, and maybe I should take a little extra care on some measurements, but come out she did...

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Interestingly the PR99 supply reel tensioner is completely different to the B77 tensioner in that it incorporates a 'damper' piston of sort, interesting too is that the 'arc' in which the tensioner arm operates is different to that of the B77, however only by a small margin, and I think it all has to do with the display electronics which share much of the same space when assembled.. This meant opening up the large round hole on the B77 chassis left, to the 'cathedral' window style hole as that is what is required to facilitate the fitting of the PR-99 supply tensioner arm..

If you are wondering why I did not just use the PR99 facia chassis you would be right, I should have, just did not want to strip things down further, and the facia was a sticky mess of molten 40 year old green pinchroller and rubber snot so I left her well alone..

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And then of course the top of the pinchroller arm had to be milled 2mm down in order to allow clearance for the takeup tension arm movement..

If you are a technical old timer with these very machines you will know that the one weakness on the pinchroller arm is the plastic dog pin (I think thats what its called) that operates the tape lifters between play and other functions, those plastic pin affairs break at the screw hole, probably because of overtightening, and when they break then the tape lift mechanism cannot operate, the pic with the circled affair shows the complete steel dogpin assembly which I had made, pretty sure this will outlast me..g.jpegm.jpegf.jpeg
 
Then moved on to measure up and machine the left and right side panel finished to 10mm thick x 30mm deep, x whatever the length was, cannot remember.. Each side piece has a 2.5mm slot machined along its full length top to bottom, 1mm from the outer edge. This slot locates the upper and lower faceplate panel.

Here you see them in place, noting that the faceplate is too tall, extending from the top because the faceplate still needs to be shortened to the correct length..

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And after about 3 hours of milling, I decided to scrap the idea and go back to the stock PR99 side panels because they are just so much easier to fit to the chassis.. go figure..h.jpeg
 
The fader board which came in the PR-99 and was not used in my previous conversion (as I never had it) and the locator board electronics..

The fader board doubles up as the tape reel size and tape dump functionality, I will not use the fader for fader functionality, just the reel size and tape dump..

The locator board image is from my previous build, just using here for visual referenceo.jpegLocator.jpeg
 
Painted black and testfit of panel, naturally I discovered that the display panel slot was about 2mm too far out of whak somewhere because the blessed display card gets caught up on the supply tensioner assembly, could not exactly move the slot over so some fine grinding adjustments was required on the PCB in order to facilitate a good fit, which thankfully worked..

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Then around 2km of wiring needing to be redone, I did not have the original wiring loom for the locator board and its respective new interfacing to the B77 electronics, but I did have a ton of scrap Revox assorted PCB plugs (connectors) so I was able to rewire these multiwire connectors to satisfy the need, albeit not to the correct Revox colours, so Goodness help whomever gets this after I am dead and gone...


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And then the crunch, typical of what happens when you work arse to face, turn on the affair and bang, fuse blows....

So I did what any respectable techie would do, fitted another fuse and watch that one blow..

That's when I know there was a real problem that was not there before.. Wiring??? Lectronics??? Milling swarf hidden somewhere???

I know I double double checked the wiring and I was not convinced that would be the issue, so started off by disconnecting all the plugs on the locator board and with fresh fuse in site turned on to no sudden flash, so its the locator board..

And then the brain does a fart... Tell me I have just spent the better part of two weeks shoving all this exercise while having a faulty locator board from the onset, yet I could have sworn I tested it, or did I..??

Clearly not...

So off comes the locator board only to be swopped into my 2nd conversion machine, and yep, just like Murphy predicted, fuse blows in the 2nd machine, so now its a 2 point proof that the locator is shot, and I'm seriously miffed...

Look closer at the 'faulty' board only to find that the main regulator transistors had been previously changed or desoldered, and only then note that someone had written E14 on the board with a permanent marker which I read as some form of error code, so I panic as one would because now I am completely convinced I bought a dud with real money and that I have no recourse..

Where does one start, its all chips and things and double sided which adds a layer of real frustration, but the simplest thing to do is measure across the locator board power and ground rail and see what comes.... beeeeeeeeeeeeeeep... Dead short....

Damn.. Check the regulator transistors - just fine, well at least I think so..

Check continuity across the main filtering cap, just because, beeeeeeeeeeeeeeeep.. dead short.... can it be...???

Removed said cap from the board and remeasured with an ounce and a half of doubt, because it never is, damn was I wrong, absolute dead short cap..

Had an identical spec replacement in the bottom of a box, banged it on the board, turned the unit back on and she sprang to life like it was 1983 again, man what an absolute relief..

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And yes, here she is now sitting on top of the pub, no audio boards installed yet but that's a quick in and out, just need to machine some give or take 20mm standoffs allowing the correct rearward placement of the rear input/ouput panel, as that is attached to the front chassis, which has been moved forward and I want this affair to fit back into the stock B77 housing.

Yes, she works beautifully, count is spot on, adjusts the time according to speed including the adjustment for position on tape if one was to change the speed setting, the auto locate works exactly as designd to do for the PR99, wonderful to see another B77 with dynamic braking and auto forward / reverse control of the spools as zero is reached or even overshot, man this looks and works just like I wanted them to when I first met Mike all those years ago, thank you Sir, you have kept me young and sane for a fair period, don't suppose you have a few more sitting about gathering dust now that I am done with all the stock I have..??😆😆

Anyway, the first pic is the unit I have detailed above, the 2nd pic is with her 'almost' identical twin I had built up some time back earlier this year..

PS - I still need to make an upper cover to match the 2 smaller original Revox side covers I used, but that is a fairly simple operation, just need to find a particular milling cutting tool I do not have just yet..

So there you have it, If you have made it this far I hope that you have enjoyed the read and till next time..

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