Resurrecting a 4-track revox b-77

[Catmanboo]

I've had this thing stored for years, have no recollection how I ended up with it. Decided to give it a go. Here's what I've found so far:
1. Belts for counter missing.
2. The 3 stud-mount oil caps (4.8.uF, 160V have all leaked out-hell of a mess inside.
3. Pause button missing.
4. Amp apparently dead, no output, all fuses good.
5. Pinch roller glazed (ok, least of the issues).
6. Left VU meter needle gone, as in no trace of it.
7. Left VU meter backlight socket crumbled, still have the bulb.
Tape transport functions apparently still good. Question of the day is- attempt to fix, or is it not economically feasible to proceed? It's a 3 3/4-7.5 ips model.
Biggest question is those 3 oil tanks that fouled the whole thing. Replaceable, or doom? Working without a schematic, don't know their function. Advice,ideas welcome!

 

[jlb2]

The main question is: how skilled are you in electronics and mechanics? All the problems you describe are fairly simple fixes, and parts are not difficult to find for a reasonable cost, but without sufficient know-how and equipment this can easily become a difficult task will little hope of success. Given the general condition you describe, you should also be prepared to change more parts (chemical and X2 caps, trimmers, ball bearings, etc.) and recalibrate the machine to bring it back to its full working condition. It's probably not worth attempting yourself, unless you consider the restoration as a hobby in itself.

As for the 3 leaking capacitors, they are phase shift caps for the motors. These are not usually the first parts to fail in a Revox so, if they are leaking, there is a high probability that other parts have failed too.

 

[Tinman]

Forget all that for the moment..... How are the HEADS??
If the heads are good, bringing a B77 back to top shape is actually very easy. LOADS of parts available everywhere.

I have put scrapped parts decks back together just because.

Now if the heads are shot..... then it may not be worth it other than a parts donor.

 

[jlb2]

Ah, the heads, I forgot to mention... In fact it's not so difficult to find heads in decent condition at a decent price around here (don't know the situation in the US though), so even a Revox with shot heads can be a good base for restoration. I've done this a couple of times with great success (i.e. back to their original specs). It takes skills and equipment to readjust everything after the head change, however. Probably not a project for a beginner.

The sign of a worn head is a flat spot (in the centre of the surface) with a width exceeding 4 mm. New or relapped heads have a cylindrical shape over all their width, with no flat spot. This thread shows pictures of Revox heads in various conditions, that you can use as a guideline.

 

[Catmanboo]

Actually, heads looked pretty good upon exam. Didn't think to take pics for proof. Main concern is the apparently non-functional amp. Mechanically, I've no fear of this thing, after digging into my teac a-2060 the last few days. Now, there's a mechanical nightmare!
Getting sound from tape to output on this one would be the goal. I'm no master tech with a lot of diagnostic gear, but can read schematics, troubleshoot via DVM, wield a soldering iron , figure out obvious issues (usually ). As for recalibration I'm sure I'm not equipped for that, so back on the shelf for now. As far as parts availability, clue me in! Thanks for all replies!

 

[jlb2]

Actually, heads looked pretty good upon exam. Didn't think to take pics for proof. Main concern is the apparently non-functional amp. Mechanically, I've no fear of this thing, after digging into my teac a-2060 the last few days. Now, there's a mechanical nightmare!
Getting sound from tape to output on this one would be the goal. I'm no master tech with a lot of diagnostic gear, but can read schematics, troubleshoot via DVM, wield a soldering iron , figure out obvious issues (usually ). As for recalibration I'm sure I'm not equipped for that, so back on the shelf for now. As far as parts availability, clue me in! Thanks for all replies!

Pratically all the parts that can go bad on a Revox are easy to find on the auction sites, including those that have failed on you (counter belts, pause buttons, pinch rollers and meters. I advise against buying used pinched rollers and capacitors though, because they are probably in bad condition and -unlike heads- it's not easy to tell from the pictures. Some ebay sellers that I've had good experience with are vew52 and revox-online, both in Germany. You might also check Nagravox in Australia. Note that the pause button is not available separately AFAIK, you will probably need to replace the whole keyboard.

Revox service centres are still around, and still sell many spare parts (notably the idler wheels and the counter belts), often less expensive than ebay sellers. Likewise, standard electronic components (capacitors, trimmers, etc.) and mechanic parts (bearings, etc.) are still made and are sold by electronic stores like Mouser, Farnell, etc. cheaper than ebay sellers.

Those 4.8 µF oil caps are a mystery. The B77 uses two 4.3 µF and one 3.5 µF MP caps. It looks like someone replaced them with unsuitable types and values at some point.

As for the play amplifiers, they are a PCB card that is easily replaceable. You can easily find one on the auction sites if you feel you cannot fix it yourself. Make sure you buy one for the correct speed and EQ configuration, since the equalisation network is located on this card.

You will need the service manual which is available on hifiengine.

I hope all this can help you.

 

[Catmanboo]

I hope all this can help you.[/QUOTE]
That's very encouraging, & I appreciate the time you invested in your reply. I'm aware of the desirability & quality of these things, hence my desire to eventually resurrect this thing from the fix-it-later pile. Once I have the time, equipment & schematic, I'm going to be all over this thing. Tnx for your input, much appreciated!