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Revox B77 Reel-to-Reel

electrically - these machines are super easy to work on. i've done three PR99's so far ... feel free to ask if you have any questions. those heads look very good to me - i'd say no more than 20% wear as opposed to fifty ...
 
not everyone will agree with me but sewing machine oil is virtually identical - at least in function
That thought had crossed my mind but I daren't mention it.

electrically - these machines are super easy to work on. i've done three PR99's so far ... feel free to ask if you have any questions. those heads look very good to me - i'd say no more than 20% wear as opposed to fifty ...

I tried measuring the width of the flat spot with a transparent ruler but couldn't get it near enough for an accurate measurement, however I reckon it's about 3mm give or take. Some say performance begins to degrade when wear gets beyond 1mm, others say it's fine with 4mm or even 5mm of wear, - so much for consensus! :D
 
That thought had crossed my mind but I daren't mention it.



I tried measuring the width of the flat spot with a transparent ruler but couldn't get it near enough for an accurate measurement, however I reckon it's about 3mm give or take. Some say performance begins to degrade when wear gets beyond 1mm, others say it's fine with 4mm or even 5mm of wear, - so much for consensus! :D


depends on whether it's in fact 'flat' or not - if not it may not be so worn - i might go over it with a polishing wheel on a dremel or foredom (or the like) rotary tool and see how it cleans up ... better to assess once it's gone over a bit. i've seen 'flats' about the width of what you have shown that appear to be much worse than yours (from what i can tell). let me go out on a limb and predict yours will look near new once you've given them a bit of a 'clean up'
 
THIS one is quite a bit more worn than yours (and in a similar way - rounded wear, conforming to head shape, like yours) but this one could probably also 'clean up well' with a quick polish and not even need a lap ... possibly

https://reverb.com/item/6583367-rev...MI9q-88ZiI6wIV8R-tBh035QuqEAQYASABEgJjE_D_BwE
The wear guide at the top and bottom of the head is the clear indicator of flat or rounded wear. IMO on this head the wear is flat and and is the same width and depth as the wear guide, the head gaps are opening as well so for me that head is toast.
Totoman your heads are approx the same as every deck I have worked on and will calibrate up fine
If you cant get the last few marks out with Acetone you can try some polishing compound (Peak or Autosol) on a strip of microfiber cloth
I wouldn't touch a head with a demmel either If a head needs re-lapping, send it to Terry at Summertone, its actually not expensive
http://www.summertone.com/services/


Alan
 
Below is a couple of pictures of a heads with what appears to have wide wear in the first picture but as you can see the the middle of the head is still well clear of the bottom of the wear grove, so in this instance the wear was rounded. The second picture is after cleaning and polishing, they look like new

Head 1 by Alan Towell, on Flickr
Head 2 by Alan Towell, on Flickr

Alan
 
The wear guide at the top and bottom of the head is the clear indicator of flat or rounded wear. IMO on this head the wear is flat and and is the same width and depth as the wear guide, the head gaps are opening as well so for me that head is toast.
Totoman your heads are approx the same as every deck I have worked on and will calibrate up fine
If you cant get the last few marks out with Acetone you can try some polishing compound (Peak or Autosol) on a strip of microfiber cloth
I wouldn't touch a head with a demmel either If a head needs re-lapping, send it to Terry at Summertone, its actually not expensive
http://www.summertone.com/services/


Alan


hmmm - didn't see the same thing i guess - if you look closely you can see a shadow projected by the 'worn' head surface into the relief channel (what you call the wear guide i guess) ... i did not mean a dremel with a GRINDING wheel in case that's what you thought - but rather a soft felt attachment for polishing
 
Johnathan
I dont see what you are seeing but IMO that tape head is completely shot, the head gap is clearly visible in the play area so the head is at the end of its useful life ?.
The slots cut at the top and bottom of revox heads has 2 functions
1. As an indicator of the maximum wear
2. As a relief so as the tape head wears you don't have a step up which the tape could ride up onto at the edge and cause loss of contact.
Alan
 
If you look at the most enlarged picture (the last one) you can clearly see a shadow indicating there is at least 1.5-2 mm thickness of ‘worn’ area left ... I dunno ... I could be wrong but I’d like to see other pictures ...
 
Below is a couple of pictures of a heads with what appears to have wide wear in the first picture but as you can see the the middle of the head is still well clear of the bottom of the wear grove, so in this instance the wear was rounded. The second picture is after cleaning and polishing, they look like new

Head 1 by Alan Towell, on Flickr
Head 2 by Alan Towell, on Flickr

Alan
Yes that’s how I’m seeing the aforementioned heads that were posted ... (shrugs)
 
This is the best I can manage when it comes to photographs (click to enlarge). The heads don't look quite as spotlessly clean or rounded as Alan's example, but they still have decent curvature and from what I can see sit well above the wear guide. Are my cleaning duties complete?

50229040711_4ebf1437eb_o.jpg


50229040616_5027135c52_o.jpg


50229260067_64bf6aa541_o.jpg
 
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i would have no qualms using those as-is personally - and they will be quite lappable down the road i'd think ...
 
They look 100% cleaner than before and as I said previously they will calibrate up no problem
The wear pattern is very uniform and you have good clearance on the wear groves.
A flat spot doesn't actually give you less tape contact in fact it can actually give you more, with good tape tension so there should be no problem getting 30hz - 20Khz
The heads on my B77 4 track have a similar amount of wear and are just fine, see frequency response check after calibration
Alan
 
OK, so next stage is trying to workout how to measure the deck's frequency response as I have no external analogue measurement devices. I'm presuming it cannot be done with a basic DVM, so I'm currently looking into creating a 'tape loop' with my computer with an external soundcard with DAC/ADC and using software like REW or Audacity.

http://www.tapeheads.net/showthread.php?t=30669
 
I guess you could use Audacity’s frequency analysis or whatever its called to look at some Audacity generated white and pink noise, then record it to tape and back into Audacity and see if it looked much the same. Not a proper calibration method by any stretch, but it should tell you if there is much loss above your hearing range. Again this won’t tell you about the head condition (which now looks fine to me), only about the overall performance and calibration of the tape deck as a whole, e.g. it will likely be more about electronic calibration to tape type as the heads.

PS If it is a nice tidy example I’d actually be inclined to get it properly serviced.
 
I guess you could use Audacity’s frequency analysis or whatever its called to look at some Audacity generated white and pink noise, then record it to tape and back into Audacity and see if it looked much the same. Not a proper calibration method by any stretch, but it should tell you if there is much loss above your hearing range. Again this won’t tell you about the head condition (which now looks fine to me), only about the overall performance and calibration of the tape deck as a whole, e.g. it will likely be more about electronic calibration to tape type as the heads.

PS If it is a nice tidy example I’d actually be inclined to get it properly serviced.

This is my ultimate intention, however logistics are proving a bit of a challenge as my dad isn't able to drive long distances and I wouldn't like to entrust the deck to a courier. In the meantime I'm keen to get an idea of its current operational condition and whether I can get a bit of use out of it.

PS - Maybe I'll put up a request for a PFM taxi?!
 
@337alant, since my knowledge of capacitors is limited to a few types used in vintage loudspeakers, I'd be grateful for a recommendation on a replacement for the Rifa X2 that's across the power supply. A link to where I can order it from would be even better. :)
 
From a safety POV does it matter which orientation the power cable is inserted? It appears to fit both ways and there's nothing to indicate which one is correct? I've inserted it so that the cable is travelling across the fuse holder.
 


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