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Messages - Tim

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1
Reel to Reel Tape Machines / Re: Technices RS 1520
« on: December 27, 2015, 06:42:34 PM »
Be aware that this deck does not have true IEC EQ (needed for the Tape Project tape).  The EQ switch on the front panel only changes the high frequency EQ to IEC.  The bass EQ stays at NAB, which means 50 Hz with be down 3 db.  There is a circuit mod to make bass flat (IEC)

Also be aware that you deck very likely has leaking capacitors.  Very common in this series due to age.  A full re-cap is recommended.

All pots and switches in the deck will need to be cleaned if that has not been done recently.

2
Tape Project Albums - general / Re: Compatability
« on: June 26, 2014, 12:12:07 PM »
That deck will sort-of work with TTP tapes if you use tracks 1 and 4 for playback.  S/N will not be optimum because the deck's track size is about half the size of the recorded track size.  TTP tapes played back on your deck will be somewhat nosier than normal.

Then there are EQ problems.  Your deck has 3150/50 usec play EQ.  The TTP tapes need 35 usec play EQ.  That means the TTP tapes played on your deck will have a bit more treble than normal.  If you have a tone control, you could just turn the treble down a bit. Also, played on your deck, the TTP tapes will have less bass than normal due to the 3150 EQ circuit (-3db at 50Hz). However, something called "fringing effect", may compensate somewhat for this theoretical bass loss.  Bass may be ok as a result.

3
General Discussion / Re: Head Alignment on an Otari MX5050 B2HD
« on: November 20, 2013, 03:42:00 AM »
However just looking at the heads it appears that they need an Alignment.

What exactly are you seeing that tells you the heads are not aligned?   Are you quite familiar with what perfectly align heads look like?  First thing to check is the head alignment screws....is the lockpaint broken?  Do they look like they have been turned by someone?  If they look "unturned", then they have the original factory alignment and that should not be tampered with.  Heads do not "go out of alignment" all by themselves. 

If someone unqualified has misaligned the heads, then yes, they heads will need to be realigned.  Also, if the deck has been used for a significant amount of time with misaligned heads, then the heads will be damaged and will need to be re-lapped or replaced.

As far as an alignment tape, you will only be able to adjust the azimuth with it.  A scope will be needed to do that correctly.  Adjustments like head height and head tilt (zenith) are aligned by other means.  And this assumes that, in fact, the heads actually have been adjusted out of alignment by someone.

Generally speaking, if heads have been put way out of alignment by someone (incorrect azimuth, zenith, height, wrap and penetration), only an experienced RTR technician will get them back to perfect.  On the other hand, if someone has made very minor (incorrect) adjustments to only the azimuth screws, then yes, with a test tape and scope, you can get them back to proper alignment.

4
Reel to Reel Tape Machines / Re: New Reel to Reel Player :)
« on: October 30, 2013, 05:01:39 AM »
Unfortunately, that defect likely is not repairable on that particular model. Teac used very small DC motors to drive the reel hubs (via a belt).  Those motors proved to be very under-powered and very unreliable.  Almost a 100% failure-rate. The only real fix was a mod kit (sold by Teac) which replaced those DC motors with large, direct-drive AC motors. It was a major modification to the transport which also included circuit boards for the new motors.

Teac stopped selling those repair kits decades ago, so odds for finding a NOS kit for sale on eBay will be  very low.

Sometimes a technician can "sort of" fix the original transport, but it won't last long. It's a bad design.

5
Tape Tech / Re: Revox A77 - calibration problems.
« on: September 19, 2013, 12:46:20 PM »
I've never tried to readjust the guide so that the tape contacts the guide post/brass spacer, so that may not even be possible.  Like I said, the tape does not need to contact the post and Revox did not intend tape to contact the post. Did anyone tell you the tape needs to contact the post, or is that just your assumption?

The person on Tapeheads only said he was "pretty sure" it does, which means he has not actually observed the tape contacting the guide post. It was just a guess on his part.

I would just leave the guide alone and not do anything to it.  If the factory lock paint (on both the bracket and height screw) is still intact, that means it's correct and should not be tampered with.

6
Tape Tech / Re: Revox A77 - calibration problems.
« on: September 18, 2013, 10:38:36 AM »
 Revox decided there was no need for the tape to contact the brass spacer part of the guide, so what you are observing is normal. The guide flanges will guide the tape.  You can change the guide penetration by loosening the bracket screw and moving the entire assy forward if you want (so that the tape contacts the brass spacer). That, however may change the play head tape wrap angle, so don't over do it.  Or just leave the guide alone.

When adjusting any head height, it is important to turn all three alignment screws (height, tilt and azimuth screws) by exactly the same amount.  If this is not done, the head tilt (zenith) will change from it's proper factory-aligned position.  Even small head tilt errors will cause problems (premature head wear one of them). Azimuth should be re-adjusted/re-checked after any head height adjust.

7
Tape Tech / Re: Revox A77 - Brake drum belleville washer
« on: September 11, 2013, 11:45:10 AM »
Buy the toothed counter belt from eBay.  Search "Revox belt" and you will see many purchase options.

Pulley is the white round disk that the belt threads onto.  Pulley shaft is a metal rod the pulley is attached to.  "Bearing" refers to the hole in which the metal shaft resides.

 

8
Tape Tech / Re: Revox A77 - Brake drum belleville washer
« on: September 11, 2013, 01:20:19 AM »
Who said the noise was the belt rubbing the band or hub ("friction from the belt")?  I didn't. I told you it was from the counter. 

It's not from the "counter gears" as you stated. It's counter pulley bearing chatter (due to dried up lubricant). Pull the counter pulley off it's shaft, remove the shaft.  Then cln/lube the shaft & bearing.

Any particular reason you ignored my advice (and had to be told twice what the defect was)? I carefully explained why it was not the reel hub and that it was likely the counter and yet you kept going on about your "defective brake hub". 

9
Tape Tech / Re: Revox A77 - Brake drum belleville washer
« on: September 10, 2013, 03:42:18 PM »
The noise on the video sounds exactly like the counter squealing (as I already suggested).  It's a very common problem that I have observed many times in A77 decks. During fast wind, the brake bands do not touch the brake hubs (or they should not). If the band is rubbing the hub during fast wind, you should fix that.

The brake hub material does not "wear out".  As I stated before, the original glue for the hub cloth migrates to the surface and can make the hubs sticky. That would cause other defects, however. 

Also, when you removed the brake band, did you also remove the counter belt?

 


10
Tape Tech / Re: Revox A77 - Brake drum belleville washer
« on: September 06, 2013, 03:35:17 PM »
Washer 16 is how you adjust reel table height (by removing or adding).  Changing the height by small amounts does not effect brake wear. Be aware that 7" plastic reels and 10" metal reels have different heights.  If you want to use both size reels, adjust reel table height for 7" plastic reels and then use rubber spacing pads when using 10" reels (or use an NAB adapter with a built-in spacer. Some Teac adapters have that feature)

11
Tape Tech / Re: Revox A77 - calibration problems.
« on: September 06, 2013, 11:37:43 AM »
It's not possible that bass response (20 to 1K) changes radically with typical bias levels as you claim it does.  That means your measurement methods and measurement equipment (computer-based) is likely flawed.  Only use an analog sine-tone generator and analog AC millivolt/DB meter for setting bias, EQ and levels.

http://www.newark.com/tenma/72-505/audio-signal-generator-frequency/dp/66F3575?in_merch=true&MER=ALT_N_L5_ElectricalAndElectronicTest_None

http://www.ebay.com/itm/TEST-EQUIPMENT-LEADER-LMV-181A-AC-Millivoltmeter-Wide-Bandwidth-Audio-Volt-/151115625692?pt=LH_DefaultDomain_0&hash=item232f3174dc

An addition problem (other than your inaccurate measurements) could be the condition of the heads.  They could be damaged from long-term oxide deposits (tape residue left on heads for years can cause corrosion).  They could still be dirty.  They could have been misaligned by someone and they could be worn-out.

5-6 db overbias with SM911 tape @ 7.5 ips @10K should give you a flat HF (1 and 10K the same level) after adjusting record EQ. It should also give you a good (< 3% ) distortion level at peak record level (+6 VU). Be aware that turning the bias pots CW does not always mean you are increasing bias to the record head. On some decks increase is CCW (I can't recall right now how the A77 is oriented).

 

12
Tape Tech / Re: Revox A77 - Brake drum belleville washer
« on: September 06, 2013, 10:47:17 AM »
Grinding noise during fast wind is likely not a problem with brake drum lining.  In fast-wind mode, the brake bands do not (should not) contact the drums.

-check left tape guide ball-bearing or counter as sources for noise during fast-wind .

-If you have noise only when stopping from fast wind, then you could have defective (sticky) brake drum linings.  That sometimes can be repaired by cleaning the brake bands and baking the drums. Baking can remove the stickiness of the drum lining cloth.

To answer your original question, concave side should face screw.  Both orientations will work, however. It's not critical.

13
Tape Tech / Re: Revox A77 - calibration problems.
« on: August 29, 2013, 12:00:25 PM »
The A77 left channel is infamous for having not enough HF signal.  This is because one can't easily see the left track area of the head (play and record) on that particular deck and that means that oxide deposits often are left on the head surface after cleaning. I see it all the time in my repair business. Clean you heads again making sure the left track area (top area) is spotless. Use a dental mirror to inspect, or better, remove the headblock for better visual and cleaning access (3 screws).

14
Reel to Reel Tape Machines / Re: Technics 1520 motor help
« on: August 20, 2013, 10:30:42 AM »
That should work.

Also re-install that .22uf cap you removed.  .22 is the correct value.

15
Reel to Reel Tape Machines / Re: Technics 1520 motor help
« on: August 20, 2013, 09:34:31 AM »
I have two Technics motors in my shop, but they belong to customer units. No spares.


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