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+--- Thema: Nagra III - how to calibrate (/showthread.php?tid=33205)
Nagra III - how to calibrate - Vladislav81 - 24.06.2025
Hello, it's me again. In addition to tube Telefunken M5, I have Nagra III BH (broadcast version with 3 heads with no pilot). Now it's being repaired, replacing the belts with the new ones.
The question is how to calibrate Nagra III. I'd like to know how to do it so to tell the technician.
Hope you would help me.
RE: Nagra III - how to calibrate - bitbrain2101 - 24.06.2025
Hello Vladislav,
you can find Nagra Service Manuals at the Nagra homepage easily for download. I cant tell you more, no experience with Nagra 3, good luck.
Regards, Tobias
RE: Nagra III - how to calibrate - Magnettonmanni - 25.06.2025
Hello Vladislav,
This world is so small. We just meet again.
I have such a Nagra III too. It even still says Telefunken on the front plate.
I've had my device for 50 years and before that, it was in heavy use at a broadcasting company.
My device hasn't needed calibration yet (what exactly do you mean?)
Nagra III devices are very stable over long time.
Very important for Swiss precision devices:
Never change a running system.
But if the same mechanic tinkered with it as with your M5, I don't see much hope for the Nagra III.
By the way:
Were you able to fix the problem with the engine clutch disc on the M5 and reinstall the brakes correctly?
This is of great interest here.
This forum thrives on the questioner writing at the end to explain whether and how the problem in question was fixed.
This is the only way knowledge can be accumulated and shared.
Otherwise, the whole thing will have the quality of reading tea leaves in the long run.
I'm looking forward to your answer and then would be happy to help you again.
Best regards
Manfred
RE: Nagra III - how to calibrate - Vladislav81 - 25.06.2025
Hello, Manfred, by "calibration" I mean setting the recording level and bias that are correct for EMTEC PER 528 tape.
There is all-new pinch roller for Nagra III and there will be the belts for both take up and supply reel holders.
Answering your question. I've decided to completely revise Nagra III first because the story of M5 seems to be too long. And because Nagra is lightweight and portative tape recorder, too. Frankly, I have not got enough money to completely restore M5, because to do that I have not only to replace engine clutch disc and reinstall the brakes, but also to change all the rubber rollers including the pinch roller.
When I got my Nagra III, the tape speed 15 ips was wrong and it couldn't play back and rewind tapes. Now it can play back (in the mean of mechanics), but yet needs belts (will be here in a week or so) and it needs to be calibrated to EMTEC PER 528.
And, by the way, here in Russia almost everyone doesn't see any reason for me to have MONOphonic tube M5. Many people asks me what do I need it for, and who in XXI century needs mono recordings. When I reply "I need", they say it's silly.
There isn't too much sound culture in Russia.
Best regards
Vladislav
RE: Nagra III - how to calibrate - Magnettonmanni - 27.06.2025
Hello Vladislav,
With the Nagra, the recording level is not adjusted in the amplifier.
During recording, the Micro or the P+ control are only used for this.
The bias for tapes from 40 years ago was generally not different from your PER 528 tape.
That tape was also available back then, but in even better quality.
If you want to use a new tape on the Nagra at 38, there's really nothing better.
Because of the Nagra's low tape tension of approximately 40-50 p, the PER 368 from back then would actually be even better.
I can only advise you against interfering with the device's circuitry to somehow optimize something. It will usually only be a deterioration compared to the original Nagra specifications.
I am thinking that the Nagra plays and records at this time.
The instruction manual available for download from Nagra is actually the service manual and therefore exactly right for you.
It describes everything about repairing this little marvel from 1960 in detail.
Please first read through and internalize everything about the proposed work before proceeding.
Spare parts are scarce, and even if they are available, they are very expensive.
Your motives for choosing your recording equipment are entirely your own.
Discussing them with people who have different interests cannot lead to a mutual agreement, and it doesn't have to.
The world is big enough for all tastes.
I have three important questions:
1. Why does the rubber pressure roller on the Nagra need to be replaced?
2. Why do you need a new clutch disc on the M5?
3. Why do you need new rubber rollers and the pressure roller on the M5?
Best regards
Manfred
RE: Nagra III - how to calibrate - Vladislav81 - 28.06.2025
Hello, Manfred,
Answering your questions:
1. The rubber pressure roller on Nagra need to be replaced because the original one become unusable: it creates a lot of wow.
2. I need a new clutch disc (that is, bearing) for wind up motor for M5 because the original one become unusable, too. It causes an uneven movement of the take up spool.
3. I need new rollers for M5 because the original rubber on all of them has become too hard, and the bearings on the capstan (internal) rollers are too bad now, because they create the noise similar to the noise of Diesel engine, and it's too loud.
I have not the possibility to replace all that from nos. 2 and 3 - for now - that is why I've decided to restore Nagra III.
As for the tape choice: I've chosen to use the thick PER 528 because of the thickness of it's magnetic layer. I'll use the Nagra III for the recordings from the microphone, and it's almost impossible to foretell what would be the incoming signal level during the concert. The thicker is the magnetic layer, the greater the overload capacity of the tape. I have approx. 5 km of 528 right now, so I've decided to use this tape rather than the thinner one.
Best regards
Vladislav
RE: Nagra III - how to calibrate - Vladislav81 - 01.07.2025
Hello, Manfred,
I've forgot to tell you why am I going to reset the recording level for 528 tape. If I set the line input level to "0", set Nagra to recording mode with tape and engage 1 kHz test signal, the modulometer doesn't show "0" dB. I think it should show this value in this very case, shouldn't it?
Best regards
Vladislav
RE: Nagra III - how to calibrate - Magnettonmanni - 06.07.2025
Hello Vladislav,
It's very gratifying that you probably won't have any problems acquiring a new pinch roller for the Nagra. I couldn't just quick install a new one here.
However, over the past 40 years, I've always remembered to set the control lever to 45°. Then the rubber roller and the rewind drive belt aren't pressed and don't get pressure marks.
Film professionals would put the Nagra in standby with the rubber roller pressed down and only then quickly start it with the main switch while the cover was closed when a new take for a film section was to be recorded.
Radio reporters sometimes remembered to lift the rubber roller off the capstan after an interview. This made the rollers last longer.
The early machines didn't have any markings for this rest position. Yours might not either.
Back then, I painted the marking dots on the control knob and the chassis with nail polish.
Regarding the M5's clutch disc,
It would be interesting for me to know:
Is it bent?
Does the ball bearing have any play?
Are the friction linings worn or unevenly worn?
Is the threaded rod relatively free of play and clean?
Is the brake for the disc still good and correctly adjusted?
Now for your Nagra problem:
Using a test tape whose full-scale level should meet your requirements, you can read the value displayed by the modulometer during playback with the control set to 0 dB. This value should be memorized.
Then, during recording, feed as much input signal of the same frequency (e.g., 1000 Hz) to the device's input until you get the same reading at the output.
Then, you can remember what the modulometer displays during recording and thus know exactly up to what value you can drive without reaching an unacceptable distortion factor (over 1%).
Your idea of considering the thickness of the tape layer as an overload reserve is somewhat daring.
But everyone is the architect of their own happiness.
By following the procedure I outlined above, you'll save yourself a lot of troubleshooting, because then various components would have to be replaced. It's not as easy as with the M5, where you would have found the corresponding adjustment controls.
Soldering around in Nagra's electronics often leads to new problems with difficult errors.
It has to be done by experienced radio technicians.
This isn't a "quick fix."
Best regards
Manfred
RE: Nagra III - how to calibrate - Vladislav81 - 07.07.2025
Dear Manfred,
The pinch roller is already installed. Works great, but the recorder needs new belts, and they'll come the next week.
I understand you thought on Nagra III. One should not touch the working system, that is, shouldn't solder and replace anything electronic in this recorder.
Regarding the M5's clutch disc, I can answer neither question, because to do that I have to disassemble the winding motor, which is I'm afraid of. I think I wouldn't do it correctly and that I wouldn't be able to assemble it right.
Best regards
Vladislav
RE: Nagra III - how to calibrate - Vladislav81 - 20.07.2025
Dear Manfred,
Well, the technician has installed the belts yesterday. When working from the Nagra power supply, there's no rewind. When fully disengaging the pressure roller while in the play back mode, Nagra goes fast forward instead of rewind.
Also, I know, that while in play back mode, one can slightly take away the pinch roller from the capstan, and the transport goes into the fast forward mode. This isn't so in this particular Nagra III.
Also, even while in the Test mode, she can fast forward. So I have to engage the pinch roller first, and after that switch to the Test mode.
Other than that, my Nagra III records from the condensator mic (with it's own power supply) just fantastic at 15 ips even on ORWO TYP 106, with huge amount on low frequency, and all other frequencies are OK too. I'll not touch the sound electronics. It sounds way better than Mechlabor STM 310 (which I also have) and Telefunken M5b Stereo (which I has had).
But, it records from the line sources with buzzing. (I'll recheck it tomorrow).
UPD: The problem with the lack of rewinding turned out to be, of course, mechanical. One had to adjust the spring in the left reel holder - and here is it, the rewind and the correct tape tension in the play back and Test modes.
Best regards
Vladislav
RE: Nagra III - how to calibrate - Magnettonmanni - 22.07.2025
Dear Vladislav,
We must be careful not to get into the realm of Kudelskian psychology.
I have decades of experience with the Nagra III and don't really understand your descriptions.
Now, in small bites:
(20.07.2025, 23:33)Vladislav81 schrieb: Well, the technician has installed the belts yesterday. When working from the Nagra power supply, there's no rewind. When fully disengaging the pressure roller while in the play back mode, Nagra goes fast forward instead of rewind.
This is almost a miracle!
A rewind belt can't produce fast forward, especially since the Nagra III isn't designed for fast forward.
(20.07.2025, 23:33)Vladislav81 schrieb: Also, I know, that while in play back mode, one can slightly take away the pinch roller from the capstan, and the transport goes into the fast forward mode. This isn't so in this particular Nagra III.
Also, even while in the Test mode, she can fast forward. So I have to engage the pinch roller first, and after that switch to the Test mode.
I don't understand that.
You should make a film from the Nagra III without any modulation from the tape.
(20.07.2025, 23:33)Vladislav81 schrieb: UPD: The problem with the lack of rewinding turned out to be, of course, mechanical. One had to adjust the spring in the left reel holder - and here is it, the rewind and the correct tape tension in the play back and Test modes.
Actually, all the supposed problems could be fixed by now.
Where did you buy the belt and the rubber pressure roller?
I'm also interested in this as a spare part for my device for the next few years.
Best regards
Manfred
RE: Nagra III - how to calibrate - Vladislav81 - 22.07.2025
Dear Manfred,
Thank you so much for your message!
Now to your questions:
1. "A rewind belt can't produce fast forward". Yes, this is true. When the mechanics is working as it should, then, without the tape, in play back mode, both reels must rotate in opposite directions (left - clockwise, right - counterclockwise). Thus the tape tension is achieved. But when the technician first put the belts on, only right reel holder rotated in the play back mode, despite that there's the belt that binds the left reel holder and the motor. The left reel holder didn't rotated at all. And I didn't ask myself why, for some reason I didn't think about it. Yesterday me and the technician again put our hands on Nagra. And I drew his attention to this circumstance. He immediately started to think what is the reason of that, and soon found out that the spring that goes from the left reel holder is not tight enough to make this holder rotate in the play back and Test modes. He adjusted this spring and - voila! - it started working! Thanks God there were no electric problems in that, thanks God...
2. "I don't understand that".
When Nagra III is working, in play back mode, when the pressure roller is fully disengaged, the tape mechanism starts to REwind the tape. That is, to wind it backwards. In this mode, one can engage the pressure roller, but without pressing it against the capstan. Then the Honeywell microswitch inside engages, and the tape winds forward. This mode could be used as the "dirty" fast forward. And we can press the accelerate button to further speed it up.
In the Test mode, both reel holders rotates in opposite directions at the same speed, in order to tension the tape.
3. "Where did you buy the belt and the rubber pressure roller?"
Well, there is a little factory in Russia that produces the belts and the pressure rollers to order. But they cannot make round belts. The square belts works too.
UPDATE: Now, in July 22, Nagra III works completely. Seems to be almost impossible for Russian province in such a difficult time, but this is true. Records and plays back it's own recordings very nicely at 15 ips on ORWO TYP 106, EMTEC PER 528, and even MTP 480 tape made in Kazan factory from ORWO semi-finished products. The recording level on MTP 480 tape is lower than the input level, though, and one should be accurate with the recording level, but the sound is still clear. Meanwhile, my Nagra III is tuned to neither of these tapes. But the sound quality is very good, only slightly differently colored from tape to tape. There's no loss of high frequency on neither of the tape. I just wonder.
Best regards
Vladislav
RE: Nagra III - how to calibrate - Vladislav81 - 07.08.2025
Dear Manfred,
Yesterday I've copied some old classical music soviet recordings from 1950's from MEZ-28A to Nagra III. MEZ is a soviet studio tube monophonic tape recorder with speeds 15 and 30 ips. The original tapes (actually, the first grade copies of the original recordings) were all AGFA Wolfen TYP C at 30 ips. Nagra was recording on EMTEC PER 528 at 15 ips. The sound came through the sound path of French color TV SECAM studio system at the museum in the university in Moscow. The mixer board, as the rest system, is from 1967 and fully Germanium transistored. The sound is great, by the way.
I'd like to say that the overload capability of Nagra III on this tape at 15 ips is great. The modulometer can show above "+2", and the sound is OK.
Nagra III is great tape recorder.
Best regards
Vladislav
RE: Nagra III - how to calibrate - Vladislav81 - 13.08.2025
Dear Manfred,
And here's more than that. I've tried to record a high quality music from High-Res digital to M5 at 15 ips on EMTEC PER 528. When played back on M5, it's OK. When played back on Nagra III, the sound is somewhat wobbled, and high frequencies seem to be "chewed". When recording on Nagra III on this type of tape and then playing back on this very tape recorder, it sounds great. I don't know what is the reason. So, these recorders are incompatible?
Best regards
Vladislav
RE: Nagra III - how to calibrate - Vladislav81 - 16.09.2025
Dear Manfred,
My Nagra III participated in digitizing of the tape archive that belonged to famous Soviet viola and viola d'amour player Vadim Vasiljevitch Borisovskiy. It was decided to release these recordings on a series of CDs.
Best regards
Vladislav
RE: Nagra III - how to calibrate - Magnettonmanni - 22.09.2025
Dear Vladislav,
Please excuse me for not answering to you until now.
I have had a lot of problems with myself and the rest of the world.
I'm very pleased about that you're happy with your Nagra III.
You can probably imagine how thrilled I was when I first saw the device in 1962.
A device with all these excellent features had never existed before. When the broadcasters finally introduced this device, there was a rush of buyers that made the Kudelskii company very rich.
To your observations regarding the various audio tapes:
Agfa **PER 525 or 528 were probably the best tapes available at the time, considering all their features. They had even been designated as reference tapes by international commissons.
All reputable manufacturers of Class38-Broadcast-Tapes tried to set the optimal operating point of their tapes so that it matched the operating point of the reference tape as closely as possible. This had the advantage that you didn't have to readjust the devices for each tape.
These ** tapes can be used with excellent results on all flawless devices with 15 i/s.
I could not understand the statement "recorders are incompatible" for Magnetophon M5 and Nagra III.
Best regards
Manfred
RE: Nagra III - how to calibrate - Vladislav81 - 23.09.2025
Dear Manfred,
I totally understand you and I wish you a lot of health and luck.
I can hardly imagine what appeared to the world Nagra III back in 1962, what a revolution it was. Even with those acetate tapes, I think it was the greatest field tape recorder one could ever seen before.
I use EMTEC PER 528 with it at 15 ips, and it works great.
M5 (at it's current state) and Nagra III seem to be incompatible in sense of equalisation.
Best regards
Vladislav Semyonov
RE: Nagra III - how to calibrate - Magnettonmanni - 26.09.2025
Dear Vladislav,
I wanted to give you a tipp some time ago about how to keep the pinch roller from getting dents after 50 years of use,
and how to keep the rewind belt from wearing out or getting pressure marks.
I made these markings with nail polish.
[attachment=84720]
The toggle switch must be set to approximately 45 degrees.
Best regards
RE: Nagra III - how to calibrate - Vladislav81 - 26.09.2025
Dear Manfred,
Thank you so much for the tip! I know this, though, and on my tape recorder these black dots are installed in exactly this position from the factory. Every time I use the tape recorder, I make sure to set the knob to this position.
Also, when playing back, I always take the signal from the upper monitoring socket, and I take the ground from the appropriate recording socket on the right side.
When playing back the warped tape, I use to take the little plastic bottle and put it in between the record and play back heads so it would tension the tape on the play back head. This way, a large number of dropouts can be avoided.
Best regards
Vladislav Semyonov