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Vintage Tape (Audio), Cassette, Wire and Magnetic Disc Recorders and Players Open-reel tape recorders, cassette recorders, 8-track players etc.

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Old 26th Oct 2020, 5:11 pm   #1
AdamOfBremen
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Default Help with Tandberg Model 15 2 Track

Hi to all forum members.

I have just purchased a Tandberg Model 15 on Ebay for use in my home studio. I will need to service the machine of course, and perhaps I need to replace some caps. I am good with a soldering iron but have no idea really except I have built some very simple circuits like passive mixers and the like.

Perhaps there are members with an interest in these machines? If so, I would welcome some help in an emergency as I get this thing up and going.

I picked a relatively newish model in favour of the earlier stuff, and a simple one at that, as I am only learning. It is in good cosmetic looking condition, unmarked, which I hope is a good sign it isn't worn out, though of course it is rather old.

One question I have right now is about matching to the microphone input. I see this is 200 ohm. The microphone I am most interested in getting is a Ribbon Mic rated at 260 ohm. Is his a good match or is the mic too high? I read it needs to be the same or lower, though by how much I am unsure. There are other mics available at 150 ohm but these are not ribbon mics. A standard SM58 is 300 ohm (to give an idea of relative ohms).

I was hoping to go direct into the mic input yet I also have a mixing desk which I could use as a front end and send that into the line input. That has 2,500 ohm inputs. It's just that, I was hoping to use the Tandberg as a pre-amp because the mic is relatively low output.

What do you think is best?

When the machine arrives I will take it apart to clean and lubricate it and I am sure I will have other questions by then.

Thanks and regards
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Old 26th Oct 2020, 5:44 pm   #2
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Default Re: Help with Tandberg Model 15 2 Track

Where are you seeing the 200 ohm reference, in the Instruction manual I guess, in the Service manual it also shows 200 Ohm on the schematic, but additionally under Technical Specifications it also states "For dynamic microphones with impedance less than 600 Ohm".

David
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Old 26th Oct 2020, 6:42 pm   #3
AdamOfBremen
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Default Re: Help with Tandberg Model 15 2 Track

Yes, I read it in the instruction manual (the 200 ohms bit).

Your post helped me find the service manual, which was hiding under 14-15 rather than 15 on the website. What a great manual - thanks for that. I will certainly need it, and it looks like the input is good for any low impedance microphone. I will try it and see once I have the unit operational. It gives me a little more confidence to purchase the ribbon mic now I know it should be ok.

Of interest to others, whilst researching this I found out that the earlier models were only for high impedance microphones - which would be a bit disappointing for anyone buying one of these for use as a pre-amp, which I was hoping for. It put me off the valve models in favour of this solid state version as more suited to my needs, and hopefully easier for me to maintain.

I enclose a photo for identification purposes. I would be interested in finding out the year it was made - perhaps there are some differences over the years?
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Old 26th Oct 2020, 8:37 pm   #4
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Default Re: Help with Tandberg Model 15 2 Track

According to hifiengine, Production run for the Series 15 was 1968- 1974.
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Old 26th Oct 2020, 10:01 pm   #5
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Default Re: Help with Tandberg Model 15 2 Track

Useful Tandberg catalogue including the Series 15.
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Old 26th Oct 2020, 10:26 pm   #6
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Default Re: Help with Tandberg Model 15 2 Track

You can use most mics with these. I have used the 200 ohm ones and also the 600 ohm types without problems. Just adjust the mic level.

Note that the mic signal (in Rec or Amp mode) does not feed into the preamp outputl! So forget using the Tandberg as a mic amp. You'd have to use the speaker output I suppose, which would add a little more noise to the signal.

If you connect the 'Pre amp' phono socket to 'P. Up' and put the unit into 'AMP' you can mix a pre recorded tape with the 'live' mic, and accompany yourself - not sure if that'd be useful to you.

We have discussed these machines many times over the years. They were mostly used in education, and actually in production well into the 1980s - the later black ones bearing a TED sticker. I revived one last year.

Yours seems to be one of the earliest ones. You have the two track (half track) version. Note that in all these Tandberg 15s the rec/pb head is always stereo, the upper track is fed to the Free HD socket. You can connect this to a mic amplifier to play back the other side of the tape but you can only record in one direction at a time. So no overdubbing (you can do this on the 4 track/quarter track 15-41).

The main problem on these is the Rec/Amp switch which goes intermittent and crackly. I usually clean these with a q tip and rub the contacts with switch cleaner. just spraying rarely works for long.

Gummy grease on the linkages and joystick is another problem. I could write a book about all the work that needs doing on the really bad cases! If yours has been regularly used this should not be a problem.
I have a local industrial source for the drive belts for these. The originals tend to crack and fall apart. With a good belt the fast wind is very fast!
Fitting the belt is easy but there's a lot of dismantling needed of the top deck (knobs, head cover mounts, etc).
I have never needed to replace an electrolytic capacitor in these, but there is a Rifa one across the motor switch contacts on the transformer that should be changed before it shorts out!

The 24v VU meter bulb forms part of the oscillator and if it is blown you will get horrible interference.

Of all the mono units of the late 60s-early 70s,these are the most flexible and dependable. I have about half a dozen! Got one playing into the PC as we type.
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Old 27th Oct 2020, 12:15 am   #7
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Default Re: Help with Tandberg Model 15 2 Track

Quote:
Originally Posted by ben View Post

The 24v VU meter bulb forms part of the oscillator...
Why would they do that?

Mike
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Old 27th Oct 2020, 12:51 am   #8
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Default Re: Help with Tandberg Model 15 2 Track

The rec /amp switch lifts the earth from the oscillator.

I was told years ago that the presence of the bulb affects the supply to the oscillator. You can see on the cct diagram how the bulb connects.
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Old 27th Oct 2020, 10:36 am   #9
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Default Re: Help with Tandberg Model 15 2 Track

The bulb in question is connected across the main supply when Rec. is selected.

When Pb or Amp is selected the supply to the playback booster amplifier stage is via the bulb, so far as I can make out.

Lawrence.
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Old 27th Oct 2020, 12:04 pm   #10
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Default Re: Help with Tandberg Model 15 2 Track

Quote:
Originally Posted by AdamOfBremen View Post
...One question I have right now is about matching to the microphone input. I see this is 200 ohm. The microphone I am most interested in getting is a Ribbon Mic rated at 260 ohm. Is his a good match or is the mic too high? I read it needs to be the same or lower, though by how much I am unsure. There are other mics available at 150 ohm but these are not ribbon mics. A standard SM58 is 300 ohm (to give an idea of relative ohms).

I was hoping to go direct into the mic input yet I also have a mixing desk which I could use as a front end and send that into the line input. That has 2,500 ohm inputs. It's just that, I was hoping to use the Tandberg as a pre-amp because the mic is relatively low output...
Ribbon mics, but especially older ones tend to have low output and so preamp choice can be crucial. Preamp noise which is not a problem with other mics can be so with a ribbon as source. Modern ribbons thankfully tend to have more output due I think to more powerful magnets.

These days there is usually no direct "matching" of the mic's impedance to the preamp's input impedance. Normally the actual input impedance of the preamp needs to be at least ten times that of the microphone or source.

You will usually be limited by the noise in the "mic and first preamp" combination. A second preamp normally just adds more gain but cant improve on the signal to noise ratio it receives.

If you want top performance from your ribbon mic you might be better off feeding it into a dedicated low noise preamp.

Ribbon mics can work very nicely but are fragile. The ribbon is easily damaged. It's even inadvisable to store the mic with the ribbon lying horizontally as over time the ribbon stretches and sags, degrading the output. Magnetic filings finding their way into the transducer element can also play havoc. Historically, ribbon mics were used as a higher fi mic than dynamics and before good affordable condenser mics came on the scene. The ribbon's natural figure 8 pattern can sometimes be an advantage but the most commonly useful recording mic has some sort of cardioid pattern.
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Old 27th Oct 2020, 12:10 pm   #11
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Default Re: Help with Tandberg Model 15 2 Track

Yep..... it took months for me to work that one out... but the machine was a fantastic unit.
Eventually I had a losing battle to keep it running as the PCB's just seemed to rot away...
I now have a beautiful Series 4000x.
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Old 27th Oct 2020, 12:40 pm   #12
AdamOfBremen
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Default Re: Help with Tandberg Model 15 2 Track

Quote:
Originally Posted by ben View Post
Note that the mic signal (in Rec or Amp mode) does not feed into the preamp outputl! So forget using the Tandberg as a mic amp. You'd have to use the speaker output I suppose, which would add a little more noise to the signal.

If you connect the 'Pre amp' phono socket to 'P. Up' and put the unit into 'AMP' you can mix a pre recorded tape with the 'live' mic, and accompany yourself - not sure if that'd be useful to you.
Thanks for all the good information, Ben, I'll follow your list when the machine arrives. I've been reading through the forum and studying what I find. Very useful.

Now, it is a bit of a disappointment regarding the pre-amp out. How I was going to connect the deck to my system was to go pre-amp out into a channel on the mixer, so I get to use all of the good stuff there like eq and effects sends, then I was going to dedicate the Aux send on the mixer to go to the record (P.Up) on the tape deck. My computer is connected running Audacity, to give you the full picture. So I should be able to go from the computer to the tape (ie: YouTube Jazz recordings in HD) and from the tape via the control room outs on the mixer to my stereo amp, driving my headphones and speakers. Let me know if you see any problems with this. One advantage of this is it converts the signals from mono to stereo and vice versa.

I have ordered some plugs and a cable to make up a converter to go from xlr plug on my mic cable to 5 pin din on the deck. This way I should be able to sing vocals direct onto the tape whilst monitoring the backup track playback coming from Audacity and either mix the two together onto the tape or transfer the vocal track to Audacity later and sync it up with the mouse I can also compare the result to the alternative running the mic into the mixer and going via the P.Up in and see which is better balanced to the ribbon mic.

Let me know if you think of any snags with this or any better ideas. There is an Aux send on every channel of the desk, so it should be pretty flexible as to what gets recorded mixed with whatever.

My speakers arrived today so I am preparing a place for those to go on the wall. It's a busy time getting things ready. The Tandberg looks like it will take up a lot of space and I have so little. How do these things run if you mount them vertically on the wall - would that even work?

Thanks again for your help.
(sorry I messed up the quote - i'm just learning)
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Old 27th Oct 2020, 12:57 pm   #13
AdamOfBremen
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Default Re: Help with Tandberg Model 15 2 Track

Thanks for that, very useful information. The ribbon microphone I have ordered is a new one from a well known international supplier. It's a T bone RB800. I had the idea to make my own, they are quite easy to make, then I found this one for 88, case and everything. My idea is to keep it forever and to maintain the ribbon inside the mic - it is quite easy to remake this part oneself with a few special tools.

Most of the great recordings of the 1950s were made using ribbon microphones. Some of those recordings, on CD, in my small collection, are the best sounding ones I have. This, together with listening to youtube demos, has led me to choosing this path. I already have a couple of low cost large diaphragm condenser microphones that I am not so enamoured with. I'm hoping to get more bass response and warmer vocals using the ribbon. It won't have an alnico magnet, yet the demos sound promising.

If the tape input doesn't work too good, I will put it through my mixer which has fairly clean low noise preamps. I just thought it might balance perfectly with the tape being closer to the vintage, so to speak. It's worth a try.
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Old 27th Oct 2020, 1:02 pm   #14
AdamOfBremen
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Default Re: Help with Tandberg Model 15 2 Track

One thing I was wondering regarding the Tandberg 15 - what kind of tapes should I get to suit this specific deck for optimal quality and to avoid any problematic brands? I'm going to be recording only at the high speed and will probably be using the tape over and over - is that recommended? how many times? I need to buy some off ebay this week. Maybe someone wants to sell some? I don't need many, maybe four would be good.

Thanks to all for your help.
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Old 27th Oct 2020, 2:01 pm   #15
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Default Re: Help with Tandberg Model 15 2 Track

Re: tape. There was a production change. After serial number 251 5502 the bias is set up for LH tape. Lower numbers use standard tape. That means things like EMItape 88/99, BASF LGS, the Philips in the red cardboard cartons, etc.

I can't help thinking that you're complicating matters a bit by using this machine for what you propose. These were never studio machines and nobody would have used them as such back in the days of analogue. There is very little it can offer you in this setup that some DAW plugins and a standalone mic preamp cannot give.

Of course, they are great fun and you may well find you get bitten by the bug and want more!
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Old 28th Oct 2020, 12:22 am   #16
AdamOfBremen
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Default Re: Help with Tandberg Model 15 2 Track

Hi Ben

Thanks for the advice. I am a retired guy and only doing my recording to please myself. At the moment I don't have any tape recorder at all and if I want to record anything I have to use the computer. I spent my whole life working on computers and now with the covid around I even have to do my shopping by computer! - I am starting to get rsi again

So I thought to simplify my life a bit and be able to just get up and make a quick recording on a tape that is always available if I wake up in the early hours of the morning with an idea in my head and just put that down without needing to turn on computers.

I suppose, from there other ideas emerged. My previous effort at recording were all very much stereo approaches - even my guitars were wired for stereo and split front and back pickups. I left my studio and all my equipment except my little mixer in Germany and I am now just setting up again in the UK. Now everything in the studio seems to be mono, guitars as well.

So I am going to pursue this mono idea - maybe even make mono finished tracks, I don't know yet. I am also all analogue into my computer ... which is very interesting, because I don't know anyone else doing that. Most non-computer people might think that was unprofessional, yet it is quite the opposite if one understands the limitations of USB and budget audio interfaces.

I have my computer OS set up to run it's sound subsystem at 24bit 96khz and I plug the analogue mixer directly into the analogue sound input jack. The noise floor is pretty much zero - as good as USB. The advantage this gives is that the recording levels are analogue not digital, and the problem of distorting the level in the digital domain is eliminated. This really helped in getting a good sound into the computer reliably and since I have been using this setup I would definitely not wish to go back to USB.

As I am using Linux, the USB subsystem is also not 100% yet because of USB 3 and beyond - things take time in the free software space.

So I am already analogue mostly, and it's easy for me to feed the same source to either the computer or the Tandberg - it's just a choice and then try it out, see how it sounds.

I have lots to learn and perhaps the Tandberg may not be good enough eventually. I have a limited budget and I managed to pick this up at a very good price, so it gets me started.

Having said that, if the machine is working to spec then I would be most surprised if it cannot deliver a vocal track into a mix of say six other digital tracks without degrading the result to unacceptable levels. We will see in practice. What I liked about the Tandberg was the ergonomics of it and the build quality, also the use of metal parts rather than plastic in some places. I was looking at stereo machines yet I am now glad I ended up with the mono version - it is so much simpler on the (human) head and the number of cables and channels involved.

Thanks for your help.

Regards
Adam
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Old 28th Oct 2020, 5:55 am   #17
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Default Re: Help with Tandberg Model 15 2 Track

Quote:
Originally Posted by AdamOfBremen View Post
I would be interested in finding out the year it was made - perhaps there are some differences over the years?
If you want to find out the exact production date, there should be a sticker on the mains transformer, on the side facing the joystick, so not always obvious to spot first time around. It will have a two-digit year and week printed on it. Any production changes noted in the service manual will refer to the serial number on the back though.

Apart from the change to LH tape (originally I believe indicated by a sticker on one of the reel holders saying "Adjusted for Low Noise tape" or something to that effect) I don't think there were many changes made during the course of production. However, at some point I think they revised the materials used for the rec/pb switch and after that it became a lot less prone to becoming scratchy. I have a 1983 model (like Ben was referring to) in a black plastic case which has this.

One interior cosmetic difference at some point (mid 1970s?) was the change from nickel plated (?) steel to chrome passivation, so the color of all internal metal parts changed from silver-y to gold-ish.
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Old 29th Oct 2020, 3:36 pm   #18
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Default Re: Help with Tandberg Model 15 2 Track

Well, the Tandberg 15 finally arrived - a smaller package than I expected, which is really good for the space in my studio. I took it apart and cleaned it up inside, did a little bit of careful lubrication and worked in some contact cleaner into the switches. All seems to be good to give it a go on the power.

The machine came without plug so I need to source that, otherwise I might have been tempted to try it too soon. The fuse isn't blown, which is a good sign, and all in all it seems to have hardly been used. I tried turning it by hand through the various settings and it seems to do what it's supposed to do with belts and things.

I leave a photo for your interest.

Build date seems to be 1968 from the transformer, week 22.
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Old 29th Oct 2020, 5:41 pm   #19
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Default Re: Help with Tandberg Model 15 2 Track

Since you have it open, do yourself a favour and get rid of that Rifa cap on the transformer tag strip, across the two leads going to the motor switch. You can replace it with a 0.1uF x2 capacitor rated at 400v in series with a 47R resistor. These components cost pence and will save you the horrible bang and smoke that will come about, trust me, if this is not done!
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Old 29th Oct 2020, 6:05 pm   #20
AdamOfBremen
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Default Re: Help with Tandberg Model 15 2 Track

Hi Ben

Is this the rifa cap? (see photo)

I did plug it in and spent an hour scratching my head until I found out that the tape reels need to be installed before the motor will work - guess all newbies do that.

Now I managed to run it up and down a bit. I noticed that the speed change switch was working when I first opened it and now the pin has fallen out like they all do. I will probably just jam it in place at the higher tape speed - I presume that is all the way down?

Rewind and fast forward go perfectly and the brakes work good. Play functions but is noisy. I wonder if the flywheel bearing needs lubricating? I believe this is a pig to get off. Is there a quick and easy short cut to this?

Thanks.
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