Telling the difference between 2-track and 4-track Revox G36??

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Urskov

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Hi there

I recently snatched 2 Revox G36 for dirt cheap. The former owner said one was a 2-track and the other a 4-track, but here's the problem... I want to keep and restore only one, whatever is the best sounding (according to another thread I posted sometime ago the 2-track is supposed to be...), and sell the other...

Here's the awkward, slightly embarassing thing: I'm completely new to R2R machines and I can't tell the difference. They both have "Stereo mod g36" written on them, both have only two VU's with "channel1" and "channel 2".

Here are the pics:
Machine 1
Machine 2

1:
2:



Is there something I am missing or is the former owner wrong?
 

PermO

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I don't know, but these look the same to me (and the same as mine).

If one was a 4 track you should be able to see a difference at the tapeheads.

Pull the triangular plastic cover from the machines and see what's underneath, if they are the same they must be both stereo machines.

edit;

Also check the track selector switches on the right.
3 settings let you choose between I or II or I +II, in case of a four track there should be more options like III and IV
 

analogguru

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The difference is in the tapehead track width:
In HiFi-applications people used 1/4 track so that at the end of the tape they could turn the tape around and the music R/P could continue without rewinding. Another benefit: double playtime. But the performance was not as good as with 1/2-track which was normally used in the studio. Another difference could be the tape speed: HiFi-machines used 9,5cm + 19cm/sec, while studio machines used 19 + 38 cm/sec as tape speed.
 

abbey road d enfer

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There should be no difference in switching between a "4 track" and a "2track".
The 4 track version has the same number of channels (two) but their position on the tape allows operation in both directions by reversing the tape. Done for economy. Twice the recording time for the same tape. It comes with some inconvenience though, like S/N ratio degradde by about 4 dB, X-talk from tracks recorded in reverse direction, less stable performance because tape drift effects are doubled.
In terms of performance there is no hesitation, the 2-track is the superior version.
Look at the heads (see attachment)
Anyway, operating a R2R machine in the 2020's is an expensive option compared to recording on a pile of sand (silicon), so you'd better choose the one that works best.
 

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PermO

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You don't have to choose, apply when you have the urge to...

I always run my mix parallel into the DAW when I record it to tape.
Then play the tape and record that in the DAW as well.

You can also use the internal tube amp and speaker to reamp a synth, stick a mic in front of it, quite nice !

It's a very usefull device, and kept in good condition these machines sound amazing !
 

abbey road d enfer

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You don't have to choose, apply when you have the urge to...
That is not the question the OP is asking. He wants to make the choice between one or the other format.
I always run my mix parallel into the DAW when I record it to tape.
Then play the tape and record that in the DAW as well.
This is using tape as an effect. I'm not sure the OP wants to do that. Anyway, it it's what he wants to do, IMO he should choose the 2TK format that will result in better S/N and signal stability.
 
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Winston OBoogie

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I think high speed (15ips) G36's are really quite rare so the chances are that both the machines will likely be the same in that regard with 7.5ips as the highest speed.
As for 2 track vs 4 track, obviously the 2 track would be the best quality all other things being equal.
Looking at the heads will tell you which is which.

With that said, do you absolutely have to get rid of one? Keeping both machines might be good from the standpoint of assembling a good one from the best parts, or having another machine around for spares etc.
Or buying a set of new 2 track heads which could go on the 4 track.

They both look like they've had a fairly easy life and not been beaten to death, but spares for a G36 are not as easy to get as they are for an A77.
 

PermO

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Yup, I would defenitely keep the other one for spare parts, a friend of mine sold his and everytime he sees mine he tells me he regrets that.

Good ones are becomming pretty rare, I was really lucky to get mine from the first owner.
 

Winston OBoogie

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For sure.

I just looked in the service manual and, besides looking at the heads, seems you can identify whether a machine is 2 or 4 track by the following markings:

"The G 36 model is available in both 2 and 4 track versions. Identification is made by the appropriate number being stamped on the head mounting plate, and on the upper side of the lower chassis."

The service manual will be needed anyway for all those caps, selenium rectifiers etc. that you'll need to replace, for help in removing the motors to rebuild and oil etc. It's online here:

 

abbey road d enfer

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The proper way to refer to these decks is half track and quarter track. Four track means that the deck can record and playback four tracks at a time. These decks are two track decks whether they are half track or quarter track in that they can only record and playback two tracks at a time.
Correct. That's why I put quotes around 2TK and 4TK. I should have been more explicit. Thanks for correcting us.
 

Winston OBoogie

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The proper way to refer to these decks is half track and quarter track.

Guilty as charged! And I didn't even put quotation marks around 2TK & 4TK.
My only defence is that I used the same terms as written in the service manual.
But you are 100% correct. Thanks Paul.
 

Winston OBoogie

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Here's an article from the very first issue of Glass Audio in 1988. It has a few useful tips on maintaining the G36 machine.

One caveat with the article is that I don't think it's quite correct regarding converting a machine to high speed (7.5 IPS & 15 IPS).
You do need to change the capstan's size as stated, but the HS modification also requires that the motor be repositioned by a couple+ of mm to ensure the machine has the correct tape path.

Anyway, plenty of sites online (tapeheads for one) where you'll find folks who've maintained and modified these.

Have fun :)
 

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  • GreeningTheRevoxG36.pdf
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abbey road d enfer

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One very important format is missing here: the "butterfly" IEC stereo head. Instead of the NAB 2mm (75 mils) track, it has 2.75mm (110 mils) width, which results in more than 3dB noise and stability improvement, at the cost of increased X-talk, which made them unsuitable for "2-track" material (remember that 2-channel tape recorders were originally used as 2-track multitrack machines, where the material on one channel bear little resemblance to the other (typically orchestra on one channel and vocals on the other).
When stereo became a viable medium, the IEC advocated the use of larger tracks with a smaller gap (IIRC 30 mils/0.75mm).
Since the Ampex document is dated 1975, it is quite surprizing they don't mention it.
OTOH, the IEC produced revision of the standard until 1988, 3 years after Sound Designer put the first nails in the coffin of tape recording...
 
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Tubetec

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Compared to most other domestic tube era tape decks the G36 is arms and legs ahead . It even has a proper valve regulated HT supply which you normally only saw in pro level decks back in the day . If these machines have had an easy life I wouldnt go mad replacing everything and anything just because you can . First go over the machine , replace anything that has obviously gone bad . Willi Studer used the best components he could back then and the vast majority of these will still be in good condition , including Elco's (electrolytics) . Fortunately also Studer/Revox service documents are beautifully written and easy to follow . Well worth keeping the second 1/4 track machine also , it may be a relatively simple job to get the first machine up and running with new off the shelf parts so avoid using the second machine as a donor if you can and you could well end up with two fully working units in the end .
 

Tubetec

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Regarding Butterfly heads , I dont think they were normally an option on the G36/A77/B77 machines , then again its always a possibility a third party might have done a conversion . Studer B67 was the only machine I ever saw with butterfly , as far as I remember the much later Otari MTR12 had the standard NAB guard band width .
 

Winston OBoogie

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Normally I'd say that machines don't necessarily need a full re-cap. But if the G36 is anything like the subsequent A77 in terms of components used, then a re-cap of some sort is strongly advised. Some of those old Rifa caps have been known to catch fire as they fail.
Best case is it'll make a lot of smoke when it does fail. And it will.


Here's what a failed Rifa cap looks so you know what to look for. Most of 'em crack.
 

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