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-   -   How to align tape and set bias for Revox G36 in plain English, please! (https://www.diyaudio.com/forums/analogue-source/187344-align-tape-set-bias-revox-g36-plain-english-please.html)

Salli 19th April 2011 04:05 AM

How to align tape and set bias for Revox G36 in plain English, please!
 
Hello, Our old Revox G36 is still going strong except for one thing - it doesn't sound like it's set up for RMG 911 (like Ampex 456). Everything recorded sounds very treble, there's a real excess of high frequencies. We've never adjusted anything inside the machine and we're guessing it's setup for 60s tape rather than someting like Ampex 456? Looked at the service manual but didn't really understand it. We don't have any test equipment, just a laptop, a mixing desk and three reels of RMG 911 tape. Can anyone please help? Many thanks in advance!

rrrremus 19th April 2011 07:37 AM

I wouldn't touch the tape alignment and bias without doing some measurements first. This is an old machine and it is very likely for this problem to be caused by the aged electronics inside, like dried out capacitors.
You need a scope and signal generator in order to restore this machine.
Perform mechanical alignments only after you know that the electronics are fine.

barrymagrec 19th April 2011 08:42 AM

Quote:

Originally Posted by rrrremus (https://www.diyaudio.com/forums/analogue-source/187344-align-tape-set-bias-revox-g36-plain-english-please-post2543350.html#post2543350)
I wouldn't touch the tape alignment and bias without doing some measurements first. This is an old machine and it is very likely for this problem to be caused by the aged electronics inside, like dried out capacitors.
You need a scope and signal generator in order to restore this machine.
Perform mechanical alignments only after you know that the electronics are fine.

I would strongly agree. Alignment of a tape machine involves first checking the replay side with a calibrated test tape. Only then do you know what you are adjusting the record side to.
Don`t be tempted to twiddle things just to see what happens!
Things you can do - check the heads are clean and the tape is running correctly past them - probably not a problem as you have plenty of treble. Find an old recorded tape that used to sound O.K. If it now sounds poor the problem is most likely in the replay . A power supply problem could cause problems on play and record (old caps - see above). Lack of bass can be low emission valves or in extreme cases, worn heads, it can also be a number of other things (Is it on bothchannels?)
As a general rule using new tape on a machine set up for older types will not be optimum but will not sound really bad.

Barry

kevinkr 19th April 2011 06:01 PM

This is a job for someone who knows something about the G36, proper alignment tapes, and good test equipment is required.. You might consider using a tape that is reasonably compatible with the deck's current settings. I've found surplus BASF Audio Professional amongst others to work well on my half track (I converted it) G36 as well as stock G36.

It is possible that some more modern tape formulations (mostly vintage exotic Japanese tape from Maxell, etc.) may not be compatible with the recorder due to the amount of oscillator power available.

simon7000 19th April 2011 08:42 PM

Are you using it in stereo or mono? If both channels are the same in stereo that would suggest everything is working. If the problem is too much high frequencies that would indicate the head alignment is at least adequate. About the only reason to adjust the alignment is for a new head or after some idiot has been playing with it.

I assume you have a previously recorded tape you are using for a reference. This will be missing high frequencies, if the heads are dirty, if the playback head azimuth is off or if there is residual magnetism on anything in contact with the tape. So you need to be sure the playback is working correctly before you do anything else.

I assume the meters work. You should be able to produce test tones with your computer.

Test tones should be recorded at a level of -20 on the built in VU meters.

If you record the tones and they do not playback within +/- 3 db then try replacing the tubes. Changing tubes is the easiest and most important service issue.

The only real adjustment is the bias. You can change the frequency a bit with trimmer capacitor #1 and the levels with trimmer resistors 10 & 11. If you note where you found them playing a bit should not hurt anything.

Salli 19th April 2011 09:52 PM

Thanks for your responses.

Having read your coments I think the only thing I need to set is bias. Can someone please give me a simple guide to do that? The oldness of this machine scares me and I don't want to screw it up.

I spoke to the previous owner and I think the G36 has never been adjusted since the 60s. From what I've read Ampex 456 requires a different bias setting to typical 60s tape, but it could be a matter of taste perhaps.

Also should I be using the Diode or Radio inputs? Diode seems to sound clearer but it's hard to tell. I'm recording onto the G36 directly from a mixing desk's stereo monitor output (rather than the XLR outputs).

cbdb 19th April 2011 10:34 PM

If this machine came out of a pro studio it was probably fully aligned and biased for every project and the particular tape the engineer/producer had and then some engineers would tweak the bias or rec gain to change the compression level, noise etc. I guess what Im saying is that you have know idea how its aligned (or probably misaligned) and needs to be aligned by a professional (or self educated by the internet) for the particular tape used. This requires a test tape and a scope to physically align the head (and possibly even the tape guides) before you can tweak any electronic.

Setting just the bias is easy. One popular method:while recording a 20hz tone and playing back off the repro head turn up the bias until the tape noise is a minimum.

AuroraB 20th April 2011 07:30 PM

IF you don't already have the service manual for the G36, try and get one -probably available off the net. The manual will describe exactly what to do. I have an A77 with the original manual, and also a copy off the net, which would describe the procedure, but I'm away from home base, and on a slow connection, so I cannot help you directly.

Starting with 1 kHz and adjusting levels, and then 10 kHz and adjusting bias for equi levels seems more correct, ... last time I did this must be 25 years ago...........

simon7000 20th April 2011 09:24 PM

The G36 is a consumer machine. The only adjustments are for bias. One for left one for right. The only other "adjustment" is to change the tubes. You can record and listen at the same time as you adjust the bias.

Since the previous owner did not change any of the head adjustments leave them alone.


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