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Old 9th February 2004, 02:32 AM   #1
marz.tv is offline marz.tv  Sweden
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Default tape alignment hell

I'm not sure if I should post this here or at Analogue but it's kinda about tubes I guess....
Someone borrowed my two track Revox G36 and when I got it back I realized the heads were messed with. It was time anyway to CLA it so today I bit the bullet and pulled out the service manual. Unfortunately the page where head alignment is described is missing from my copy
I didn't have an original test tape, but at least a set of test tones recorded on a huge Telefunken broadcast machine in good alignment. After many frustrating attempts to spot phase shift reliably on a *single beam* scope, I dug out a tape of piano music made on the same broadcast machine from vinyl. I found it was pretty easy to set the height and azimuth of the head just listening to the music (the recorded LP hiss was good help too) through headphones. Then it was time for the record head...
To make a long story short, I finally ended up recording New Order on the tape while monitoring the playback head while adjusting the recording head. Not the most professional approach but I got in the ballpark
My question to the members are: Does anyone know of a good website that deals with tape head alignment? Or maybe some of you are old recording guys who can give me some tips on how to fine-tune the G36 (which transport is basically like the A77, B77 I think). I have signal generators, a couple of VTVMs, Tek 310A scope, a Marconi distortion meter...
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Old 9th February 2004, 03:33 AM   #2
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You need a standard alignment tape to set the playback head first then you set the record head to the playback head. Standard tapes can be expensive but not necessarily so sometimes. Just depends.....

Here is a link to Magnetic Refrence Labs. They make just about the best alignment tapes available and I have use them on both Studers and Nagras many times. I presently have a two track 15 IPS MRL tape that I keep my Technics RS 1500 two track tuned up with.
http://home.flash.net/~mrltapes/

Mark
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Old 9th February 2004, 06:58 AM   #3
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Hi,

This link may also be of help to you:

OVERHAULING A REVOX G36

All the best with this fine machine.

Cheers,
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Old 9th February 2004, 07:59 AM   #4
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Back way back when this was the reference manual of choice - Standard Tape Manual

The method that I was taught (and used) to set record head height was to record say 400Hz at high level (into overload is ok) in one direction, flip the reels and record the same section in reverse direction, then dip this recorded section into a vial of alcohol wth very fine iron oxide particles in suspension.
The particles will attract to the magnetised tape tracks and when the alcohol evaporates are clearly visible.
The goal is to bring the outside tracks just to the tape edges, and the three guard bands equal width.
A high power magnifying glass is required to closly confirm this condition.
As far as I know this is the only proper way of confirming correct record head height.

Eric.
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Old 9th February 2004, 06:28 PM   #5
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Once upon a time, there was some stuff called "Ediview", which was specifically made for developing magnetic tracks to allow editing of 2" quadruplex video tape. Later, some of the broadcast equipment suppliers sold a coin-sized wodget containing Ediview with a thin (non-magnetic) base and transparent top, allowing you to find the tracks on your tape. You never know, the wodget might still be available.

The general method of tape machine alignement is to align the replay head to a known good alignment tape. Assuming height is correct, adjust azimuth for maximum output at 14kHz, then finely adjust for minimum phase error. The record head is adjusted by monitoring the effect on simultaneous replay.

Tape heads should be aligned carefully and correctly when fitted, then left alone. Constant fiddling ensures that they require constant alignment. I trust that you have carefully and clearly explained your displeasure to the person who screwed up your machine whilst slowly removing their manual extremities.
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Old 9th February 2004, 07:15 PM   #6
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... of course bias and EQ settings are different for every tape formulation that you use.
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Old 9th February 2004, 07:44 PM   #7
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There is a product called "Magview" that can be used to set the recording head height and get the guard bands properly spaced.

http://www.genevagroupofcompanies.co...l_prod__5.html
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Old 9th February 2004, 10:29 PM   #8
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Thanks for your helpful replies. Dang, I had forgotten about that trick to develop tape. I have it outlined in an old book about hifi from 1969. Also I think it is time to start looking for a dual beam scope... Jukka Tolonen (thanks Frank! although I had seen it already, that's about the only tech site on the net about the G36) suggests using clear tape and marking the visible tracks with a felt pen. But seeing what is recorded would be even better.

I'm attaching a cozy image of my working with the innards (swapped a couple of old electrolytics while I was at it)
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Old 9th February 2004, 10:39 PM   #9
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Hi,

I see you pulled out the amplifier section.
Any particular reason for doing so?

Cheers,
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Old 9th February 2004, 11:47 PM   #10
marz.tv is offline marz.tv  Sweden
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I kind of knew that question would arise
A few years ago, I got the 'nice' Revox as a 4 track machine, and an ugly 'parts' machine that was 2 track and *38cm/s*. I swapped the capstan, motor, head stack and did the circuit mods described in the manual and finally got a great machine for hifi and home studio work, compatible with modern 1/4 inch mastering machines.
I then borrowed the output transformers from this one and and the parts machine for my first serious tube amp project. Originally, I had intended to make a compact ECL86 amp using the whole amp section from the recorders. Then the DIY bug bit me and it became quite another amp (see the photo gallery). I thought of putting the amp section back (sans trannies) for originality, but haven't gotten around to it yet... Generates less heat and lowers the current draw without it I guess.
That's the story
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