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Old 7th August 2008, 05:14 PM   #1
kevinkr is offline kevinkr  United States
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Default Restoring ReVox G36 MKIII - Expert Opinions Solicited

I resurrected an old thread on the revox, so far the only responses have been to the original post from over 3yrs ago so I will not make that mistake again.

Anyway this fairly nice ReVox G36 MKIII 117V North American edition half track recorder fell into my lap recently and although I have worked on many of these decks and am relatively comfortable working on it, it has been a long time since the last one.

Long enough that although the selenium rectifiers and electrolytics all test good I seriously think I should without question replace them. Seems logical except that the design is so efficient that I will have to make significant changes to get voltages right. The only source of drop in replacement caps (vibroworld) seems to be gone, and no one seems to be able to tell me whether most decks still running are still using the stock supply components. Realistically at 42yrs out I would assume this is skirting disaster.. It's just that this deck is virgin and I want to do the updates with comparable parts that don't leave it looking like a hack worked on it.

This machine seems to be a low hours unit and hence should have a long remaining service life with care.

I'm also planning on some mods. Charlie King recommends removing the 5W PP amplifier which makes sense as this generates most of the heat in the electronics section due to its dissipation.

In addition the current input amplifier provides far too much gain with modern sources and basically I don't need it at all. I plan to just go right in at the recording level control. I could eliminate a further two tubes doing this if I so choose, but this would require modifying the dc filament supply. (Probably a performance enhancement actually)

I've replaced a couple of electrolytics in the replay electronics.

I have not yet run the deck, but I am told this is a high speed version. (7.5ips/15ips) I have not been able to prove or disprove this.. I have 15ips recorded tapes so that will be the acid test once I get it powered up.

Anyone have a guess as to what type of caps the motor phase shift caps are, and whether I should replace/rebuild (new caps in old cans?) On older versions these actually can present an electrical hazard due to leakage into the chassis. The 117V version runs the motors off of a dedicated winding on the power transformer and the motor circuitry is fully isolated from the mains.

I've provided a schematic of my version for the curious or helpful.

I'm really looking for insights, comments, advice and encouragement from people who are still working on these decks.
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Old 7th August 2008, 08:01 PM   #2
Horexx is offline Horexx  Germany
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Look here:
Overhauling a Revox G36

http://koti.mbnet.fi/siliconf/JukkaT...vox/revox.html
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Old 7th August 2008, 09:00 PM   #3
kevinkr is offline kevinkr  United States
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Quote:
Originally posted by Horexx
Look here:
Overhauling a Revox G36

http://koti.mbnet.fi/siliconf/JukkaT...vox/revox.html

Thanks, I've seen it, and read it.. Really looking for recent direct experience..
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Old 9th August 2008, 10:41 PM   #4
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bump....
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Old 9th August 2008, 11:22 PM   #5
EC8010 is offline EC8010  United Kingdom
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I'm wondering why anyone would refurbish a Revox G36. After all, the transport is nothing to write home about. Why not refurbish a (professional) Studer A80 or later?
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Old 11th August 2008, 03:32 PM   #6
kevinkr is offline kevinkr  United States
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Quote:
Originally posted by EC8010
I'm wondering why anyone would refurbish a Revox G36. After all, the transport is nothing to write home about. Why not refurbish a (professional) Studer A80 or later?
I'm not sure I can give a rational answer that question as I also have an Otari MX-55-T-M studio recorder which is quite nice.

I'll try though.. In this case unworn stereo half track heads, low hour machine, 3 motor design on a reasonably if not the most rigid chassis. Photo electric tape path sensing. (It's a MKIII) Vacuum tube audio path. Takes 10.5" reels. And mechanically it is in fine working order. Playback is fine, recording has some issues with dirty switches. (I've done some mods as well as repaired a variety of minor issues.)

I was hoping it was the rarer 15ips version, but it's not. I may look for a high speed capstan assembly at some point. (Why won't the site allow the legitimate abbreviation for assembly??) Parts are not too hard to get. They sound good when working properly? Emotional attraction - I've wanted one since I was 17.. What more can I say to justify it. I like the machine, it's retro and solidly built. It came to me rather unexpectedly and I am happy to give it a new home.

I'm not sure exactly what your objections to the transport are, for its day it was about the only commonly available consumer deck with 3 motors and a direct drive capstan available here in N.A. I think that makes it notable, and worthwhile compared to any single motor deck out there. Performance numbers for wow & flutter are respectable and generally better than the specs would indicate. The heads are decent performers, but far better heads are available and can be installed. For my planned usage the stock heads are more than good enough.

These old ReVox machines are the only vintage recorders other than later Ferrographs, and Ampex 350 series gear that I have any interest in. Certainly not sota, but far far better than most vintage Japanese consumer grade decks for the same sort of money.

Not sure what is going on in regards to tape on your side of the pond, but there has been quite a renaissance in interest in open reel tape and the machines to play them here. Enough that I am taking notice.
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Old 11th August 2008, 05:46 PM   #7
EC8010 is offline EC8010  United Kingdom
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My objection is very simple; you can pick up a real studio machine with real (and reel) servos, capstan servo etc for the same as a G36. In fact, broadcasters give them away. The Studer A80 is a beautifully engineered machine and built like a battleship. Unfortunately, it takes up almost as much room...
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Old 11th August 2008, 06:23 PM   #8
miklos is offline miklos  Canada
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The A80 is a monstrous machine, you need two people to move it around, not practical at all. The portable recorder is less problem. Remove the tubes you mentioned, replace the electrolytics, and if it's ok leave the selenium rectifier alone. Your idea to go directly in to the level control is a good one. The motor capacitors are not electrolytics ,so they are still ok. Good luck. Miklos
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Old 11th August 2008, 07:06 PM   #9
kevinkr is offline kevinkr  United States
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Quote:
Originally posted by EC8010
My objection is very simple; you can pick up a real studio machine with real (and reel) servos, capstan servo etc for the same as a G36. In fact, broadcasters give them away. The Studer A80 is a beautifully engineered machine and built like a battleship. Unfortunately, it takes up almost as much room...

Yeah, I have a friend who has one, it's just way too large for my listening room.. I have one full servo Otari, and can get another.. (5050 etc..)

The G36 landed in my lap and I have literally nothing in it but a few hours of my time.
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Old 11th August 2008, 10:14 PM   #10
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Quote:
My objection is very simple; you can pick up a real studio machine with real (and reel) servos, capstan servo etc for the same as a G36. In fact, broadcasters give them away.
Hi -

Have any contact info for these broadcasters?
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