Author Topic: A new lease on life for an old Revox G36  (Read 11222 times)

Offline witblits

A new lease on life for an old Revox G36
« on: January 20, 2012, 09:04:20 AM »
So I got my Revox G36 back from Steerpike after a major clean-up and repair and was prompted to write a little about it.
I am not going to go into any technical detail except to quote the following from http://www.reeltoreel.de/worldwide/G36.htm “The REVOX 736 (G36) is a mono/stereo machine with stacked erase heads, separate recording heads separate replay heads, six audio pre-amplifiers. and a push/pull power amplifier. Tape speeds of 3 3/4 and 7 1/2 .i. p. s. are obtained by pole-changing the synchronous Papst capstan motor. Twin-track and four-track models are available, both fully stereo phonic, recording to the latest C.C.I.R. (DIN 45113) characteristic.”

This unit was found in an old building in JHB and was covered in pigeon droppings and years of dust.  The building use to belong to Gallo recordings and was used as a recording studio in the 40’s. Steerpike has given it a new lease on life and I must say it sounds amazing. It has a clear but not harsh and slight warm sound. I find it difficult to choose between this RTR and the rest of my collection.

It is original except for a missing cover below the head block, a counter unit and a lid for the case. I am running it through a Rotel pre and power combo and a set of Focal JM Labs Chorus 714 S speakers.

The rest of my RTR’s are a Revox (B77) and a newer Tascam br 20 from EMI.

Thanks again Steerpike maybe you can add a little bit on the restoration work.
Ek is dalk n aap maar ek is n ou aap

Offline Steerpike

Re: A new lease on life for an old Revox G36
« Reply #1 on: February 04, 2012, 02:06:30 AM »
This machine was severely neglected - as you described - but luckily not badly abused.
All the electrolytic caps had to be replaced: only about 4 in the signal path, but 3 triple can types. Out came the cans and in went a PC board which took the 9 new radial PCB types. The three selenium rectifiers were replaced too.
A weak point on the G36 is the pushbutton assembly. The phosphor-bronze contacts break. Luckily on this one only one non-moving contact had broken, and I harvested a substitute from an old relay.
The counters also fall apart - they are made of plastic that becomes brittle. I plan on making an electronic LED counter to fit my G36 one day.
All three motors lubricant had dried out, so that was replaced. The motors are quite straightforward to disassemble though, and the bearing do not wear unless the machine is very, very well used.
This machine is super sensitive to head grime - and the heads are difficult to access for cleaning. When they are clean, it has a good frequency response, and a very stable stereo image.
The pinch roller got a substantial grinding down to expose soft pliable rubber.

The cathode follower outputs need to see a load of 100k or higher, otherwise bass response is affected. I did bring +24v Dc out on the now-defunct remote control socket, which can be used to power a solid-state output buffer if one is ever required.
Despite its condition, all the potentiometers were in good condition, not producing any scratchiness when adjusted. This is a bonus since the odd hollow shaft style will make it difficult to fit modern replacements.

The only adjustments are record level (operating flux) and record bias, so tape type is important - you cannot tweak the equalisation to suit dull or bright oxide formulations! Some people increase the bias + erase oscillator frequency from the original 70kHz, but I have no experience of whether this is really a good thing or just a change, not necessarily for the better.

There is also no comprehensive source/minitor switching. VU meters (true VU, with no peak indication) work on the record amplifiers only, and you cannot route the input signal through to the line-out for monitoring before record starts, nor do tape/source switching during record. Confidence monitoring only!
This is all because Revox expected such switching to be done on the pre-amp, and all monitoring to be done via the internal mono amp. The internal amp is in fact quite good, and is identical to that used in the Revox 40 integrated stereo amp. The inboard speaker isn't too impressive, mainly due to the cabinet's total lack of acoustics. But an external speaker or headphones (mono) does give very good sound. Originally the G36 had one of several variants of Philips dual cone 8" speakers, but years in a damp environment had caused this one to collapse, so it got a modern replacement.

Remarkably, new heads are still available. They are not interchangeable with the A77 & B77 heads. Genuine from Studer carry a nice price of around R5000 for a set!
This one's heads still have a good few hundred hours in them.

Offline Ampdog

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Re: A new lease on life for an old Revox G36
« Reply #2 on: February 05, 2012, 04:23:45 AM »
Steerpike (and Witblitsh),

Most interesting! [Mod hat on: Drooling allowed - Mod hat off]

Really wish I could know where to go scavenging. (Now my very good friend Charles - occasionally posting here - is a Hero scavenger ... but he won't reveal where to go. MA!!)

Nostalgia: During the 50s I had access to a friend's Ferrograph (3,75 - 7,5 - 15 i.p.s.), which was transportable rather than portable. Wish I could get hold of one somewhere!

...and to do what with these days?  Don't ask silly questions.
Audio must be the only branch of engineering where lack of basics' knowledge is considered a superior form of wisdom. (Anon)

Offline Steerpike

Re: A new lease on life for an old Revox G36
« Reply #3 on: February 05, 2012, 02:26:07 PM »
On my own first G36 I removed the pushbutton assembly entirely (decades ago), and replaced it with relays and tactile microswitches. The result is much more durable, but does ruin its 'originality'.
G36 (and the earlier F and E 36) are transport-wise, rock solid and almost impossible to break. No moving parts, no belts, no clutches, nothing wears out except the heads. Far more stable than any of the domestic Japanese machines, but the Revox isn't as operationallty slick, so they get overlooked when only a brief evaluation is done. The amplifiers are straighforward triode cathode-follower or common-cathode throughout, using only ECC81 and ECC83. All easy to mod or tweak if you so desire.

Tape-aids-for-the-blind, and the JHB planetarium used many G36s in the 1960s.

There were three versions of the G36, i.e., two revisions. The obvious change was an optical end-of-tape sensor in the last revision, and the addition of inductor bias traps. The earlier revision involved changes to the wiring of the winding motors, to provide better tension switching during mode changes - it's is a revision anyone can do, no new parts needed.

If you see a G36 with the square heads (not the cylinder style) those are new heads and it is well worth checking out. Just hope somebody didn't mistakenly put A77 heads in it, as the revised G36 heads look the same as the A77 heads.
And if you ever find an original 15 ips G36 - grab it immediately! They are rare and very desirable.

Don't be put off by a missing case lid - they were simple plastic (same as the base) with a vinyl trim inlay, and they get to look rather tatty.  E36 and F36 are rare in SA, but still nice machines. They will not take NAB reel hubs though - only the small cine hub reels, which are what almost all 7" reels are, but in 10.5" size reels, are not so easy to find.

Pia Bouwmann (the late Wim's wife, Mr valve) had a 1/4 track G36 to sell a while back. I think she sold it in with the whole Mr Valve business, so the new owners may still have it and want to sellit.
« Last Edit: February 05, 2012, 02:28:26 PM by Steerpike »

Offline witblits

Re: A new lease on life for an old Revox G36
« Reply #4 on: February 06, 2012, 08:59:44 AM »
I have since done some recording with the unit and must say this unit is now my favourite.
Ek is dalk n aap maar ek is n ou aap

Offline GMaestro

Re: A new lease on life for an old Revox G36
« Reply #5 on: February 06, 2012, 08:48:44 PM »
I am sure I had some old Revox Reel to Reels standing around in the dust which we took from the Studio's of Radio Pulpit.

Will have a look if they still exist , if they do will post some pics.

Pretoria

Offline Steerpike

Re: A new lease on life for an old Revox G36
« Reply #6 on: February 06, 2012, 09:03:11 PM »
ooooo.... culd be a PR99 or two... i'm interested!

Offline GMaestro

Re: A new lease on life for an old Revox G36
« Reply #7 on: February 06, 2012, 09:33:01 PM »
Some Reel to Reel Stuff..









Pretoria

Offline Agaton Sax

Re: A new lease on life for an old Revox G36
« Reply #8 on: February 06, 2012, 09:44:41 PM »
Are these for sale? I dropped my Studer B62 :'( (last pic) and desperately need a spares machine.

Offline GMaestro

Re: A new lease on life for an old Revox G36
« Reply #9 on: February 06, 2012, 09:49:25 PM »
Yes they probably are, just note I haven't tested any of these so I am not even sure if they work or not.

I will need a day or two to get them all out and test them. There are a few more Revox ones as well.

Then I can test them and make some prices.

Pretoria

Offline Steerpike

Re: A new lease on life for an old Revox G36
« Reply #10 on: February 07, 2012, 12:20:37 AM »
^^^ THAT G36 has the new heads.
The Studer is the nicest of them, but does it have the separate amplifier box? Stereo?

If there are any non tape-recorder Revox bits (amp, speaker etc) please let me know too!

How long has radip pulpit been going? Those machines are quite vintage - i didn't think the station was as old as that - or maybe they bought them used?

Offline GMaestro

Re: A new lease on life for an old Revox G36
« Reply #11 on: February 07, 2012, 10:34:34 PM »
The Station is quite old.

My Father worked for them about most of his life. He is about 75 years old now and since I can remember he started working for them when he was very young.

I also worked there for a while, when I was 17 years old that is about 14 years ago they still used the Revox machines like crazy. I used to play the tapes on air for them. About 4 or 5 Machines in a row per studio.

But now they are totally digital. With a massive server room where they keep all the audio data. All of the Reel to reel's and tape deck's has been thrown out.

My Father said they took all those machines and dumped it in the junkyard.... What a waste!!

Some of the revox machines had Valve amps inside. One of them I disassembled and built out the valve amp , using it for my hi-fi. Very good sound indeed.

Most of the units you see here is probably not in working order.
Apparently the Studer has already been stripped for electronic spares. I think it still has the motors and mechanical parts, but I am not sure.

As soon as I get the time I will post all the pics with the prices on them. All will be sold "AS IS"

« Last Edit: February 07, 2012, 10:42:40 PM by GMaestro »
Pretoria

Offline witblits

Re: A new lease on life for an old Revox G36
« Reply #12 on: September 11, 2012, 01:47:44 PM »
Hi GMaestro

Any news on these Reel To Reel recorders
Ek is dalk n aap maar ek is n ou aap