Revox A77 restoration project

[4thtry]

There were quite a few big reel-to-reel (R2R) tape machines at the MWAF swap meet this past year. When I was still in school, I purchased one of these big monsters brand-new with plans to go on-location with a pair of high quality microphones. I had to sell my machine and microphones to stay in school, but I never forgot that distinctive sound of a live microphone feed coming through a pair of high quality headphones.

So, on an impulse, I picked up a "dirt cheap" used/repairable Revox A77 MK II. The seller also threw in an original factory service manual, so I think I got a pretty good deal.



You will notice that the head assembly is missing in the above photo. More to follow:


Bill S.

[4thtry]

Re: Revox A77 restoration project

When I got home with the machine, I hooked it up and ran some tests. Fast forward, rewind, and play seemed in fairly good condition. No pinch roller binding or squealing noises. The tape loosened up a bit when I hit the stop button, so some minor adjustment is probably needed on the brakes.

After cleaning the pots & several connectors, I hooked the aux inputs to an old FM receiver and discovered that both channels will pass a clean, undistorted low level audio signal from input to output, so the input amplifier card and the two playback amplifier cards are probably OK.

I cleaned the heads and then loaded some old 1/4" tape and attempted to record a stereo FM broadcast. The left channel seemed to record and playback OK but the right channel did not. It was low in overall output with a significant loss of treble. Moreover, the bad channel had a low frequency bubbling type noise floor that drifted in & out. The tape heads and/or something in the right channel record amplifier card needed attention.

Also, for some odd reason, the balance control worked in the opposite direction that it should have worked. Turning it all the way to the left reduced the right speakers output and turning it all the way to the right reduced the left speakers output. And the record level controls work on the wrong channels. Rotating the left channel record level up and down affected the right channel's VU meter level. Rotating the right channel record level control up and down affected the left channel's VU meter level.

At this point, I had to make a decision. Should I attempt to restore this 40+ year old machine? Was it worth it or should I quit before getting in too deep?

To help with the decision, I removed the entire head assembly and put each head under "micro" magnification. There was "some" wear on all 3 heads. And there was a very small diagonal trench cut at an angle across the record head. Could these heads be relapped? Was the diagonal trench too deep to repair? I had no idea.

Assembly:



Record head:



Record close-up:



Play head:



Erase head:




So, roughly 2 weeks ago, I double boxed the head assembly and mailed it off to a head re-lapping service with instructions to examine, relap, and optically align, if possible.

Well, a couple days ago I got word via email that the relapping process was successful! So my R2R project is a go! I should be getting the assembly back next week.

That is where the project stands right now. When I get the head assembly re-installed I will run some additional record & playback tests to see if the record and bias cards are OK or if they need additional attention.

Bill S.

[donradick]

Re: Revox A77 restoration project

Very Beautiful old Revox. Glad it's gonna work out for you.
I've never heard or operated one, but they were highly praised back in the day.

I needed a 10 1/2 inch stereo R2R a few years ago, and scored a vintage Teac A-3300-SX off Ebay for cheap.
Didn't move tape at all - then I found that the solenoid was stuck , and a little oil and manual working it go it going.
Amazingly, the heads were in great shape and alignment was good for playback. One of my better scores!

[isaeagle4031]

Re: Revox A77 restoration project

Very very cool Bill! I had a r2r in high school and would love to have another

[andykriech]

Re: Revox A77 restoration project

I am amazed at what some are doing with R2R these days.
Taking these old components to a new levels.

http://tapeproject.com/

Andy.

[4thtry]

Re: Revox A77 restoration project

I am amazed at what some are doing with R2R these days.
Taking these old components to a new levels.

http://tapeproject.com/

Andy.

Cool! I bet those tapes sound!! A bit too pricy for me, though. My plan is to build a high quality 2 channel mic preamp and go on location.

Bill

[4thtry]

Re: Revox A77 restoration project

I got the head assembly back from the relapping service. The heads look almost brand-new, with highly polished surfaces and nice, smooth contours. But, because the surfaces were so highly reflective, they were extremely difficult to photograph. I used my Micro-Nikkor 105mm F2.8G IF-Ed lens on a tripod for all shots. Exposures ranged from 5 to 30 seconds, stopped down to the f16-f32 range. No flash was used. Instead, I slowly rotated a high intensity lamp (#93 bulb) around the head assembly during the long exposure. If the exposure looked bad, I re-shot using a slightly different lamp rotational pattern. I was essentially "painting with light" to get a reflection that looked good without obscuring the detail underneath the polished surface.

So here is my best attempt. I put together side-by-side comparisons so that you can clearly see the difference before and after the relapping process.

The playback head (double click on the photo twice for full magnification):



The record head. Note that the diagonal scratch cleaned up nicely (double click on the photo twice for full magnification):



The Erase head. Note that before relapping there was quite a bit of pitting on the surface, which is now completely gone (double click on the photo twice for full magnification):



The next step will be to remove the captain motor again so that I can bolt the assembly back in place.

Bill S.

[clydethecat]

Re: Revox A77 restoration project

Is your A77 a 3 3/4 - 7 1/2 machine, or 7 1/2 - 15?

[bkeane1259]

Re: Revox A77 restoration project

Fantastic shots Bill!! :applause:

This will be another fun thread to follow. Best of luck on the restoration and looking forward to the final results.

[4thtry]

Re: Revox A77 restoration project

Is your A77 a 3 3/4 - 7 1/2 machine, or 7 1/2 - 15?

Sadly, it is only the 3 3/4 - 7 1/2ips version. I think you can convert these machines to the high speed version, but that is not my plan. Someday, if I am lucky, I hope to stumble on an old used/repairable tube-type Revox G36 with half-track heads and 7 1/2 - 15ips speeds.

Bill S.

[4thtry]

Re: Revox A77 restoration project

Thanks, Bryan. Most of the fun is just taking the pictures. ;)

[4thtry]

Re: Revox A77 restoration project

UPDATE: I re-installed the head block assembly and tested it using some old standard output/low noise tape that I had on hand. The re-lapped heads performed well. They record & play back cleanly in both channels with low noise and good high frequency extension. The low frequency bubbling type noise, lack of highs, and low output that I heard previously on one channel is now gone. My guess is that removal of "pitting" across the surface of the erase head cleaned up the sound quality significantly.

One of the two VU meters deflected at a very low level, roughly 10-15dB less than the other. So I swapped the two record amplifier boards and the problem moved to the other channel. Further testing revealed a bad 25uF electroytic capacitor (C507) in the VU amplifier circuit (Q503). So I replaced C507 and now both VU meters work perfectly. I'm glad the problem was an inexpensive cap and not the VU meter itself, because these small meters (only .75x1.5" in size) are quite pricy ($100+)!

In a previous post, I mentioned that the record level controls affected the opposite channel's VU meters. But this was a misunderstanding on my part. When the two record buttons next to the VU meters are in the "out" position, then the tape recorder acts as a monophonic mixer to mix the two incoming channels to the opposite channel. This is the way the recorder was designed. But when the two record buttons are pressed "in" for making normal stereo recordings, then the channels are not reversed. So my machine was always functioning as it should; I simply misunderstood the monophonic "mixing" function that the Revox engineers built into this recorder.

Bill S.

[howard]

Re: Revox A77 restoration project

Thanks for sharing. I have an old Teac that needs some of the same work.

[johnastockman]

Re: Revox A77 restoration project

I got a TEAC 4010 at a second-hand store around 1995. The solenoids stick and I found a local shop that could service it for me. Alas, my physical condition deteriorated enough that travel to Seattle is not possible anymore. I suppose I could do it myself, but it's a heavy beast at 49lbs! Mark65 was interested in buying it from me, but the shipping costs from Onalaska, WA to Arizona was unbelievably costly, nixing the sale because it simply cost too much. It needed to be packed very well, double-box with styro inserts, air-packs and bubble wrap, but that was not much compared to actual shipping. Mark obviously had to decline for that much shipping costs, so I still have it. My uncle Al gave me some of his 1968-vintage stereo gear which included an Akai R2R that works so well, and I hooked it into my vintage set up. Here's theTEAC:




The Akai:



Yes, that Akai has an 8-track player in the side of it...it is 1968-vintage after all! The 8-track tapes my uncle gave me are so old, every one I tried to play, the tape broke immediately when I played them. In spite of that, the R2R part works and records great. I got a bunch of blank reel tapes from an old friend that I used to work with in radio/FM broadcasting and they are all in terrific shape, no deterioration of the tape itself. The TEAC is still available, but I think it'll be kept for "local pickup only"! Those shipping costs were quoted about 5-6 years ago, so I don't believe they have changed much, probably higher now. If you do find one, let me know, I love seeing those old R2R machines.


John A.

[4thtry]

Re: Revox A77 restoration project

I got a TEAC 4010 at a second-hand store around 1995. The solenoids stick and I found a local shop that could service it for me. Alas, my physical condition deteriorated enough that travel to Seattle is not possible anymore. I suppose I could do it myself, but it's a heavy beast at 49lbs! Mark65 was interested in buying it from me, but the shipping costs from Onalaska, WA to Arizona was unbelievably costly, nixing the sale because it simply cost too much. It needed to be packed very well, double-box with styro inserts, air-packs and bubble wrap, but that was not much compared to actual shipping. Mark obviously had to decline for that much shipping costs, so I still have it. My uncle Al gave me some of his 1968-vintage stereo gear which included an Akai R2R that works so well, and I hooked it into my vintage set up. Here's theTEAC:

[ATTACH=CONFIG]60452[/ATTACH]


The Akai:

[ATTACH=CONFIG]60453[/ATTACH]

Yes, that Akai has an 8-track player in the side of it...it is 1968-vintage after all! The 8-track tapes my uncle gave me are so old, every one I tried to play, the tape broke immediately when I played them. In spite of that, the R2R part works and records great. I got a bunch of blank reel tapes from an old friend that I used to work with in radio/FM broadcasting and they are all in terrific shape, no deterioration of the tape itself. The TEAC is still available, but I think it'll be kept for "local pickup only"! Those shipping costs were quoted about 5-6 years ago, so I don't believe they have changed much, probably higher now. If you do find one, let me know, I love seeing those old R2R machines.


John A.

Nice looking machines, John! My A77 is a lightweight at only 34lbs! The recorder I had when I was young was a Crown SX-724; a much heavier machine. My brother just "gave" me his Pioneer RT-1050 R2R, on an extended loan, so that I can transfer some old high speed 15ips master tapes that we made in the 70's to high rez digital format. The RT-1050 is 49 lbs and when I pick it up by the handle my entire shoulder hurts. Huge difference between the A77 and RT-1050.

My brother also lent me his Kenwood FL-180 wow & flutter meter, with 3150Hz test tone tapes for 7.5ips and 15ips. When I get it set up in the next few weeks, I'll test the wow & flutter of my A77 and post the results.

Bill