All a flutter

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thirstnhowl

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Hello all:
I'm a newb to this here forum, it's a reel pleasure being here! (couldn't help it) Anyway I'll start with a story/ question. I am a maintenence man at an ice arena and within the last few weeks my boss decided to upgrade the sound system. This included removing (from the audio rack) a vintage revox A-77 that was retired from use in 1991. Seeing the crime in turning this machine into dumpster food, I volunteered to give it a loving home. After 3 hours of cleaning what emerged from 30 years of dust and grime is a remarkable machine, EXCEPT....for the flutter that I am noticing after recording live acoustic guitar, particularly on single note playing. I intend to bring this baby in to be serviced and I was wondering just what can be done to correct this problem. I'd also like recommendations on nr software or hardware for the home enthusiast on a non-pentagon budget. Thank you.
Regards,:) Thirstnhowl
 
I would suspect a faulty pinch roller as causing the wow and flutter issue. It may have developed a flat spot or gone oval instead in round from years of idleness. Bottom line; Rubber parts have a definite shelf life, with or without use.

Cheers! :)
 
The Ghost of FM said:
I would suspect a faulty pinch roller as causing the wow and flutter issue. It may have developed a flat spot or gone oval instead in round from years of idleness. Bottom line; Rubber parts have a definite shelf life, with or without use.

Cheers! :)
Click to expand...

I also noticed that the pinch roller is very shiny in the tape path only. Do you know of a good cleaner? (I tried alchohol, 70% isopropyl. Didn't work too well)
 
The pinch roller on an A77 should be scaly in appearance, not shiny. The shiny appearance of your pinch roller tends to support Ghost's suggestion that your pinch roller is in need of replacement.

You can find pinch rollers and parts on eBay pretty easily and at reasonable prices. Be sure to keep the spacing shims that come out when you remove your pinch roller. The seller that you get the new one from should also supply a few. Align the new roller so that the tape path is centered on it.

It also helps to have an A77 service manual, also available at reasonable cost on eBay.

Below is the entry in the "Troubleshooting" section of the A77 Service Manual for Wow and Flutter:

"Mechanical Causes:
Periodic wow and flutter whose origin is in a defective pressure roller or whipping capstan axis can be recognized by observing the rotating element's rythm (pressure roller or capstan axis might be marked by a felt tip pen). Pressure roller, see also 4.4.1

If rythm of wow is identical with the rotation of the left-hand reel motor, the origin may be either mechanical or electrical. The mechanical cause may be defective bearing or misadjusted brake.

Electrical Causes:
Overly strong counter torque of left-hand reel motor can be cause for wow; check motor voltages, see table 5.9-46.

If wow occurs only at 3.75 ips, it may have its origin in too large a distance of pick-up or in the regulation circuit, (see 6.2.1).

Wow at both speeds may be caused by a defective capacitor in the RC-network R215/C209 in the regulation circuit. Replace the capacitor."​

Some of that may sound daunting, but it is not. The A77 is built like one of Studer's studio machines. That is to say that everything is on circuit cards, and it is all discrete components. Very easy to work on and built like a tank. The service manual is superb, has great troubleshooting information, and has very detailed diagrams, schematics, and parts lists. It also gives lotsa theory of operation information too.

These are absolutely superb tape machines, well worth preserving and maintaining. Check out eBay for parts, and post here, I'll try to give any help I can.

And, BTW, I have an A77 Mk III, half-track, high-speed (7.5ips and 15ips) model. It can still, at over 30 years of age, record and reproduce music that is indistinguishable from the original, with a S/N ratio that exceeds most machines with Dolby, and 30 to 20KhZ bandwidth.
 
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N7SC, good info.

Another simple few things to check with the A77.

Clean the tape path. Hard to do because of the concealed section but there may have been a sticky tape left its little deposits there.

In stop mode very gently turn the pinch roller with your finger. There should be very little resistance. If there is, the grease or oil has dried out and you need to remove it for cleaning and re oil. Getting the retaining clip off can be a pain. Getting it all back together, especially with the plastic spacer washers can be even worse. The B77 model was much easier for this.

Check the pinch roller pressure as per the manual. (sorry dont have it with me at present). There are two adjustments to make, one at the solenoid (under the grey front plastic panel) and one on the pinch roller arm. The pressure tends to get weaker with use which leads to slipping tape. You would normally tighten the tension by moving the solenoid very slightly to the right. Whenever the pinch roller is replaced you should adjust the pressure.


Cheers Tim
 
technophobia

Well that pretty much settles it, after I try cleaning the roller I'm taking it in to be serviced, aligned, biased, demagnetized and as much other good stuff as I can afford. Hopefully I'll find a good place here in Chicago.
 
thirstnhowl said:
Well that pretty much settles it, after I try cleaning the roller I'm taking it in to be serviced, aligned, biased, demagnetized and as much other good stuff as I can afford. Hopefully I'll find a good place here in Chicago.
Click to expand...

Try Deltronics on Halsted.
 
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