Hi, It's about Quad's & Revoxes

stefaan · 9th March 2006, 02:39 AM

I just became a member of DiyAudio - from Belgium.

I know everything about Quad amplifiers between 33 & 606.

I am working on the Revox A77.

Take a look @ http://quadrevisionspot.blogspot.com/

Stefaan

Jan Dupont · 9th March 2006, 05:42 PM

Welcome to the forum

Nice site you have there about Quad

anatech · 10th March 2006, 12:37 AM

Hi Stefaan,
Welcome to DIYaudio! Great Quad site!

With the A-77, replace all those white tantalums with electrolytics, even on the capstan motor servo board. The trimmer controls fall apart easily. Don't know if you knew that yet or not.

-Chris

stefaan · 10th March 2006, 02:04 PM

Hi, Cris,

Yes, I know, all those caps should be replaced.

There even were some which gave a short-circuit!

A problem with the Revox-modules is that not every component of the same circuit is on the same PC-board so it is very difficult to test a board outside the machine

Stefaan

rayfutrell · 10th March 2006, 06:56 PM

I bought an A77 in 1970 which had 3 problems. The relays on the motor control board did not have contacts with high enough current rating so the contacts would erode and stick. Replaced the relays with relays having 5 ampere contacts.

The 5 watt resistors on the same board were too small and they would overheat and char. Replaced them with 10 watt resistors.

The friction material on the brake drums was a synthetic which would get stickey if it got hot (heavy brakeing) and then stick to the brake band when it cooled and prevent the reel motor from turning. Replaced the friction material with an all cotton fabric.

Regards,
Ray

anatech · 10th March 2006, 08:02 PM

Ray,
You missed all those darn caps!

Brake bands are normal maintenance items. Your's sounded like they were very old. The relays can go bad, not that much of a problem. The bearings tend to go. Very easy replacement. On and on. Oh yeah. The counter belts always seem to break, and the older counters that use a toothed belt, newer ones used gears.

-Chris

rayfutrell · 13th March 2006, 12:40 PM

You are right about the counter belt. It did eventually go bad. The A77 ran fine for 10 years and I replaced it with a B77 in 1981.
Ray

anatech · 14th March 2006, 01:11 AM

Hi Ray,
I like the "B" better, for so many reasons. The "A" is nice still.

-Chris

9th March 2006, 02:39 AM	#1
stefaan diyAudio Member Join Date: Mar 2006 Location: Antwerpen	Hi, It's about Quad's & Revoxes I just became a member of DiyAudio - from Belgium. I know everything about Quad amplifiers between 33 & 606. I am working on the Revox A77. Take a look @ http://quadrevisionspot.blogspot.com/ Stefaan

9th March 2006, 05:42 PM	#2
Jan Dupont diyAudio Member Join Date: Apr 2003 Location: Copenhagen, Denmark	Welcome to the forum Nice site you have there about Quad __________________ Free Schematic and Service Manual downloads www.audio-circuit.dk, Company: www.dupont-audio.com, Joint venture: www.DupontMantra.com

10th March 2006, 02:04 PM	#4
stefaan diyAudio Member Join Date: Mar 2006 Location: Antwerpen	Revox capacitors Hi, Cris, Yes, I know, all those caps should be replaced. There even were some which gave a short-circuit! A problem with the Revox-modules is that not every component of the same circuit is on the same PC-board so it is very difficult to test a board outside the machine Stefaan __________________ http://quadrevisionspot.blogspot.com/

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10th March 2006, 12:37 AM	#3
anatech diyAudio Moderator Join Date: Jun 2004 Location: Georgetown, On	Hi Stefaan, Welcome to DIYaudio! Great Quad site! With the A-77, replace all those white tantalums with electrolytics, even on the capstan motor servo board. The trimmer controls fall apart easily. Don't know if you knew that yet or not. -Chris

10th March 2006, 06:56 PM	#5
rayfutrell diyAudio Member Join Date: Sep 2004 Location: virginia	I bought an A77 in 1970 which had 3 problems. The relays on the motor control board did not have contacts with high enough current rating so the contacts would erode and stick. Replaced the relays with relays having 5 ampere contacts. The 5 watt resistors on the same board were too small and they would overheat and char. Replaced them with 10 watt resistors. The friction material on the brake drums was a synthetic which would get stickey if it got hot (heavy brakeing) and then stick to the brake band when it cooled and prevent the reel motor from turning. Replaced the friction material with an all cotton fabric. Regards, Ray

10th March 2006, 08:02 PM	#6
anatech diyAudio Moderator Join Date: Jun 2004 Location: Georgetown, On	Ray, You missed all those darn caps! Brake bands are normal maintenance items. Your's sounded like they were very old. The relays can go bad, not that much of a problem. The bearings tend to go. Very easy replacement. On and on. Oh yeah. The counter belts always seem to break, and the older counters that use a toothed belt, newer ones used gears. -Chris

13th March 2006, 12:40 PM	#7
rayfutrell diyAudio Member Join Date: Sep 2004 Location: virginia	You are right about the counter belt. It did eventually go bad. The A77 ran fine for 10 years and I replaced it with a B77 in 1981. Ray

14th March 2006, 01:11 AM	#8
anatech diyAudio Moderator Join Date: Jun 2004 Location: Georgetown, On	Hi Ray, I like the "B" better, for so many reasons. The "A" is nice still. -Chris

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