atkelar | Restoration Project #34 - Revox A72x - Part 2 @atkelar | Uploaded April 2022 | Updated October 2024, 3 hours ago.
About half a year ago, Emil - an online friend from Germany - asked if I would be interested in saving a Revox A720 receiver/pre-amp from the scrap bin - it would need some TLC and repairs but would be "shipping only" otherwise. As I was looking for a pre-amp to connect with my turntable, I took up the offer right away! It did look interesting, even though I never heard from that brand much less that particular model before... but I did snatch up a reasonably priced A722 amplifier that goes with it.
In this episode, I cover the assembly of the units and do some troubleshooting; yes, not everything works on the first try around here. But at least nothing blew up!
One of the more annoying issues is that the schematics that are out there seem to have some errors in them; specifically the PCB layouts have some components flipped 180°. It cost me a TTL counter IC and quite a bit of hunting down an issue that was caused by a reversed tantalum. Not to mention that just by the number of caps I replaced here, I had two upside down on my own account.
The alignment guide uses a VTVM... and I do have one since last year! Yay! Useful tool restoration!
Getting the amplifier up to speed and working also included a bit of troubleshooting...
While I did record a bit of troubleshooting footage, I found that it was not really... all that appealing. It was basically just poking at random contacts and off-screen head scratching. So I did some presentation/explanation segments instead.
0:00 Intro / Rotary Switches / PCB Repair / RIFA!!! / Nixie Dusting
2:05 Assembly Time! Frame and Wiring Loom / Transformer
3:10 Power Supply Adjustment and Test / Input Amplifier PCB
3:50 Tuning Matrix
5:28 Switch and Selection Boards / Nixies / Meter Board
5:55 Factory Botch explained / Added
6:35 First Test Results
7:08 Amplifier Power Supply Board
8:24 Transformer Connections / Fan Motor
9:16 Input Signal Wire Fix / Amplifier Chassis
9:58 Amplifier Heat Sink / Input Sockets
11:07 Wiring the Amplifier / Test!
12:13 Output Delay Relay Fix / Nixie Turn On!
12:45 Signal Meter Replacement / Trimmer Mod
13:49 Radio Receiver Overview / PCB connections
14:48 Radio Signal Problem / PCB Errors in Schematics!
15:55 Audio Quality Problem
16:29 Wood Panels
17:48 Knob Replacements
18:23 Front Panel "Fixup" (including Silk Screen Problems)
19:20 Can I haz Music? Not yet!
21:12 Transistor Cooling Improvement / Final Words and Future Projects?
22:00 Impressions
22:47 Outro / Outtake
Music:
My Train's A Comin'
Unicorn Heads
(YouTube Audio Library)
You can support me on Ko-Fi: ko-fi.com/atkelar
About half a year ago, Emil - an online friend from Germany - asked if I would be interested in saving a Revox A720 receiver/pre-amp from the scrap bin - it would need some TLC and repairs but would be "shipping only" otherwise. As I was looking for a pre-amp to connect with my turntable, I took up the offer right away! It did look interesting, even though I never heard from that brand much less that particular model before... but I did snatch up a reasonably priced A722 amplifier that goes with it.
In this episode, I cover the assembly of the units and do some troubleshooting; yes, not everything works on the first try around here. But at least nothing blew up!
One of the more annoying issues is that the schematics that are out there seem to have some errors in them; specifically the PCB layouts have some components flipped 180°. It cost me a TTL counter IC and quite a bit of hunting down an issue that was caused by a reversed tantalum. Not to mention that just by the number of caps I replaced here, I had two upside down on my own account.
The alignment guide uses a VTVM... and I do have one since last year! Yay! Useful tool restoration!
Getting the amplifier up to speed and working also included a bit of troubleshooting...
While I did record a bit of troubleshooting footage, I found that it was not really... all that appealing. It was basically just poking at random contacts and off-screen head scratching. So I did some presentation/explanation segments instead.
0:00 Intro / Rotary Switches / PCB Repair / RIFA!!! / Nixie Dusting
2:05 Assembly Time! Frame and Wiring Loom / Transformer
3:10 Power Supply Adjustment and Test / Input Amplifier PCB
3:50 Tuning Matrix
5:28 Switch and Selection Boards / Nixies / Meter Board
5:55 Factory Botch explained / Added
6:35 First Test Results
7:08 Amplifier Power Supply Board
8:24 Transformer Connections / Fan Motor
9:16 Input Signal Wire Fix / Amplifier Chassis
9:58 Amplifier Heat Sink / Input Sockets
11:07 Wiring the Amplifier / Test!
12:13 Output Delay Relay Fix / Nixie Turn On!
12:45 Signal Meter Replacement / Trimmer Mod
13:49 Radio Receiver Overview / PCB connections
14:48 Radio Signal Problem / PCB Errors in Schematics!
15:55 Audio Quality Problem
16:29 Wood Panels
17:48 Knob Replacements
18:23 Front Panel "Fixup" (including Silk Screen Problems)
19:20 Can I haz Music? Not yet!
21:12 Transistor Cooling Improvement / Final Words and Future Projects?
22:00 Impressions
22:47 Outro / Outtake
Music:
My Train's A Comin'
Unicorn Heads
(YouTube Audio Library)
You can support me on Ko-Fi: ko-fi.com/atkelar
