Carver C19 Pre amp and TFM42 main amp
Just as I though the day could not get any worse, a long standing client came in with this pre and main amp collection.
Now I have a regard for Carver gear, I have repaired a couple of valve pre amps in the past and I have to say they sound very good and the tone controls seem to act on lower than normal bass frequencies and higher than normal on the trebles.
The report on this setup was a really loud noise when powered up. I checked the pre amp first, being a coward and found all the user controls, switches and potentiometers all bad. Injecting cleaning fluid into the whole lot made things much better. Intermittent pops and bangs were traced to dry joints around the series regulators and a few other areas. Finished, the pre amp was now good.
Thinking I had resolved the issues, I connected a set of speakers up to the main amp and powered her up with current limiting. All seemed to be okay, so I switched out the current limit and all hell broke loose. Speakers flew across the room and looking at the mains current, the amp was drawing enough to power Birmingham for a week. I had a diagram for this amp and its one of these fancy things with various stages in the output section, 3 in all, which all kick in when you demand a bit of clout, bass drum and so on. Current dumping. The service manual is quite detailed and the set up procedure is like trying to bring back Apollo 13 using a slide rule. Even the mains supply has a strange triac switching arrangement. You really do need a week on hard drugs before having a go with this. Looking at the output on the scope, one channel was banging between supply rails ay about 10Hz, the other had little output. Cutting a long story short, the bias and balance presets, were either open circuit or intermittent. All had to be replaced. After setting up and making sure both channels performed equally, all was well in the camp. Off for a little snooze.