There are few pieces of vintage audio equipment that achieve the status of universal praise. A number of factors of course help to decide entry into the club, with exclusivity (i.e., low production numbers) certainly being one of them. But ultimately, these pieces have to deliver the goods, so quality of build and performance is an understood and expected prerequisite to get in. History then decides who actually gains admittance, and who doesn't.
In that lofty realm, the Fairchild 275 amplifier has certainly gained good standing. Employing state of the art technology for its day, solid circuit design, classic good looks, and sightings that are rarer than Bigfoot itself, it enjoys a premium lifetime membership in the club. Finally then, two of these rare beauties have now found their way to my lab. So with little published information about the restoration and actual performance of these amplifiers, I thought maybe a few AKers might want to follow along.
As with all my projects, this one begins with and is well into the assessment phase which includes tube testing, gathering published data, and a good physical inspection. In this case, however, that last element is more important than usual: These two particular amplifiers (serial nos. 547&559) were obtained from the estate of a long term engineer for a large radio station. He had started to restore them, but never finished the project, so my client obtained them "as found", missing bottom plates, mount hardware for the circuit boards, components, and with disconnected wiring. The selenium bias rectifier had been changed out for silicon, and the first B+ filter cap (made up from two separate caps connected in series) had been replaced likely previous to the amps being removed from original service (based on the style of caps installed). But the second filter caps (still in place) have failed with a very high power factor in both units, indicating that the amps were almost certainly taken out of service long ago. No doubt then, these amplifiers haven't seen AC power for decades.
My client got some really nice bottom plates made, and then sent the amps to me with the mandate to fully analyze them for any worthwhile modifications, and restoration for long term daily use. He also warned me that the engineer who started restoring them -- based on some previous gear he obtained from the man -- also had a habit of doing things uniquely "his way", which apparently produced some rather dubious returns, requiring further service for those earlier pieces. Sounds like a BOLO by any other name......
So, a few pics to get things started, and then I'll give my thoughts on where to go with these amps -- next time. Comments always welcomed.
Dave
Below: Yeah, let the drooling begin!
Below: I was going to tell the client that they were both junk, but I think I need to come up with a better story....... (black mark above the right rectifier tube of right unit is from some previous Duct Tape affair, but comes off easily enough)
Below: The undersides are a different story.....
And:
Below: But look a little closer at those new bias caps that were installed! Whoops........
And yet again..... (The ends you can't see are twisted together and grounded)
Below: I know. Tacky, tacky, tacky. But it did ultimately allow this unit to be rousted out of its slumber, and develop 60 watts RMS at 1 kHz from a 122 vac line, with the power transformer voltage tap set on 125 vac, using 6550C tubes. Bias and Balance controls were set to Fairchild specs. Amazing that those wax Good-All caps weren't leaking, as it biased and balanced easily -- although it wasn't really on long enough to find out if they were going to.......
In that lofty realm, the Fairchild 275 amplifier has certainly gained good standing. Employing state of the art technology for its day, solid circuit design, classic good looks, and sightings that are rarer than Bigfoot itself, it enjoys a premium lifetime membership in the club. Finally then, two of these rare beauties have now found their way to my lab. So with little published information about the restoration and actual performance of these amplifiers, I thought maybe a few AKers might want to follow along.
As with all my projects, this one begins with and is well into the assessment phase which includes tube testing, gathering published data, and a good physical inspection. In this case, however, that last element is more important than usual: These two particular amplifiers (serial nos. 547&559) were obtained from the estate of a long term engineer for a large radio station. He had started to restore them, but never finished the project, so my client obtained them "as found", missing bottom plates, mount hardware for the circuit boards, components, and with disconnected wiring. The selenium bias rectifier had been changed out for silicon, and the first B+ filter cap (made up from two separate caps connected in series) had been replaced likely previous to the amps being removed from original service (based on the style of caps installed). But the second filter caps (still in place) have failed with a very high power factor in both units, indicating that the amps were almost certainly taken out of service long ago. No doubt then, these amplifiers haven't seen AC power for decades.
My client got some really nice bottom plates made, and then sent the amps to me with the mandate to fully analyze them for any worthwhile modifications, and restoration for long term daily use. He also warned me that the engineer who started restoring them -- based on some previous gear he obtained from the man -- also had a habit of doing things uniquely "his way", which apparently produced some rather dubious returns, requiring further service for those earlier pieces. Sounds like a BOLO by any other name......
So, a few pics to get things started, and then I'll give my thoughts on where to go with these amps -- next time. Comments always welcomed.
Dave
Below: Yeah, let the drooling begin!
Below: I was going to tell the client that they were both junk, but I think I need to come up with a better story....... (black mark above the right rectifier tube of right unit is from some previous Duct Tape affair, but comes off easily enough)
Below: The undersides are a different story.....
And:
Below: But look a little closer at those new bias caps that were installed! Whoops........
And yet again..... (The ends you can't see are twisted together and grounded)
Below: I know. Tacky, tacky, tacky. But it did ultimately allow this unit to be rousted out of its slumber, and develop 60 watts RMS at 1 kHz from a 122 vac line, with the power transformer voltage tap set on 125 vac, using 6550C tubes. Bias and Balance controls were set to Fairchild specs. Amazing that those wax Good-All caps weren't leaking, as it biased and balanced easily -- although it wasn't really on long enough to find out if they were going to.......
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