Loftin-White Telefunken Mono Amplifiers by James Burgess - RARE

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General:

These single-ended tube amps appear to have been built by James Burgess utilizing the Loftin-White design circuitry which uses the coveted Telefunken RL 12 T 15 from the 1930's. The driver tubes are PC86's and the rectifier in each amp is the Telefunken AZ-1.

All parts were considered when these amps were built and it is likely there are no upgrades to make them sound better. The transformers are very high grade O'Netics which cost about $1,400 by themselves.

The top surfaces are a copper color and the woodwork is beautiful showing appropriate aging and patina.

These amps put put 4-5 watts of single ended power which is surprisingly enough to drive most speakers over 99db in efficiency. Each amplifier is fitted with both 8 Ohm and 16 Ohm high quality speaker posts.

They sounded amazing powering our in-house Klipsch Heresy IV speakers to great levels, with top of class imaging and detail. 

Ownership:

Second Owner

Connections:

8 ohm and 16 ohm 5-way speaker binding posts. IEC power outlets. Standard RCA inputs. 

General Sound:

Neutral sound with little to no coloration 

Cosmetic Condition:

7 - Some Wear and Light Scratches

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Working Condition:

Working perfectly and tested in our lab.

Included:

Both amplifiers and installed tubes as pictured, and two power cords.

Packing:

Will be packed using our highly developed in-house process and custom packing materials.

Weight:

25 lbs. each

Age:

2000 

Recommended Cables:

Kimber Kable - RCA Interconnects - Better

Kimber Kable - RCA Interconnects - Best

Kimber Kable - Speaker Cables - Better

Kimber Summit Series Monocle XL Speaker Cables (PAIR) - Best

Kimber Summit Series BiFocal XL Bi-Wire Speaker Cables (PAIR) - Best If Applicable 

Kimber Kable - Power Cords - Better

Testing Process:

We start with a visual inspection of all internal components to make sure that there are no signs of heat stress or damage. Capacitors are checked for telltale signs of predictive failure including bulging, shrunken wrappers, or physical leakage. We also inspect resistors and other passive components for signs of overheating. If tube arcing has occurred in the past we can usually spot discoloration on the output tube sockets. On vintage units we often spot check select capacitors for value and ESR.

If the amplifier passes visual inspection, we move on to a full test of all of the tubes. We use an Amplitrex AT-1000 Tube Tester which is capable of testing both emission and Gm with a high degree of accuracy. We document the results of each tube and replace any weak or suspect tubes before proceeding. When we power on tube amplifiers for the first time we usually use a variac and current limited AC supply and slowly raise the voltage up to nominal mains level while monitoring plate, screen, filament, and negative bias supply voltages where applicable. If everything is in order we feed a low level test signal into the amplifier’s input and monitor its output on an oscilloscope across an 8 ohm dummy load. At this point we are just looking to verify basic function and confirm that the output transformers are not damaged. Once we have verified that the amplifier is safe to operate, we connected it to full mains power. For fixed bias amps we set the bias to manufacturer spec. For cathode biased amps we monitor the plate to cathode voltage to determine if the output tubes are operating in a safe range. Once the output section is verified we move onto bench evaluation.

We start by feeding the input of the amplifier with a low level 1KHz test signal, slowly increase its amplitude while monitoring the amplifier’s output on an oscilloscope for signs of noise, clipping, distortion, or improper channel balance. We continue increasing the signal level until the amplifier reaches clipping. At this point we take an output power measurement and compare it to the spec sheet of the amplifier to verify proper performance. We finish off the bench evaluation with a 1KHz square wave check and a 20Hz to 20KHz sine sweep to assess the amplifier’s frequency response characteristics. This battery of tests will usually reveal if the amplifier has any issues that need further attention.

Before the device leaves the bench, we perform a listening test with actual music using a variety of preferred test tracks. Our benches are outfitted with familiar monitor speakers which help us identify inconsistencies that will not always show up on our test gear. The main things that we are listening for are hum or noise with no signal present, proper center image, clicks, pops, or any other obvious undesirable audio characteristics.

If the unit passes all of these tests it is moved to our long term testing rig where we simulate real word operating conditions for 6-8 hours. For tube amps we like to run this test at least twice. This allows us to monitor the unit for signs of thermal runaway or intermittent issues that only crop up when it has fully come up to temperature. We find this step to be essential, especially for vintage units.