JBL 6010B (circa 1975)

The 6010B is a professional series monaural power amplifier. It's a rack-mounting workhorse from around 1975, sold in Japan at ¥246,000 per unit. It's a pro-audio piece, not a home hi-fi amp. JBL rated it at 100W RMS from 40 Hz to 12 kHz, delivered through a built-in output transformer with 8Ω, 16Ω and 70.7V taps. A bypass circuit allows direct 4Ω operation for studio work where bandwidth and distortion matter more than the transformer's line-driving flexibility. The standard input is unbalanced 50kΩ. It converts to balanced (15kΩ bridging or 600Ω matching) with the accessory 5195 transformer. A rear-panel switch engages a 250 Hz low-cut filter, which the manual says reduces the possibility of damaging horns. The front panel is dark gray semi-gloss baked enamel, and the unit takes up five EIA rack spaces and weighs 21 kg.

JBL's own literature leans hard on reliability. The protective circuit is described as making the amplifier "virtually impossible to damage" under overload, shorted or mismatched loads, and excessive input. A thermal switch trips if the heat sink passes 200°F, and the DC fuse guards the power supply specifically against output-stage failure. The manual also claims the amp can be overdriven by at least ten times normal input voltage from 40 Hz to 12 kHz, producing square waves up to roughly 160W RMS before output begins to fall. It also claims the amp draws only about 30% more AC power at 12 kHz/100W than at 1 kHz for at least an hour without entering "protect." Those are manufacturer claims, not independent measurements. No period review of the 6010B survives in the archive.

Several things are thin: production years beyond the circa-1975 price reference, any confirmed price outside Japan, damping factor, and any current market or failure data. The service manual survives only as a scanned three-page schematic PDF (about 1.8 MB). The few third-party listings are manual-download mirrors repeating JBL's own boilerplate.

Known specifications:

Rated output: 100W RMS, 40 Hz – 12 kHz
Rated input: 0.7V
THD: 1.0% or less at rated output
Intermodulation distortion: 2% or less at 100W; under 1% at 10W; 1% or less at 0.15W
S/N: 85 dB or better at 100W or less
Outputs: 8Ω, 16Ω, 70.7V transformer taps; 4Ω direct bypass
Dimensions: 483 × 222 × 295 mm (W×H×D); 21 kg
Rack size: 5 EIA spaces