I was reminded of that episode a few weeks ago, when a friend called to say he had just finished repairing a client's Marantz Model 8B amplifier: If I wished, and if I promised to be careful, I could borrow it for a day, before it had to go back. Again, I jumped at the chance. Again, the results are less than biblicalalthough this subject was more agreeable.
I have a reputation, I suppose, for regarding vintage audio gear in a favorable light. I would hope that I'm also known for candorand candor compels me to say that the 8B, though lovely, was bettered by more than one contemporary amp of my acquaintance. The Marantz sounded colorful and well textured, but no more so than at least a half-dozen modern amps, which also manage to sound more extended and, above all, faster. By comparison, that old 8B sounded . . . well, it sounded just a little bit old.
But I digress . . .
The Marantz Model 8 stereo amplifier made its debut in 1959, not long after the Model 7 preamplifier was introduced, and just one year before the Model 9 monophonic amplifier. Sidney Smith, who designed the 8, the 9, and various other classic Marantz products, eventually departed from numerical order just long enough to revise the Model 8, endowing it with upgraded output transformers of his own design and a sophisticated global feedback system. The resulting amp, the Model 8B, was first offered for sale in 1961 or '62, for the then-considerable sum of $250.
The 8B has two complementary pairs of EL34 power pentode tubes, operated in a class-A/B, Ultralinear output circuit. The amp is a fixed-bias design, and its top panel is adorned with a meter, a rotary selector switch, and four trim pots, all used to facilitate bias adjustments. Each channel has its own 6BH6 pentode, for voltage gain, and 6CG7 dual-triode tube as a phase inverter. The main power supply is rectified by four rugged if not quite immortal silicon diodes, with a selenium rectifier stack for the bias supply. Output power is specified as 35Wpc.
The Marantz 8B uses up to 20dB of global feedback, and it is there that Sidney Smith's design becomes especially interesting. First, the frequency range over which the maximum feedback is applied can be fine-tuned by adjusting a trim cap in each channel's feedback circuit. Second, the feedback signal for each channel is taken not from the secondary tied to the loudspeaker outputs, but from an extra pair of secondary windings that were intended specifically for the job.
In addition to the extra secondary windings, each of the 8B's output transformers has an extra primary; each is isolated from the other and dedicated to a single EL34 tube. With the amplifier's top-panel rotary switch set to Normal, the B+ (ca 435V) is applied equally to those four separate primaries; during bias adjustment, when the switch is used to select among the four individual tubes, the full B+ is applied to just one transformer primary at a timebut this time through the meter and its shunt resistor. (The former reads voltage drop across the latter.) Thanks to Smith's clever transformer design, Marantz could commend the Model 8B for use in either Ultralinear or triode mode, the latter effected with a few minor wiring changes. Given that each output tube had its own primary, there's no reason this amp couldn't also be adapted to single-ended operation, with either one or two output devices per side. But let's not do that today.
A final bit of electronic filigree: Inside the chassis there's also a pair of trim pots for adjusting the symmetry of the waveform produced by the 6CG7 phase-splitter tubes. Like the trim caps for the feedback circuit, those adjustments weren't intended for the casual user. What a mercy!
Appearances aren't always deceiving
As suggested above, the Marantz I borrowed needed a little work. One resistor had to be replaced, as did the four silicon diodes comprising the rectifier for the main supply. On the other hand, not a single one of the original capacitors was in obvious need of replacingremarkable for a 50-year-old amplifier.
This amp's most grievous flaws were cosmetic, themselves the apparent result of careless storage. (Other Marantz 8Bs of my acquaintance, such as the one owned by the late Edison Price, appeared evergreen.) The EIA codes stamped onto the bias potentiometers indicated that those parts were manufactured in 1964; while hardly conclusive, that suggests that this 8B is from 1964 or 1965.
I hefted the 56-lb Marantz onto my equipment rack and connected it to my usual system, with spade-lug-to-banana adapters between my Auditorium 23 speaker cables and the 8B's rear-mounted terminal strip. Through its normal input jacks (the amp is also equipped with a pair of test inputs, bypassing the sub-20kHz rumble filter), the Model 8B exhibited not a trace of hum, and produced only a small amount of steady-state hiss at idle.
Music sounded pleasantly thick, stringy, and colorful through the 8B. Electric basses in most rock fare, such as "Cinnamon Girl," from Neil Young's Everybody Knows This Is Nowhere (LP, Reprise 6349), were sufficiently full but loosey-goosey in the timing department. Imprecise note attacks, more than excessive overhang, were the culprits. A Naim 250 this was not.
Detail and openness were acceptably good, making it easy to tell Young's guitar playing from that of Danny Whittena distinction beyond the abilities of lesser antiques. Interestingly, with that Neil Young record and others, the Marantz did something I've come to associate with various products that don't suffer from a lack of character: It had a knack for calling my attention to elements of music that don't always come to the fore. Some instrumental solos faded into the background, while other detailspercussion and, especially, backing vocalscame way to the front. The phenomenon may be down to nothing more than minor frequency-response aberrations, so I hesitate to make it down to anything terribly mystical. But still . . . !