Vintage Audio: A Pioneer SA-6500II Power Amplifier
Without a doubt, the best-known brand of hi-fi gear from the late ‘60s and throughout the ‘70s was Pioneer. The sleek styling of brushed aluminum panels and large illuminated dials convey a sense of sophisticated elegance that makes them sought after items even 40-some years after their manufacture.
Pioneer's product line always included everything from top-of-the-line equipment to gear that college students on a shoestring budget could afford. And sometimes there were package deals that included speakers, turntable, tuner, amp, and tape deck. This installment of Found in the Attic looks at a trio from the late 1970s – the SA-6500II power amplifier, TX-6500II AM-FM tuner and CT-F505 cassette deck.
The TX-6500 II was manufactured from 1976-78, and sold for $200. It was on the economy side of Pioneer's product line. All of these tuners had 3-gang tuning condensers and two ceramic filters.
Sensitivity was 1.9uV for FM, and 300uV for AM. FM selectivity was rated at 60dB, while AM was 35dB. Audio distortion was 0.6% for FM.
Typical of 1970s tuners, the back panel had terminals for both 300 and 75-ohm FM antennas, an AM longwire antenna, and ground. There was also a rotatable AM ferrite rod antenna, along with an FM de-emphasis slide switch to select either the conventional 75 us or long-forgotten 25 us Dolby de-emphasis. A front-panel switch enabled or disabled FM muting.
A conventional power supply delivered 6 and 7.5 VAC unregulated for the dial lights, and -1.4 VDC and 13 VDC regulated for the tuner. Semiconductors include one FET for the FM RF amp, three integrated circuits, seven transistors and nine diodes. The quality of construction is very good.
TX-6500s turn up regularly on eBay and other online auction sites. Since they were originally on the low end of Pioneer's tuner product line, they are less desirable items now than some of the high-end items, and prices of $15-20 are common. Items that have been refurbished and checked out can go for $65 or more.
The CT-F505 cassette deck dates from 1978, when the technology of tape and transports was well evolved, but hadn't yet reached its peak. Front panel switches selected either normal, ferric, or chrome bias, and switched the Dolby B noise reduction in or out. There was no Dolby C, automatic bias selection through cutouts on the cassette shell, auto-reverse, memory location storage, or return to zero.
It was late enough in the game, however, for manufacturers to be using plastic in the transports, as was the case with the pictured 505. That said, the fact that the transport works perfectly after 40 years speaks well for the quality of construction.
Of all the vintage stereo gear that surfaces for restoration, tape and cassette decks are the most difficult to bring 
back from the dead. Once the caps are replaced and the switch contacts are cleaned, you're sometimes left with transport parts that are made of unobtanium. A belt kit for the 505 is available from Vintage electronics, but that leaves the pinch roller, heads and assorted idler wheels. Other cassette and hifi parts can occasionally be found at Oak Tree Enterprises.
Repair of cassette motors can also be iffy. After the passing of 40 years, lubricating grease takes on the appearance and consistency of molasses. A good soaking in WD-40 usually takes care of this, and with repair of the PCB speed control, everything should be OK. Sometimes it isn't. The culprit can be the ferrite (powdered iron) material often used in armatures and field coils. Unlike iron or steel parts, ferrite can lose some of its magnetism after 40 years. Even NOS items that have been sitting on a shelf all these years can be worthless for the same reason. Sadly, this is unpredictable. Some ferrite motors still perform perfectly, while others of the same age do not.
A precise tune up also requires good alignment tapes. Reel tapes are easy to find, cassette, not so much. GennLab sells them for around $65.00 plus shipp
ng from New Zealand. A complete set would include standard level, Dolby calibration tone, head azimuth, and frequency response at various EQ settins.
The crown jewel of the trio is the SA-6500 II power amp. This amp is one up from the bottom of the line, but the Pioneer SA series had a well-deserved reputation for great sound. Specs were pretty good for 1978: power output 30 wpc; frequency response, 10Hz – 40 Khz; THD, 0.1%. Semiconductors included two integrated circuits, 25 transistors, and 16 diodes.
While this amp is in working condition and sounds OK, a full-force restoration might be in order. Many articles have been written about the 'sound' of passive components in hi-fi gear, and this is a subject unto itself. A rebuild would entail replacing all electrolytic caps, using bipolars where possible and substituting film or polypropylene caps for the ceramic di
scs. Many of the replacement transistors from ON Semiconductor or Fairchild can easily outperform the originals in the SA-6500. Metal film resistors have lower noise than carbon film, and in low-level circuits, can noticeably improve the noise floor. Once all of the desired components have been upgraded, an adjustment of idling current in the left and right power amplifiers would be in order.
This Pioneer trio was a gift from a friend who was moving. Unfortunately, they had been stored in a damp basement for many years, and the black metal covers are badly rusted in some places. (Note that these components also came in wood cabinets). There were very few scrathes or dings on the front panels, and they cleaned up nicely. All are in working condition, and still have a pretty decent sound, considering they have original caps and transistors. Service manuals are available for all three as free PDF downloads from HiFi Engine.
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