Pioneer SX-1250 Vintage Stereo Receiver - WOW For Sale

Pioneer SX-1250 Stereophonic Receiver

Description:

Back in the mid-seventies, if you wanted the most powerful receiver in the world, you had one choice - the Pioneer SX-1250. Introduced in 1976 at a retail price of $900 (over $3,700 in 2014 dollars!), the SX-1250 at 160 watts per channel was the second generation "monster receiver" offered by Pioneer, successor to the 110 watt per channel SX1010 first offered in 1974. In an escalating competition with Marantz, Sansui, and Kenwood for bragging rights as manufacturer of the world\'s most powerful receiver, Pioneer engineers spared no expense in designing an amazing piece of equipment that has become a legend among audiophiles worldwide - even to this day. In subsequent years, more powerful receivers have been constructed and marketed, but in my humble opinion, the SX-1250 outshines them all. Why?

It has one of the most robust power supplies ever incorporated into any receiver. The SX-1250 employs a huge dual secondary toroidal power transformer flanked by four massive, soup-can-sized filter capacitors to supply vast reserves of raw, ripple-free current. You need these current reserves to reproduce those bone-jarring musical peaks with perfect clarity, but having those huge filter caps also eliminates all traces of power supply hum and noise so during those subtle quiet passages, all you\'ll hear is the music.

It utilizes some of the best electronic shielding used in any vintage receiver. It\'s extremely difficult to keep a powerful receiver quiet. There\'s a lot of circuitry packed into that cabinet, all doing different things, not to mention powerful magnetic fields generated by the massive power transformer. Add to that, interference generated by electrical equipment and appliances in your house, and the typical receiver will pass some static, maybe some hum, maybe some spurious radio signals into the background when you\'re trying to listen to a quiet passage on a CD. Not the Pioneer SX-1250. Both of the super-noise-sensitive tuner circuit boards are built with metal boxes shielding them on all sides. Same for the tone control circuitry, and for the preamp circuitry and even the switching boards. In fact, when you pop the cover on this masterpiece, virtually all you see is metal. Literally no expense has been spared to ensure you have the cleanest, quietest backdrop to your musical experience.

You can still get all the parts! Most folks don\'t think about this, but if you want your investment to last, you want to make sure that it\'s built with the fewest obsolete parts as possible. This isn\'t always easy when it comes to vintage 38-year-old audio equipment. Believe it or not, the Pioneer SX-1250 contains no parts that can\'t still be obtained new, or at least be replaced with new cross-referenced parts today. Well, okay, maybe the big power transformer would be tough to find, but I\'ve never ever heard of a Pioneer toroidal power transformer going \'south\', nor have I heard of anyone else who has. This unit uses no unobtainable dual-section filter caps, no obsolete RET, VFET, or flat-pack output devices, nor any "unobtanium" proprietary tuner ICs used in many subsequent monster receivers.

The bottom line is simply that the Pioneer SX-1250 represents arguably the best value in a high-power vintage receiver today, bar none. Back in \'76, The Pioneer corporation engineered and built what was then, simply the finest receiver in the world. In the humble opinion of a guy who\'s been working on and enjoying vintage audio gear since the early \'70\'s, it\'s still the best of the best.

Condition:

Cosmetically, after taking everything into consideration, this unit is truly in outstanding condition - not perfect, mind you, but all imperfections are quite minor and require close inspection to even notice. The walnut-veneered cabinet: Very nice, with some minor wear discernible, but you really have to do a close inspection to see it. There is a small shallow dent on the top-facing surfase, and very minor chipping of veneer on some of the lower edges and on one corner. The front walnut faceplate strips are excellent. The faceplate and chassis: Very, very nice - a small nick on the upper edge of the faceplate is the only issue worthy of mention - yoiu can just barely see it in the photos. The top-facing edge of the metal faceplate on these receivers is usually pretty badly scratched up, but not on this one - it\'s almost perfect (see pics). There is no corrosion anywhere on this unit - even the interior sparkles with mint-sheen. The AM rod antenna, broken on many of these classic Pioneers, is in place and adjusts properly throughout its travel. The original factory preamp to amp jumpers are also present, as are the original padded feet.

Functionally, this receiver is without question a 10 out of 10 - and very possibly better. It\'s been thoroughly and completely restored, including a full power supply board rebuild, a complete electrolytic capacitor replacement, a conversion of indicator lamps to LEDs, and much, much more (for full details of all restoration services performed, please see below.) All controls work smoothly and are completely noise-free as are all lever and pushbutton switches. The FM section has been meticulously aligned and is unbelievably sensitive, not only pulling in my rural FM stations in stereo without any antenna connected, but pegging the signal strength meter when using only an 18" wire (that\'s what I used to take the pictures)! Finally, the amp - channels well-balanced, nice and quiet at idle, with no hum or abnormal noise in either channel, and enough power to really blow your hair back. The original factory-matched driver and output transistors are present and healthy, so that wonderful Pioneer sound remains uncompromised. This receiver simply performs magnificently all around. If you\'re looking for a top-notch \'70\'s receiver literally built to last a lifetime, you could easily spend hundreds more, but you simply won\'t find a better looking, better built, or better performing example than this beautiful Pioneer SX-1250.

Photos: (Quite a few - please allow time to load...)

Some shots of the interior. Note the presence of metal shielding everywhere. Even the foil sides of the four vertically-mounted rear circuit boards are all shielded. As a result, all hum and external interference is completely eliminated from the signal line.

Restoration Notes:

Here are all the new parts that will eventually go into this receiver. Let\'s get started!

Here\'s a photo of the regulated power supply board before reconditioning. If the SX-1250 can be said to have any design weakness at all, it would be this board. It\'s mounted vertically in the receiver to create a "chimney" effect, so that it can be convectively cooled by rising heat currents. Nevertheless, it still gets extremely hot - particularly if the receiver is operated in a cabinet or other enclosed environment. Heat kills electronic components, and those on this board are usually the first to go. The same board, after restoration. All electrolytic capacitors have been replaced with brand new high-temperature equivalents, most rated to 105°C (221°F) - as compared to only 85°C (185°F) for the originals. All transistors have been replaced, most of them with larger, higher current-capable devices. All diodes, including zeners, were also replaced, and the old trim pots were upgraded to new Bourns precision trimmers., and the old trim pots were upgraded to new Bourns precision trimmers. And that\'s just the top side of the board!

This is the foil side of the un-restored regulated power supply board, illustrating the disastrous effect of high heat on solder joints. Each yellow arrow is pointing to a potentially compromised solder joint, identified by a circular "ring crack" surrounding the wire. These little rings, caused by the differing heat expansion coefficients between the wire and the solder, eventually lead to intermittent connections - and ultimately to the failure of the receiver. Here\'s the same board, after a proper reflowing of all solder joints and a good cleaning (the yellow box outlines the area shown on the previous photo). Good, long-lasting solder joints should be well-domed and shiny. Top-quality Kester brand silver-bearing solder was used to refresh the joints on this board, and for all other solder work done on this receiver.

38 years can really build up some serious oxidation on silver-coated copper connecting pins, and Pioneer used dozens of them for the plug-in circuit boards on this receiver. Since dirty, oxidized connecting pins are at the root of many maladies plaguing old vintage receivers, a through cleaning of each and every one is in order.

This is the protection board, prior to restoration. This board contains circuitry that, among other things, protects your speakers by disconnecting the receiver from them in the event of a fault. Obviously, it\'s a good idea to ensure this speaker protection circuitry is in tip-top shape. In addition to replacing all electrolytic capacitors on this board, all transistors in the protection relay circuit with brand were replaced with new, beefier ones designed to handle more current and more heat. Finally, rather than simply cleaning the contacts of the old relay, a brand new replacement is installed.

Here\'s the fused power board, before and after "recapping". Note that the replacement capacitors are significantly smaller than the old ones. This is due to advances in capacitor design and manufacturing over the past several decades, which allow new devices to provide the same performance in less than half the space.

Here\'s the chassis, after being stripped down and thoroughly cleaned. This is a VERY well-preserved receiver - not a spot of corrosion anywhere! The old filter capacitors (left) compared with the new. In addition to refreshing the tired, 38-year-old filters, the new ones can handle 25% higher working voltage AND also have the ability to withstand higher temperatures.

Here, we\'re testing the old filter capacitors. Originally rated at 22,000µF, this particular filter has lost almost 20% of its ability to store a charge. The other three weren\'t much better. Just to confirm the new filter capacitors were \'up to snuff\', they were subjected to the same testing as the old ones. As expected, all of the new filters tested at or above their rated capacitance.

This is the tone amp board, prior to "recapping". The small blue oval-shaped devices are tantalum capacitors, very popular in the \'70\'s due to their relatively high capacitance, durability, and small form factor. Today however, many audiophiles maintain that tantalum capacitors, when used in the signal path, impart a harshness to the sound. Moreover, when tantalum caps do fail, they tend to short-circuit, which can lead to receiver damage. A good restoration, therefore, includes replacement of all tantalum capacitors along with the more common cylindrical electrolytic capacitors. And, the tone amp, after recapping. All capacitors in the signal path here, and on all other boards in this receiver, have been replaced with top-quality audio-grade Nichicon "UKW" series components. By the way, as the transistors on this board are known to cause noise troubles, they have been preemptively replaced with modern low-noise Fairchild equivalents. All potentiometers and switches have been thoroughly cleaned and preserved with professional-grade Caig products (Deoxit, Faderlube, etc.).

This is the \'flat amp\' board, prior to restoration. In addition to electrolytic & tantalum capacitor replacement, the all controls and switches have been thoroughly cleaned and preserved with Caig Deoxit products. The volume control requires special treatment, however... The volume control in this receiver is actually a \'stepped attenuator\' of sealed design, and therefore must be desoldered and disassembled to be properly cleaned and deoxidized. The control was thoroughly flushed with Caig Deoxit D5 cleaner, blown out with compressed air, and then lubricated with Caig Faderlube F5. As a result, the volume control now operates like new - with absolutely no noise or scratchiness.

And, since the balance control on the flat amp board is mounted such that it\'s almost impossible to get cleaning fluid into it, it was removed for a thorough, proper cleaning. The flat amp board, completely restored, and ready for the next 38 years!

The phono amplifier board, before and after restoration. Several tantalum caps were replaced here as well.

The left channel power amplifier board, in its original state. Not too bad, actually- a bit dusty, but like the right channel board, all original, and never serviced. Both power amp boards receive all-new caps, and new Bourns trimmer resistors (the blue boxes). The DC offset trimmer has been upgraded to a 12-turn type, which makes it much, much easier to zero out DC on the speakers, which is done later. In addition, the large heat-sinked driver transistors are removed, cleaned, and remounted with new mica insulators and fresh thermal compound. Finally, the connecting pins are all burnished and all solder joints on the back side are carefully inspected and reflowed as needed.

Here\'s an excellent example of why a good restoration includes removing, cleaning and remounting all heat-sinked transistors. The white crumbly material below started its life as thermal transfer compound, a grease-like material designed to help its transistor "off-load" the considerable heat it generated to the larger metal heat sink. Over time though, this heat transfer compound breaks down, and can actually become an impediment to good heat transfer. The transistor and heat sink are cleaned, and fresh thermal transfer compound is applied to a new mica insulator and to the cleaned transistor. Technique is important here as well - too much or too little thermal compound can actually be an impediment to optimal heat transfer. A thin, slightly translucent coating is what we\'re after.

And here we have the tuner/MPX board, before and after. Most folks who do vintage restoration work shy away from replacing tuner circuitry capacitors, citing fears that it would negatively affect the receiver\'s tuner alignment. In my experience though, I find that the exact opposite is true. While this receiver\'s tuner section performed admirably prior to restoration, afterwards, its performance was astonishing. I normally do a complete FM realignment as part of my vintage restorations, but with this receiver, there was no point - since recapping, it now has one of the most sensitive and well-aligned tuners I\'ve ever seen. Remarkable.

No worthy tuner restoration is complete without a thorough cleaning of the variable tuning capacitor. The central spindle\'s bearings and sleeves are carefully cleaned with Deoxit to improve contact to the capacitor\'s outer metal housing. This maximizes sensitivity while eliminating tuning noise. Note the quality of the SX-1250\'s tuning cap - five gangs for FM and three for AM. More tuning gangs generally equals better sensitivity and sensitivity, and the tuner in the SX-1250 is one of the best in any receiver. Rounding out the tuner servicing is a complete disassembly, degreasing and re-lubrication of the main tuning bearing. Of the years, the factory lubricant turns into a sticky sludge, and it takes several twists to get the tuning needle across the dial. Deoxit was used to clean out the old grease, and top-quality synthetic lube was used to replace it. Now, the tuning needle can be sent from 88MHz to 108MHz with one quick twist!

The big power transistors all receive a fresh coat of thermal transfer compound, and are remounted using brand new mica insulators. All heat-sink mounted transistors in the receiver get the same treatment. This keeps these high-current devices running as cool and efficiently as possible. Before reinstallation, the pins of all eight output transistors are thoroughly cleaned to ensure the best possible contact.

Here, all of the output transistors have been remounted. This receiver has all of its original factory-matched driver and output transistors in place, another indicator that the original owner took very good care of it.

Here\'s a shot of the function indicator lamp assembly, showing the original incandescent bulbs. On a typical vintage Pioneer receiver with average use, the beige rubber shroud is normally hardened and discolored from the constant heat of these bulbs. This one is soft and pliant, with no heat damage at all - another indicator of "very low miles" on this particular SX-1250. All the incandescent function indicator bulbs have been replaced with warm-white 5mm LEDs, shown here with their associated current limiting resistors. These LEDs generate next to no heat, use a fraction of the energy used by the original bulbs, and have an approximate 100,000 hour lifespan. As a result of this upgrade, you will NEVER have a function indicator burn out in this receiver. Period.

The first function LED has been replaced. The black sleeving is unshrunk shrink wrap that will eventually be heated to snugly fit over the current limiting resistor inside. Only eight more to go! LED conversion has been completed, and all LEDs have been neatly remounted behind their indicator lenses.

Setting up for final adjustment and testing. Yep - that\'s my kitchen table (I have a VERY understanding wife!). The green cylinders behind the receiver are large load resistors - we\'ll need these for accurately testing power output. Dialing in the regulated supply voltage to an exact ±65 VDC, as specified in the service manual. Getting this voltage correct is important, as it feeds most of the circuitry in the receiver.

Zeroing out any DC voltage on the speaker terminals. DC on your outputs is bad, as it can cause distortion in small amounts, and damage your speakers in large amounts. Getting within a few millivolts of zero is great. This receiver can be zeroed under one millivolt on each channel. Bottom line, this is a very healthy, stable receiver. After warming up, the idle current can be dialed in within a few tenths of a millivolt to the factory spec of 100 mV. (Generally, a 10% variation is acceptable, so you can get an idea of just how stable the output circuitry on this receiver really is!) "Idle current" (a.k.a. "bias current") is a small amount of electric current supplied to the output transistors to ensure that they never completely shut off. Getting it properly adjusted is important - if it\'s set too low, sound quality can become harsh due to \'switching distortion\'. If it\'s set too high, the the output transistors run too hot and can become damaged.

Okay, now that we\'ve put so much time and effort into getting this ol\' girl back in tip-top shape, let\'s find out what she\'s really got under the hood. We\'re testing the SX-1250\'s power output just before clipping, with both channels driven into 8-Ohm load resistors. Notice the nice clean 1 KHz traces on the scope for both channels, just slightly offset from each other so you can confirm matching amplitude. You can see 38.07 VAC on the right true RMS voltmeter - right channel power output = E2/R = 1449.3 ÷ 8 = 181 Watts. Left channel measured 182 Watts. Definitely some power to spare, but wait..... And now... the "acid" test. I generally don\'t run 4-Ohm bench tests, because there aren\'t too many amplifiers designed to handle such a low load impedance (you subject a receiver to a 4-Ohm load whenever you hook up two sets of 8-Ohm speakers and run all four at once). Unlike some of their later models, Pioneer actually provides specifications for the SX-1250 into a 4-Ohm load, so they obviously felt confident that this receiver could handle it. For each channel, two 8-Ohm load resistors are connected in parallel to yield 4-Ohm loads, and the same 1kHz tone is amplified until just before the waveform on the oscilloscope begins to distort. Checking the left channel, P = E2/R = (31.76 x 31.76) ÷ 4 = 252 Watts. Right channel comes in at 253 Watts. I guess Pioneer\'s rating of 200 Watts into a 4-Ohm load is rather conservative, eh?

A shot of the included literature. The owner\'s manual, fold-out schematic diagram, and warranty literature are originals, the rest are high-quality color laser copies.

Finally, a shot of all of the original parts that have been replaced in this restoration. The winning buyer is welcome to these at his/her option - please let me know after the sale.

Restoration Services Provided:

• All electrolytic and tantalum capacitors on all boards (including tuner board) replaced with brand new components:
  • All electrolytic caps in signal path replaced with Nichicon Audio Grade "UKW" series
  • All electrolytic caps in power supply and smoothing applications replaced with Nichicon 105°C Hi-Temp "UPW" series
  • Original 22,000 µf 80V 85°C filter caps replaced with brand new Nippon Chemicon 22,000 µf 100V 95°C
  • All small electrolytic caps (less than 2 µf) replaced with new Panasonic polypropylene capacitors
• All transistors and diodes replaced on critical regulated power supply circuit board
• Bias, offset, and regulated supply trimmer resistors replaced with new Bourns equivalents
• Trouble-prone 2SA725, 2SC1313, and 2SC1312 preamp transistors replaced with modern low-noise equivalents
• Speaker protection relay replaced with new Omron equivalent
• Protection circuit driver transistors replaced with more robust devices
• Incandescent dial lamps replaced with brand-new 8V 250 mA long-life bulbs
• All incandescent function indicator lamps replaced with long-life (100,000 hour) LED devices
• Regulated power supply adjusted to exact factory spec (65VDC)
• DC offsets zeroed and idle currents set to spec (100mA), after one hour warm up/stabilization period
• All rotary potentiometers cleaned with Caig Deoxit G5 and lubricated with Caig Faderlube F5
  • Sealed volume attenuator desoldered, disassembled, cleaned and lubed as above, reinstalled
  • Difficult-to-clean balance potentiometer desoldered, cleaned and lubed as above, reinstalled
• All rotary and pushbutton switches cleaned with Caig Deoxit G5 and preserved with Caig DeOxit D5 Gold
• All heat-sink-mounted driver and output transistors removed, cleaned, and remounted with fresh thermal transfer compound and new mica insulators
• Tuning capacitor bearings cleaned and lubricated, main tuning knob bearing and all dial string pulleys lubricated
• All RCA-style inputs, dubbing jacks and headphone jack internally and externally cleaned and deoxidized
• Discriminator touch-up alignment performed
• Dial pointer precisely calibrated via local oscillator touch-up
• Chassis and all circuit boards cleaned; all plug-in connecting pins burnished
• Silver-bearing solder used in all replacements, and to reflow any other suspect joints
• ONE YEAR full parts and labor warranty included *

What You Get:

• Pioneer SX-1250 receiver, serial #XK3628817S, manufactured in November, 1977
• Original SX-1250 Handbook of Instructions
• Original foldout schematic of the SX-1250
• Original Pioneer warranty card and dealer listing
• Full color high resolution duplexed copy of full service manual for the SX-1250
• Color laser copy of five-page detailed promotional brochure for the SX-1250
• Full listing of all parts used in this restoration, including supplier part numbers and restoration notes
• All old removed parts (optional - please let me know if you want these)

Features:

• 160 watts per channel at 8 ohms, 200 watts per channel into 4 ohms!
• Power In and Pre Out jacks allow unit to be used with separate preamp or power amp
• 30Hz & 8kHz tone filters for ultra clean low and high ranges
• Dual bass controls (50Hz and 100Hz) for precision low frequency control
• Dual treble controls (10kHz and 20kHz) for precision high frequency control
• Tone defeat switch for the purest, most accurate reproduction of any source material
• Three separate speaker outputs, any two of which may be used together
• Numerous Inputs - Phono 1, Phono 2/Mic, AUX, Tape 1, and Tape 2, and \'Adaptor loop\' (can be used as Tape 3!)
• Signal Strength & Tuning Meters for ultimate reception of AM & FM bands
• -20 dB audio muting switch - perfect when the phone rings!
• 25µS / 50µS / 75µS rear panel FM De-emphasis switch
• FM Multipath button
• FM Muting button
• Three rear accessory outlets
• And more...

Specifications:

Power Output: 160 watts per channel RMS into 8 ohms, 200 watts per channel into 4 ohms, 20 Hz to 20 KHz Harmonic Distortion: Less than 0.1% at full rated power into 8 or 4 ohms, no more than 0.05% at 80 watts/channel Intermodulation Distortion: Less than 0.1% at full rated power into 8 or 4 ohms, no more than 0.05% at 80 watts/channel Frequency Response: 5 Hz to 100 kHz, + 0 dB, - 1 dB Hum & Noise: 100dB FM Sensitivity: 1.5µV FM Capture Ratio: 1.0 dB FM Harmonic Distortion Mono: Less than 0.10% @ 1kHz FM Harmonic Distortion Stereo: Less than 0.25% @ 1kHz Damping Factor at load impedance: 30, 20 Hz to 20 kHz into 8 ohms Dimensions (W" x H" x D"): 21-7/8 x 7-3/8 x 18 -1/4 Weight (Unpacked): 64.3 lbs.

Terms:

If you are not 100% satisfied with this unit, you may return it within 14 days of receipt for a full refund of your purchase price and original outbound shipping (yes, return shipping would be your responsibility). Full refund would of course be contingent upon receiving the returned unit in the same condition in which it was sent, without any missing or exchanged parts.

*As most failure-prone parts in this receiver have already been replaced, I am happy to offer a full one year warranty on this unit. Should you have any problems within one year of receiving this item, I will repair it free of charge, including parts and labor, provided you handle round-trip shipping.

Due to guidelines, I accept only PayPal payment. Buyer pays fixed FedEx Ground shipping rate of $75.00, which includes shipping insurance and absolutely bulletproof packaging, for any destination in the continental US. Buyer MUST respond within 3 days of the sale end or transaction will be void. Payment MUST be received within 10 days of the end of the sale or the transaction will be void. I reserve the right to cancel offers from any party with a response rating at or below zero, or any party with excessive negative response. Good luck and happy offerding!