Saturday, September 26, 2009

The Pioneer SX 1250 Receiver

The Pioneer SX 1250 is one serious, high quality electronic monster. Sold from '77 to '79, it was Pioneer's top of the line receiver and boasted 160 watts per channel in a sixty pound chassis. The build quality is very high and properly restored they sound great. Not all of the late '70s monster amps and receivers sound great, but the SX 1250 truly does. I restored one about 6 months ago and neglected to write it up at the time, but it recently wandered back into my life due to a problem.

This unit's original problem was two blown main filter caps. My original thought was it was just time for the caps to go, now 30 years old, but the restoration revealed problems on the regulator card. Someone had previously done a completely inadequate repair and that card required replacement of pretty much every component, active and passive. Poor voltage control could have been a contributing factor in the death of the main filters. A 1250 deserves quality parts and someone didn't give this receiver the respect it deserved.

I replaced all 4 main filters with lovely Hitachis and recapped all 4 vertically mounted cards, the AC relay board underneath, the phono section, and the preamp cards behind the face. The two relays were burnished and all the pots and switches were squirted. The post restoration listening was a total pleasure.

Time passed and the unit ended up back at Mike's for resale. Mike set it up for a listen and proceeded to punch all its buttons. I confess I never use most of the tone controls on my receivers and I must have missed testing the two high cut filter switches towards the left side of the front panel, just above the bass and treble pots. When Mike clicked them there was a significant pop in the left channel, so it was time to peel the face again and make it right.

These two filter switches sit on their own board above the tone control board which needs to be removed for access. It had been pulled to spritz the switches with blue foam and deoxit, but no components had been replaced in the original restoration since it only had two small transistors, 4 tantalum caps and a few film and ceramic caps. These components are not typically points of failure, but 'typically' is not exactly 'ever'. Mike's estimated order of likely offenders was transistors, then tantalums and then the ceramics. Mike checked them all out in circuit and all seemed normal.

Mike swapped the transistors and the offending pop was still there.



Next up were the 4 relatively low voltage blue egg tantalums, at 4.7mfd and 10mfd, and that solved the problem.


Here is the modified board with two new transistors and 4 electrolytics replacing the tantalums:


The SX 1250 was reassembled and Patricia Barber spun on the highly tweaked Samsung DVD player with very impressive results. The SX 1250 is a head turner, one of those amps that sound good enough in the next room to drag you in for a listen. It even sounds great on Mike's beloved Infinity Quantum 2's that can get very agressive with many amplifiers. It takes an amp with considerable low end control and weight to balance out the 3 emit tweeters on the front.


It's a great looking piece of gear for those with a strong back, a very heavy duty shelf and a taste for the top of the line. It's a great representative of the very best Japanese solid state engineering in the '70s.

13 comments:

David Wood said...

I have had an SX1010 for 25 years. it finally bit the dust. I picked up on of these 1250 units in very pretty condition. Said to be working, but no sound output.... I,m having a sad SX year.

regards

d.wood

Nat said...

David: Is DR5 linked to your name your business? Very nice.

The big Pioneers are well worth restoring, but, sadly, all the big silver amps and receivers are at the end of their first lives. In truth they have not been at their best for a while. But they can be restored to better than new for another 20-30 years of enjoyment. Find a responsible tech who will do it right. Recap it all with quality caps. The voltage regulator card needs special attention. If you want it to sound right the preamp boards behind the face need to be restored.

This is not cheap but this gear deserves to live.

Nat

kelsci said...

One of the great stereo receivers of all time.

chrislohrcdm said...

I have one of these and love it. Last night I had it on and heard a pop in the middle of listening to a radio station program and then there was no sound. When I went into the living room to see what was going on there was no sound and a little white smoke coming out the right side grille. Any advice?
Thank you!
Chris

Nat said...

Chris: smoke is never good news with electronics, especially with a 1250. The caps in these amps are failing. It has been 30 years and their time is up.

Put the 1250 on its back and remove the bottom cover. Unplugged, of course. If you see a bit of a mess on the inside of the bottom cover that means one or more of your 4 main filter caps (the soup cans!)just vented its life away.

Maybe the point of failure was the can itself, but often it is the fault of the voltage regulator card, one of the 4 vertically mounted cards accessible from the top. A cap can fail here, the voltage runs away and takes out lots of things, including one or more main filter caps downstream.

The bad news is the cap that failed is just the first of many that will fail over then next few years, assuming it is all original. The good news is these amps can be restored to typically better than factory electrical condition.

Restoration is expensive, but it will sound great, and it will last another 20-30 years.

Good luck.
Nat

Alan said...

I have one of these SX-1250 and I'm looking for a "reliable" repair facility and/or person I can send it to and get it brought back to life.

It worked great for a long time, but then I let it set for a few years without use. Recently I moved it to a new location so I can use it again, hooked it all up, turned it on, worked for 45 seconds, then no more sound. Turned it off, waited a few minutes and then turned it back on; it worked for about 15 seconds then went out again. Strange.

I really enjoy the sound this unit gives and would like to get it working again, but I don't know of any reliable place to have it repaired.

Can anyone recommend someone or someplace that works on these units?

Thank you,

Alan

The Pocono PC Doctor said...

I have an SX 1250 - needs repair, as one channel works for a while and then cuts out. You mention a "Mike" person in your post.

Does Mike do repairs from out of state? Or do you know another source to fix the SC 1250's?

Thanks for your help, and I ma still checking the links, but they seem to be for parts, not repair.

Nat said...

This blog is not intended to be an endorsement of Austin Stereo Service, but... I confess the reason I hang out there so much is Mike Manulik and Robert Cooley are experts on this stuff that I love. Each has roughly 30 years of experience in repair and restoration of electronics. I paid for their services for about 15 years and finally Mike told me it was time I started doing it myself. So I did.

The number for Austin Stereo Service is: 512.451.0408. I recommend Mike and Robert without reservation. They are honest and extremely knowledgeable. Mike handles vintage solid state and tube gear. He restores lots of Mac gear, including that of one of our local guitar geniuses. Robert does solid state restorations, including reel to reels and keyboards. He worked on my Moog Sonic Six a few years back.

Now for the caveats:

1) Shipping for heavy electronics is expensive, and you will have to pay for a round trip.

2) Pack your gear well. No, 'well' is not good enough. Make it bullet proof. Check out my write up on swim noodles. They are a buck apiece at Dollar Tree, so there is no excuse for crappy packing.

3) Mike will not want to repair your vintage piece, he will want to restore it. He will refuse to chase a problem in a 30 year old component. All the caps are drifting or gone. The guy who fixed it 10 years ago might have been a hack. It might have been running for the last 5 years with out of spec voltages. The point is Mike cannot guarantee a blow out patch, but he will stand behind a restoration.

4) Restoration will be expensive.

Ok, so what constitutes a restoration? At a minimum, Mike will replace every cap in the power supply, the driver boards, and the preamp. Restoration of the phono and tuner sections is at your discretion (but I think it is nuts not to do them). Depending on the situation a restoration can extend to active components like the low noise high gain transistors in the preamp. Relays are always burnished (worth an article itself) and the pots and switches are cleaned. The unit is burned in for a few days and then Mike will pack it and ship it back.

Mike has done lots of Pioneer solid state, including all the large receivers and the Spec series of separates. He has restored many a Fisher, Scott or Mac tube component. He can handle oddball items.

I can rattle on, but if you have a need, give him a call.

The Pocono PC Doctor said...

Wow, thanks for the information. Understood about the costs of shipping.

Hopefully I can fit the restoration in my budget.

Candy99Tx said...

Thanks, Nat, for the repair info.....I just called and talked to Mike and will be planning a trip to Austin to have him (Robert) repair my SX-1250. I am really excited to have my baby working again...it is such an awesome amp....I have a Marantz 6100 TT, and 2 chest high disco speakers that I bought back in the day as a whole system....can't wait until it's all back together and working again....woohooooo!

Anonymous said...

I owned an SX-1250 from 1978 till 1991. I originally bought it in Rochester, NY and moved to San Diego in 1979. It played through Altec Lansing spkrs up till 1990, when I bought a pair of Klipsch Forte II's. It always sounded awesome and could punch out loud, clean dynamics easily. I do remember a small plume of smoke near the end of ownership. I had it repaired, but I don't recall what failed. I sold it for $200 in1991. I miss its looks and sound, but not its weight. - Jack in San Diego.

Electronics and home theater equipment said...

I bought this Pioneer SX Surround sound receiver. Since I am not very demanding in my sound needs, this set was perfect for me. They're a lot better than the speakers on my monitor that I had been using, that's for sure.
Thanks for the post.

Anonymous said...

The SX-1250 is famous for those little 3 legged transistors failing. Any corrosion on the legs works it way up and the transistor fails. Replacements are dirt cheap and far better than the originals. There are a handful of these little transistors thruout the unit. Replace them all. Anyone who has heard a pop, crackle etc ... this is likely the culprit. Of course, failed parts often mean its time to fully recap and restore. Electronics 30 years old will fail .. FOR SURE. I've had many Pioneers including the 1250. There is no comparison to original vintage and after restoration. You do not know what it sounds like until you restore it back to fresh factory spec. I assure you this. Yet so many people just buy a used piece and hope for the best. That will not give you the real picture or experience.