New to vintage audio. Looking for some tips.

[Spin_Vinyl]

Howdy all. I recently scored a Pioneer SX-780 for dirt cheap. ($40 to be exact).
I have dusted it out, cleaned all the POTS/switches with De-Ox-It, replaced the burnt bulbs,lubed the tuner slider and pulley, and tried my best to adjust the tuner, and cleaned the chrome, etc. It sounds pretty good, haven't really tested it out too much. I have noticed a few issues, if you can call them that.

Issue 1.) When I turn the volume knob nearly all the way off, almost 1/16th of a turn before it is fully off, I have a slight uneven channel shut off. As I turn the knob to the off position, the left channel drops out before the right channel. Should I be worried? This is only noticeable with headhones. Also, if I plug in headphones with their own volume control and turn the volume off on the receiver, but crank the headphones volume up, I can still hear the radio, but it is very faint. Am I over scrutinizing this?

Issue 2.) When I first turn on the unit and wait for the relay to engage, it sometimes takes six seconds for the relay to click. Is this common for this model? Should I worry?

Issue 3.) When I first switch on the unit, and it warms up, and once the relay is engaged, when I go to adjust the bass and treble, no matter if it was left at + or - the first click from the last position, either the neutral center, or whatever level I had it on, my speakers make a popping sound when I click the knob to a new level. This happens with both the treble and bass, but only when the unit is first powered on. Subsequent dial adjustments do not cause this popping sound. Could this just be the unit warming up? The popping is very subtle, almost like a little click. Not to be confused with the clicking of the indentation on the dial. Hardly noticeable, only with headphones.

Issue 4.) The tuner seems to be .2 off. For example, when I tune in a channel that is on 100.7, the tuner dial will have to be on 100.6 or 100.9, with the case of 100.7 I get the best reception on 100.5. But this is for all FM and AM channels I tune in. I can get most channels. Now, in my area the FM channels seem to be really close together, could it be that it is just having trouble tuning it in? I had an old GE alarm clock with the same issue, analog tuner and it would always be a tad off from what the dial read. I looked at the service manual for this model and it is not only confusing, it looks like I would be liable to break something. Should I fret? I can get all my stations, nice and strong, fully stereo, just it isn't "spot on."

Finally, what are some tips and tricks to watch out for, it seems to sound great and I have inspected the capacitors for leaking, bulging, and corrosion. All look original and all look to be in great condition. I also tested, with the unit off and with the caps discharged, and all of the caps test well within respectable range. I hear horror stories of people going "never power on an old receiver without recapping it first! You'll blow it up! Even if they look good, they might fail." On the other hand, you hear people say "If you replace them, you could get a bad batch and then it will sound worse!" Also, I checked the power packs, they both test fine. I haven't driven it too high, not wanting to pop anything. From what information I have given, should I be ok?

 

[txturbo]

Welcome to AK!

1. Volume drop out. You can try cleaning the volume pot again however what you describe is not uncommon. If your critically listening with headphones expecting the volume to track perfectly to zero it's probably not going to happen.

2. I can't say for sure about the delay time for this model. Generally speaking it takes a couple of seconds on other models for the relay to close. If you experience longer times you may want to investigate the circuit further.

3. Your controls are probably still dirty. Sometimes it takes 2-3 cleaning cycles to really get things clean. How are you cleaning the pots?

4. If I understand your description you have some slack in the tuner string? You state that if you tune to 100.7 your actual center tune is a bit higher or lower. If your receiver consistently tunes higher or lower than indicated then you could potentially adjust it mechanically or electrically.

Have you checked the bias and offset of the amps?

You may want to do a search for Pioneer SX-780 recap threads on Audiokarma. Lot's of great information.

 

[larryderouin]

As a 790 owner (black dial version of the 780) for 9 years now, I think I feel somewhat qualified to answer most all your questions
1.) a.) No. this is normal on older potentiometer based units. They wear, period. B.) Over scrutinizing? Yes.
2.) The Normal span for relay engagement on ALL PIONEERS is between 3-7 seconds. Your oK.
3.) This is charging of capacitors in the tone circuits. Normal. If it gets worse and or on all adjustments, then you need to recap the tone board area. The 780 is a single board unit so you'll need the board layout drawings in addition to the schematics.
4.) In your case the dial pointer is .2mHz low (100.5 VS 100.7) ON fm. You didn't say how far off or on the AM side was so I'll presume it's close as AM is Broadband and close on AM is like Hand Grenades and Horseshoes. Unless you are Obcessive compulsive and it's keeping you up at night worrying about it, I'd leave it alone. It can be fixed but sometimes you make it worse, like breaking the tuning string and then you have to restring the damed thing. Again Unless you are OCD and it's keeping you up at night worrying about it. don't mess with it.

As for things to look for, #1 in everyone's book for the 780 is the voltage Regulators. They generate gobs of heat and that heat goes right down the transistor legs and most times de-solders them. Replace with the designated uprated replacement transistors and install larger heatsinks on them. The back side of these transistors are electrically "HOT" so watch what you touch. Adding mica spacers and nylon scews/nuts to insulate the heatsinks is a good idea. Also I've found that the Larger Diodes sometimes De-Solder themselves. Just re-touch the solder on them.

Speaker wires. Dont' just twist them,.......Twist them and then solder them so no loose strands appear. do this for both sides. the 780 packs hate bare wies touching as it causes an immediate and FATAL casualty to the PACK. ALSO DO NOT HOT-SWAP speaker wires or RCA CABLES ONTHE BACK. It can kill the packs. You've been warned.

 

[Spin_Vinyl]

Thank you for your replies. Yes, the AM is also a little off. I mean, if I am not staring at the dial and just listening for my channels to tune in, it doesn't matter. I would mess with the dial cord (string) but I don't want to risk breaking anything. It looks to me as if someone already added some spacer washers to the back of the voltage regulators. As for the volume tracking, maybe I have my rose colored glasses on when it comes to classic audio tech. I was worried that something was out of wack and I needed to adjust it. I guess I should resign myself to the fact that this is just a nearly perfect electronic device assembled by imperfect people nearly forty years ago? Hmm, my speaker wires seem to be pretty tidy. I might look into getting some of those crimp on right angle plugs to pop into the speaker terminals. I would NEVER think of hot swapping audio cables, what monster does something like that?? Not only will the static mess with something, wouldn't the buzzing and popping potentially blow a speaker?

 

[Spin_Vinyl]

Furthermore, I know this is all opinion, but...I have heard mixed reviews from people on this receiver. Some say it is a good "beginner" vintage receiver, and others say it is utter crap. I don't have $10,000 to spend on audio gear, and my last receiver I had, 90s kenwood, the "audiophiles" I know scoffed at it. Which is partly why I jumped at the chance to grab this one (also because it looks cool). I know there is no perfect solution, but did I do ok with my find? Is it worth it? Or should I keep searching for another one? If so, what are the "good" models of silver?

 

[Imanoldee]

Furthermore, I know this is all opinion, but...I have heard mixed reviews from people on this receiver. Some say it is a good "beginner" vintage receiver, and others say it is utter crap.

Well, THAT is utter crap!
I have restored SX-780's and afterward they sound very nice to me. Plenty of power, and nice clean sound too.

As to the issues you have asked about, others have already given good advise in my opinion.
For issue #1, first try a couple of more de-ox treatments as has been suggested.
If that does not fix it, it could be a worn pot as someone mentioned, or my 2 cents here, it could be a dirty (bad) protection relay.
If the unit is not pulling a lot of juice in the speakers the relay maybe sticky.
I had a different model give me that symptom, and it was a bad relay.

Oh, and getting a working SX-780 for $40 is great.
You can spend another $40 or so in re-capping most of it (without the big filter caps), and you will be set for years of listening pleasure.

If it is a bad relay, a modern replacement is available.
Mouser number #653-my4-02-dc48, which will run about $10 plus shipping, sadly shipping will be $8-9 if that was all you ordered.

 

[larryderouin]

Back in 78-80 the 780/790 was argueably the most popular model (by sales) they made. This is one (of many) of the reasons there are so many 780 threads in the forum. I would venture to make a SWAG that close to 10-12% of all threads in the Pioneer Forum are related to the 780. They ran on STK POWER PACKS and the originals are not being made anymore (all made now are chinese fake repro's) and they are very sensitive to voltage spikes and shorts, which throws off everyone who opens one up looking for discrete components for the final amp. So they come looking here for answers.

YOU DID GOOD! The going price range for a working 780/790 is over 100 to 150 or so last I looked. I've seen them as high as 2 bills. As far as yours is concerned it apparently has a couple of small niggling problems that aren't critical to operation of the unit, but are more from age and wear. The pot problem isn't a matter of poor performance ofthe line workers, it's the result of a metal wiper swinging across a carbon track, which will eventually wear out. This is normal on all units, and depending on who actually made them, sooner rather than later. 60's FISHER, SCOTT, SHERWOOD, ETC units have the same problem. So it's not a Pioneer only problem. Unfortunately the pots aren't made anymore so if it ever craps out you'll have to cobble something together or find a parts unit and strip out the pot and hope it's good.

The 780 was the mid level unit in a lineup of 8 units. Apparently it had the most bang for the buck back in 1978-80. @just under $400. it was literally a steal.

Do the recap, uprate the regulators, add better heatsinks to them, and keep the speaker wires separate, and you can enjoy it for 20-30 years before it'll need another overhaul. Maybe by then someone will come up with a replacement STK that actually works or something else in a kit that has the metal work already done.

 

[Spin_Vinyl]

Hey, sorry for not replying sooner. I've been busy with life in general. Thank you for all the info. The receiver is on the back burner for now, until I can give it the attention it deserves. It is better to go all in instead of doing pieces here and there.

 

[jcox]

I have a 780 and love it! Its a great mid-level unit. Utter crap? Hellz naw! Damn solid, with great performance and looks to match. They are a very common unit, because they are loved and they last. And for $40 a complete steal (assuming the cosmetics are decent). Easily worth $100-150 as is, and 200-250 nice and minty and serviced.

Issues 1 and 3 both could be pots needing another round of cleaning. I have a 680 also with a dirty volume pot, that after a few turns wont crack nearly as much. One of these days i'll clean it.
Issue 2 does not sound normal to me. Mine takes no more than 2 seconds. I'd check the relay as the one member said. Not sure its a problem exactly... maybe could be one soon? Otherwise, kinda annoying for sure.
Issue 4 - I would just move the tuner indicator a hair on the dial cord, to get it where it belongs. This is unavoidable whenever the unit is re-strung, and it probably was. (unwrap the dial cord from the indicator tabs, hold the cord from moving with one hand and slide the indicator just a bit with the other; re-wrap the cord on the lil tabs).

Tips?
I havent recapped mine, and its perfect. With vintage stuff, unless you have endless time/money/skillz, I'm in the group that believes if it aint broke, dont fix it. I wouldnt recap unless theres a problem. Sounds like there's not.
Try wiping the brushed metal face with something like WD40 so it doesnt pick up fingerprints.
I put a strip of alum foil inside under the upper cover, over the dial bulbs, to push more light back down (a bit brighter) and avoid further burning of the underside of the wood cover.

Enjoy! What other equip is connected to it?

 

[jcox]

... Mine takes no more than 2 seconds. I'd check the relay as the one member said. Not sure its a problem exactly... maybe could be one soon? ...

OOPS. Spoke too soon... So I timed my 780 relay last night and it takes FIVE seconds, not 2. I remember it being a bit quicker I thought. Its my "secondary" system so doesnt get used often right now; I wonder if its a bit slower after it doesnt get used? [Someone here will probably laugh at that thought... ha]

 

[Awesomeaudio]

 

[Spin_Vinyl]

Back guys. Sorry for such a wait. If I had waited any longer then it would have been one month since my last reply. Ok, so, to answer jcox's questions.

Current setup is a Pioneer SX-780 hooked up to a Fisher Studio Standard MT-6225a with an Empire 2000 E/III cart connected to a pair of Polk T20e monitors.

The only blemish is it is missing one screw on the side and a slight scuff on the veneer on the back right corner. I tried some DEoxit and it didn't really change the popping on the treble.

I'll take a look into using some foil to help direct the light downward.

 

[Spin_Vinyl]

As for speed of the relay kicking in, I think that is just how it normally is. The same response time whether it has been used all day, or if I have had it sit for a month. So, I think it is the the nature of the beast.

 

[jeffpaletz]

Sounds to me like you should stop tinkering with your nice receiver and enjoy it. I've had the experience of trying to improve something until I broke it. That's no fun.

 

[larryderouin]

Like I said in my 1st post, Pioneer set the relay operating circuit to stabilize after 3 to 7 seconds from power on depending on the unit. The bigger the unit, usually the longer it took to stabilize. The 780/790 takes 5 to 7 seconds ideally. If it's shorter or longer, it's not the relay, it's the R/C network that controls it. Usually it's the capacitor in the R/C circuit that goes bad. So under 3 seconds and you get voltages that are higher than normal for a second or two that could shut it down again until the voltages settle, and longer than 7 seconds is doing no harm other than signalling that the R/C circuit controlling the relay needs work. The relay only does what it's told to do. Off or On.

Spin Vinyl; Your relay time is spot on! Don't worry about it.

 

[Moby Dick]

Congratulations on your nice pioneer.
You picked a great unit for a starting point.

Enjoy listening to it(and looking at it!).

 

[Spin_Vinyl]

Thanks everyone for your replies! If I see another classic receiver I might get it. Not saying I will become a hoarder...err..."avid collector", but I do have a penchant for collecting various electronic gear.

 

[Spin_Vinyl]

Seems to be chugging along just great. Once you crank it up, it sounds great. Really good mids, highs, etc. I don't have a dedicated sub so I don't know how punchy the bass is yet. But so far it seems to be ok. Still has the click when you switch on treble.

 

[gbroot]

Thanks everyone for your replies! If I see another classic receiver I might get it. Not saying I will become a hoarder...err..."avid collector", but I do have a penchant for collecting various electronic gear.

No harm, no foul. You're just joining the rest of us. After I bought my first vintage receiver (uhg, off of the auction site) an SX-750, I decided I better buy a back up unit "just in case". That was the best excuse I could make at the time and probably the most valid. Since then the excuses for adding to the collection defy reason!

 

[larryderouin]

After I bought the 1st console and gave it to the wife, I had to have another, and another, and another, ad nausem. I was up to 14 but a couple got ruined in a flooded basement in 2012 hurricane. So I'm down to 11 now, but my receiver stock is growing at about one a year.