Pioneer from the 70s is it worth fixing?

[bigdaddy]

My brother in law found an old pioneer receiver at a garage sale(sx 1500 td) and gave it to me. I decided to hook it up and see what the fuss is all about on the old stereos. At first I couldn't get any sound(mute button is sticky) and then I got sound but only one channel. This unit has outputs for 3 sets of speakers, so I hooked up both speakers to the right channel of different outputs. I just can't believe the sound quality of this old stereo. It has a switch on it for mode that will play only the left channel or only the right channel or combine both for mono. I believe this is the problem because it does nothing. Also the backlight for the tuner is not working but I'm sure that's an easy fix.

[ClaudeJ1]

Any solid state amplifier that was designed without the low Transient Inter-Modulation principles of Dr. Matti Otala of Finland. This makes most of the units built in the 70's questionable in this regard.

[HarryO]

Worth Fixing?

The first thing to do is check for blown channel fuses inside the receiver.

Next, Clean the switches including mode select, AND tape monitor switches on the Pioneers. You'd be surprised how many tape monitor switches make one channel cut out. (or both)

A dirty volume control can cause one channel not to work also. I've got one here now that I have to "play with" to make the right channel come on. It's one of my test receivers and I'm used to it so I won't waste my good cleaning materials on it.

Most of these old Pioneers will sound many times better with just a good cleaning.

Harry

[Daddy Dee]

I'd suggest to get under the hood to see if there are any fuses on the board. It's possible the fix is as easy as that.

You are right, the lights are a pretty easy fix. Some of those receivers used a lamp that looks just like a fuse. It's a glass tube with metal end caps. Parts express stocks these in a couple of values.

[bigdaddy]

Any solid state amplifier that was designed without the low Transient Inter-Modulation principles of Dr. Matti Otala of Finland. This makes most of the units built in the 70's questionable in this regard.

So is that a yes or a no?

[bigdaddy]

Thanks for the replies guys. What is used for cleaning the switches? I'm betting dish soap might be bad. I've always bought electronics and thrown them away when they stopped working. So cleaning switches is new to me.

[Daddy Dee]

Radio Shack has got an electronics spray cleaner that leaves no residue. Caig's Deoxit is a favorite.

Just spray some down the shaft into the pots and have a twisting party. Rotating the pot many many times is needed.

[ClaudeJ1]

Any solid state amplifier that was designed without the low Transient Inter-Modulation principles of Dr. Matti Otala of Finland. This makes most of the units built in the 70's questionable in this regard.

So is that a yes or a no?

No, unless it's for background music in a garage.

[thebes]

I guess this is what Claude's talking about, but let your own ers be the quide. Most of those Pioneers were strictly mid-fi, but compared to a pocket transistor radio, were a revelation:

" Moving
on to electronics, the power amps of the late Sixties and early Seventies
blew up a lot and sounded pretty nasty. The engineers of the early 1970’s
were still wrestling with problems like maintaining adequate phase margin
with real loudspeaker loads, Nyquist feedback stability criteria, Safe
Operating Area for the driver and output stage, and little things like that.
Audionics’ first amp, the PZ-3, fit right into this picture: loads of
feedback, and very low THD distortion measurements. (0.03%, get it?) It
measured just fine, but it wasn’t too stable in the real world, with an
alarming fondness for shorting out driver transistors, smoking bias
resistors, and shooting flames out of the cooling vents (in anticipation of
the much larger solid-state melt-down at Three Mile Island).

I
remember many days when more of these dogs came back for repair than we
shipped out. Some of the amps had circuit boards scorched beyond
recognition, and top plates discolored by lines of dark-gray soot. We’d
replace the circuit board, repaint the top cover, and ship ‘em right back
out again. Needless to say, the PZ-3 was not a big money-maker for
Audionics. The only consolation was knowing that all the rest of the
high-powered transistor amps were just as bad.

In
the mid-Seventies, along came Matti Otala and the discovery of TIM (slewing)
distortion. Our Number One engineer (the conservative old-timer who designed
the PZ-3) was utterly horrified by Otala's first AES paper and said it was
unscientific bunk or worse. Our young Number Two engineer took Matti
seriously, let “traditional values” go by the board, and tried different
approach.

Bob
Sickler let the distortion rise up to the 0.1% level, by making very large
decreases in feedback (feedback dropped from 40-50 dB to 20 dB) and using
the most linear complementary-symmetry topology possible. The slew rate and
power bandwidth improved by a factor of 10 to 50 times. Best of all, we
couldn’t toast it, even with my speaker simulator load hooked up.

In
1976, Audionics introduced the CC-2, which was probably one of the first
low-TIM amps in the US. Sure enough, it sounded much better than the PZ-3,
and the failure rate in the field was well under 1%. The reason for both was
probably the >200kHz power bandwidth and an excess phase margin of 60
degrees, both quite unusual at the time. Although I rarely listen to my CC-2
these days, it’s still not a bad transistor amp; by now, though, nearly
all transistor amps use the same design principles as the CC-2. Matti’s
paper had such a profound impact on the solid-state design community that
nearly all high-end engineers got on board ... besides, it’s hard to argue
with better reliability, which a high slew rate and adequate phase margin
certainly provide."

[oldenough]

Wow!!! whoddathunkit???

[oldenough]

Yeah all the BS and long winded rhetoric aside, they can actually sound pretty good. Let your ears be the judge.[]

[bigdaddy]

Yeah if I can fix it as easily as a clean up and maybe a fuse or two I'll do it. It'll do for music in the upstairs anyway. But I do like the sound of it anyways.

[bigdaddy]

I guess this is what Claude's talking about, but let your own ers be the quide. Most of those Pioneers were strictly mid-fi, but compared to a pocket transistor radio, were a revelation:

" Moving
on to electronics, the power amps of the late Sixties and early Seventies
blew up a lot and sounded pretty nasty. The engineers of the early 1970’s
were still wrestling with problems like maintaining adequate phase margin
with real loudspeaker loads, Nyquist feedback stability criteria, Safe
Operating Area for the driver and output stage, and little things like that.
Audionics’ first amp, the PZ-3, fit right into this picture: loads of
feedback, and very low THD distortion measurements. (0.03%, get it?) It
measured just fine, but it wasn’t too stable in the real world, with an
alarming fondness for shorting out driver transistors, smoking bias
resistors, and shooting flames out of the cooling vents (in anticipation of
the much larger solid-state melt-down at Three Mile Island).

I
remember many days when more of these dogs came back for repair than we
shipped out. Some of the amps had circuit boards scorched beyond
recognition, and top plates discolored by lines of dark-gray soot. We’d
replace the circuit board, repaint the top cover, and ship ‘em right back
out again. Needless to say, the PZ-3 was not a big money-maker for
Audionics. The only consolation was knowing that all the rest of the
high-powered transistor amps were just as bad.

In
the mid-Seventies, along came Matti Otala and the discovery of TIM (slewing)
distortion. Our Number One engineer (the conservative old-timer who designed
the PZ-3) was utterly horrified by Otala's first AES paper and said it was
unscientific bunk or worse. Our young Number Two engineer took Matti
seriously, let “traditional values” go by the board, and tried different
approach.

Bob
Sickler let the distortion rise up to the 0.1% level, by making very large
decreases in feedback (feedback dropped from 40-50 dB to 20 dB) and using
the most linear complementary-symmetry topology possible. The slew rate and
power bandwidth improved by a factor of 10 to 50 times. Best of all, we
couldn’t toast it, even with my speaker simulator load hooked up.

In
1976, Audionics introduced the CC-2, which was probably one of the first
low-TIM amps in the US. Sure enough, it sounded much better than the PZ-3,
and the failure rate in the field was well under 1%. The reason for both was
probably the >200kHz power bandwidth and an excess phase margin of 60
degrees, both quite unusual at the time. Although I rarely listen to my CC-2
these days, it’s still not a bad transistor amp; by now, though, nearly
all transistor amps use the same design principles as the CC-2. Matti’s
paper had such a profound impact on the solid-state design community that
nearly all high-end engineers got on board ... besides, it’s hard to argue
with better reliability, which a high slew rate and adequate phase margin
certainly provide."

Thebes your going to make me go get out a dictionary aren't you? LOL

[HarryO]

Radio Shack has got an electronics spray cleaner that leaves no residue. Caig's Deoxit is a favorite.

Just spray some down the shaft into the pots and have a twisting party. Rotating the pot many many times is needed.

Actually all the old Pioneer have open pots and should be cleaned from the inside along with the shafts from the outside. The openings on the pots will look like "crimped" places. Put a shot of cleaner in both sides of the crimps and rotate the shafts a couple of dozen times or so. Do the same on the switches and buttons.

Turn the reciever on it's back, rotate the shafts, and then turn the receiver on it's face and rotate the pots a couple of dozen times again.

DO NOT spray the tuner fins with DeOxit. It leaves a residue and is harmful to tuners. Non-residue sprays only on the fins.

I find it easier to use a non residue cleaner on the pots and shafts initially and then a very light shot of the DeOxit last.

The backs of the switches and buttons are also open and should be given a light shot of DeOxit after cleaning.

The Pioneer uses an 8 Volt fuselamp for the face backlights.

BE SURE TO LET THE CLEANERS DRY BEFORE POWERING UP!!!!!

If you have an air compressor it wouldn't hurt to blow the dust out of the receiver and excess cleaners from the pots and switches.

Harry

[stormin]

Basically pre 1972 and mid to late 80's SS was near garbage. But the vintage 70's gear that is popular on most audio sites and fetching the higher prices on ebay was built very very well and sounds fantastic on horns.

Again, let your ears be the judge.

[bigdaddy]

I did find two 3 amp fuses and one of them was blown. I'll replace them both I also found the lamps very easy to replace. I'll see if cleaning the knobs and push buttons and replacing the fuses make the left channel work. It's a fun project anyway. Thanks for the help guys.