Realistic SA-100B mini stereo amplifier repair and test

Mini stereo amp from the early 70s was sold at Radio Shack as an entry level component. Although this one works, it has issues and is in need of repair.
One error I found after editing: I called one resistor orange orange black, should have said orange orange brown (330 ohm).

[@danielrine3103]

Hi John, great video, I remember this amplifier. I was around 15 or 16 when my parents bought me this amplifier for Christmas, I also bought the matching AM /FM tuner to match the amplifier they had the same form factor. Thank you for sharing this, brings back a lot of great memories for me......

[@johnpick8336]

My first Stereo Amp...awesome in 1969 !!!

[@aurthorthing7403]

I dig these old amps. I wish I appreciated them more when I was a kid.

[@Rainbow__cookie]

Yeah

[@MusicalBox]

Always interesting stuff no matter what the subject of you video is. And I always find something new to add to my pile of knowledge. You deserve way more views and subscribers.

[@iblesbosuok]

Wow! Vintage old stuff, even older than me. Cheers from Indonesia

[@glenk0]

This brings back memories. This was my first stereo, a hand me down from my older brother.

[@snaprollinpitts]

EXCELLENT VIDEO!!! now I know how you go about troubleshooting an amp, and diagnosing a problem. thank you very much!

[@raymondheath7668]

Wow, positive ground. Takes me back to 50's style car radios

[@johnpick8336]

I brought one new in 1970 with a big pair of Realistic Speakers. For the time, it sounded pretty good .

[@g1fsh]

Nice job John well worked out. Its still good to save the basic stuff that some would just throw out.

[@1danny2k]

I recently repaired a similar era amp. Cut off the power amp section. Left only the preamp and tone control. Added a new transformer long with a tpa3116 chip amp and she sounds nice.

[@ronshaw80]

I had a version of this, about 1970 or so. If I remember correctly, it was a gold front panel. It was sold as a kit or assembled. I also had a matching tuner. For what it was, it actually sounded OK.

[@theolmaestro]

Great video, John! I had a similar model to this in my early days.

I thought this was a great video.Most of us don't have the time or patience to deal with stuff like this- it's obvious you do this because you love it. Thank you for posting the event.

[@snaprollinpitts]

hi John, great video, even the second time around. could you please make a video on how you setup the scope to show the spectrum analysis. show all the formulas you use for all your power measurements, and how you get them. that would be super helpful, so some us out here can do some of the stuff that you do. thanks mike

[@VideoRanger]

I have this amp and the matching tuner. Enjoyed the video.

[@sobakete]

Very nice diagnose work. Cheers

[@crisvel5080]

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[@LePhone620]

I love this video, good job!

[@pyroslavx7922]

I found similar/same one discarded, and i'm from Europe, Slovenia, and i remember "having no bass" on both channels, but at times i just stuck it in tonne or two big pile of crap stuff i "mentally marked as repairable but not resellable at profit" ;-) Might dig it out now again and check component values... Nice brave cat you have ;-), mine is afraid of wires and ropes since she chewed through and shorted tv power cable (got just minor burns in mouth...thankfully), and a dog that thinks everything that gets worm or blows out warm air/exhaust is alive and wanna play "catch me" with desktop PCs and gasoline generator i just finished repairing ;-)

[@JohnAudioTech]

My cat is a wire chewer too. He chewed speaker wires and patch cables. Thankfully, now he leaves them alone.

[@boonedockjourneyman7979]

Try figuring this one out on your simulators Evan’s Hall boys! Nice work John.

[@twotone3070]

Great video, just the sort of thing I enjoy. Subbed. Very minor point, the resistor I could see was orange, orange , brown - 330 ohm, not black?

[@robertneill3057]

Replaced a noisey potentiometer on a Metrosound amplifier. The amplifier had discrete transistors, a single polarity supply by a dual diode rectifier (centre tapped transformer), and the dreaded output coupling capacitors (speakers pop on switching on the amplifier). Noted a capacitor had been replaced when replacing the potentiometer. Had trouble connecting a later seperates tape deck to this amplifier (would howl when recording). Needed the record out lines to be further attenuated. Finding the components to do this externally was hard(modular phono jack assembly). Needed a 3D printer to make these components.

[@douglashoff95]

That typical dual secondary driver transformer of the era when germanium pnp transistors were used as outputs.

[@barneymiller844]

Good video john

[@andymouse]

I hope it live's long and prosper's...cheers.

[@AaronBilger]

I have an old kenwood basic M2 amplifier and the bass is very weak it has no preamp it is plain as be does it need new capacitors? it is from 1983 or 1984 it was only made those two years

[@isaacbell2426]

Cool Hammond grooves!!

[@joohop]

Well Done My Brudda !

[@listerine-pr5lt]

I Have seen similar amplifier diagram in radio from that amplifier time of manufacturing and all were around one watt.

[@Macleodking]

I picked up an old Optimus SA-155 amplifier. I plugged in headphones in the front 1/8" jack and got a prominent hum, which doesn't change if I manipulate switches or the volume. I plugged in a signal in the front Tape/CD 1/8" jack. Nothing. When I ran the signal with a 1/8" stereo to RCA stereo jacks into the tape/CD jacks in the back, I get sound, which I can control with tone, balance, and volume, but I still have a slightly lower constant hum. What should I be looking for here?

[@Rainbow__cookie]

I love your cat Goes away from the window then back again 2 times 🤣

[@andreweh4]

I was a service tech back then and I can tell you that it is total folly to try to repair that amp without thoroughly cleaning all switches and controls first. You will probably just end up chasing your tail.

[@larryshaver3568]

I have a realistic "Rhapsodie" receiver with a noisy channel in the pre-amp section, I have no ideas how to get the board out, Any advice?

[@danielsmith9978]

Hello, Thanks for the video. I have one of these amps and the right channel is almost inaudible. Could you post the schematics of this amplifier? Really appreciate it if you could do that!

[@tatialo37]

I miss the shack!!!

[@t1d100]

Interesting = very enjoyable = thank you.

[@HillsWorkbench]

Now rake out the guts and install a chip amp! I'd recommend (late)that you clean that and the RtR I gave you before handling, could be mouse dirt, could carry disease.

[@bjorn2fly]

Its rated 10w per channel peak, so they knew how to lie back in the days also.

[@6p1p]

2SB415 maximum only 1A , i wonder how it archive 10W per channel..

[@RONWOLPA]

All Toshiba Germanium PNP Transistor , typical 2nd half of 1960s design , 2SB440, 2SB415 transistors. Crossing the ocean on that time , Philips , Telefunken and other european companies were employing similar design with germanium pnp transistors like AC 116 , AC 128 K , etc.

[@terencekaye9948]

HI John,, Great video,, where did you find the Schematic for this amplifier?

[@JohnAudioTech]

I searched the model number under Google images.

[@jeffclark5206]

What song were you using at 16:14?

[@385MrBill]

John, I have the same amplifier and the left channel was very weak, I recapped the unit and now the left channel is much stronger but now there is a low static heard in the left channel even with the volume all the way down. I do not have the skill level or meters that you have but can you steer me in the right direction.

[@JohnAudioTech]

Excessive noise can be caused by a noisy germanium transistor. They are known for going bad that way.

[@steveone]

Thirty nine minutes . A new record !

[@JohnAudioTech]

It was pushing an hour before I edited it down. It took forever to upload with my slow internet.

[@friedmule5403]

Really great video!! I do know about nothing about electronic, so sorry me for asking, but why not just change all the caps and then diagnose afterward, then you know that all the caps are working? :-)

[@kennynvake4hve584]

You were close, it cost $29.95 in 1969

[@iceberg789]

interesting looking old amp, were those harmonics due to germanium transistors or due to design issues ?

[@JohnAudioTech]

I'd say it is a design issue. Tubes and transistors are non linear devices but can be used in a very linear high performance amplifier with proper design.

[@iceberg789]

i see, thanks !

[@Margarinetaylorgrease]

Perfect late night amp. No bass but, loads of distortion in the bass.

[@dbingamon]

I have one of them. Replaced the transformer in it once.

[@MuhammadAsif-si6fb]

You have a good speakers pair. I m from Karachi Pakistan

[@ufohunter3688]

Yes. I see the schematic and some parts looks like a puzzle to me. It would be nice if some one who is knowledgeable about each part of the circuit, to go through it and explain every little bit as to why it's used. I for one, would watch a video like that no matter how long it is.

[@SERVISLAPTOPJOGJAPRO]

You also mention orange purple.... For 4k7. Should be Yellow purple...

[@nigelpearson6664]

It's hard to see how this came to market when quite complex in design meaning some thought went into it. Rogers in the UK made a similar design with excellent power and low distortion about the same time. It could have been much better and been cheaper to make. $35 then was not cheap.

[@gabrielhamburger8823]

The funniest part it is on the 7.minutes 9 second !! And sound stereo!!

[@dhpbear2]

8:40: Those metal can transistors are Germanium. They basically suck for anything Hi-Fi. Although, makers of guitar effects pedals RAVE about them! Beware the (possible) positive-ground power supply in this amp! Most Germaniums, are PNP (haven't watched the rest of the video yet)

[@JohnAudioTech]

Yes this is a PNP germanium amp with positive ground.

[@larryshaver3568]

that's what i thought ,the styling looked more like 70's styling

[@jp040759]

Date code on 1000uf cap is 1970 5th week. Must be 1971.

[@danielsmith9978]

Found the schematic on-line: myphotos.mypclinuxos.com/images/lfever/sa100bschematic.jpg

[@afzaalkhan.m]

Good but Too verbose