I remember those Hitachi FETs very well. For a while almost every HiFi amplifier used them. I made one myself which I used for a number of years. It took a while to get used to seeing small signal transistors without heat sinks driving a pair of FETs giving 100 watts or so. As fast as they came in, they were gone! No idea why they went out of favour. I loved them. Almost never failed and did sound good and very easy to drive and bias. In the UK most Realistic stuff was low end, even the name was a bit of a joke, but nice to see they could make a good piece of kit. PS. Looks like Jim Hough is bored...plus I have no idea what he's talking about, cannot be about amplifiers.
Wow, I had one of these - it was one of the sweetest, smoothest sounding pieces I've ever encountered. To my ears it had the smoothness always promised by valves combined with the muscle of solid state components. My unit looked like it had been knocked to hell and back, but the amp portion worked beautifully; I wasn't concerned with the barely functioning tuner section as radio here in Bermuda is a complete waste of time. I'd give anything for one of these again.
One technique that I have seen other restoration guys use on these amps is to replace the trimmer pots used for adjusting finals bias with a multi-turn pot. They aren't physically much bigger and you can dial the bias in exactly with ease. Another great vid xraytonyb! I was a Realistic STA-2100D owner back in the early 1980s. I sure miss that receiver. Cheers!
tony, not sure if you will see this but just wanted to let you know, it is the capacitor used in the zobel that fails. i recently picked up a quadraflex 650r fet. (the amp is virtually identical to the 2200 and they were both made by tandy) anyways, it was oscillating. i tracked it down to that chicklet looking cap in the zobel. i made a thread about it on AK. the next week, someone had a concept 11.0(also made by tandy) that was oscillating, same brand of cap had failed. the name is "qualicomp" . they have an "omega-esgue" looking logo on them. just a heads up for anyone, they should be replaced on sight.
As a kid I looked down on Realistic anything. Their amps & receivers were priced right for a teenager with a part time job. So I bought some amps and Mach 1 speakers. Years later I learned that some high end companies did the manufacturing for Tandy, Realistic. I know now that though they were the #1 mass marketer quality could be truly high end. A few years ago I bought a mint STA-2600 which honestly sounds better than some name brands today. Would love to find one of the STA-2200 mint. Tony you sound like a down to earth guy with a wealth of knowledge. I greatly enjoy your presentation and observations. Mary's husband Peter
Always enjoy your postings don't change a thing. I'm just about to put the finishing touches on an STA-2250 also digital tuning. The power amp is put together like your 2200. However it uses Bipolar Transistors and both channels are on a single board and all four outputs share a single heat sink. Both outputs on the left channel were shorted. After extensive checking the amp board I could find no other problem and fired it up. The DC on the speaker leads is 10mv well within the 50mv allowed. According to my ESR meter all of the capacitors are good, It's working so well I'm tempted to clean the controls and button it up. I've had it playing in my shop for two days now and the heat sink is just warm. What's not to like, I'm keeping this one for myself.
Howard, not to be a jerk but one thing is the dc offset and other completely different thing is the idling current of the amp. Offset should be as close as possible to 0 meaning if you have 10mv in your speakers outputs, most likely your main caps are about to fail or you need to recalibrate those pots. Whereas the 50mv he measured at those big resistors are the idling current of the amp and it has to be as close as possible to 50mv or you'll start hearing a lot of intermodulation distortion.
@@CofeeAuLait I was following the instructions in the Realistic STA-2250B service manual, Which are and I quote;...1. Check balance by measuring across the L and R speaker terminals. DC voltage should be + - 50mv. 2. Idling current adjustment, Adjust voltage across emitter resistors R541 (L channel) and R542 (R channel) to 10mv + - 2mv with 8 ohm load using VR501 (L) and VR502 (R). I see I left out what the idling current was but it's in specs on both channels. The term offset was not something we used back when these were new, voltages on the speaker terminals was simply referred to as DC voltage or DC balance.
Thank you! I learned a few new things about mosfet transistors. Good explanations about working on stuff and how it works. And what i like about you're way of working, is that you pre-replace diodes, capacitors etc in amplifiers. I have seen many man just replacing faulty ones, or non at all, while the amp is more then 30 years old. I work the same way. edit: I would have replaced those bias trim pots as well. These are not the most bad ones, but just to be save. Old tranistors are hard to get by these days.
Of i had a high-level piece of equipment like that i would trust you with because I trust your judgement! That's why I love your channel because you do exemplary, thorough work. When you repair a piece of gear you want to make it last another 10 or 20 years! Kudos!
I appreciate your methodical approach too many bulls in the China shop myself included. I watch you to learn and practice patients and improve my trouble shooting abilities thanks for all you do!
Thanks for another video Tony, I really enjoy and learn from them. I was in The Hospital Of Special Surgery on East 70th this past Thursday for my Daughters MRI. I said aloud to myself, gee I wonder if Tony worked on these machines, and my daughter asked who's that? I started explaining and she laughed. I am looking to get myself in some sort of school for electronics to do better troubleshooting and understanding my scope and other equipment. Your stories are just fine, my youngest Daughter herself was born in a pool in my living room in Washington Heights
I have a realistic MPA-100. It is very rare and is 100 watts a side. Not an integrated amp only 1 input but has built in EQ/digital VU meters on front face. It is a truly amazing amp.
No! No just meat and potatoes. Follow-up and background story is also very important. I like your videos. Very much. Not just from the learning point of view. Keep them coming. Thank you very much for this amazing content you're putting out.
xraytonyb: O, my God! I am reading a magazine with receivers, the most modern amplifiers and other audio. But this receiver is much more beautiful than most of the modern equipment!
I had the STA-2250 and it would rock...and sound so good...I believe it was made after your receiver ....and I got it new in 1980, along with RS T110 tower speakers which sounded ok....
All of the receivers you mention in the video were manufactured by Tandy Electronics. They were an excellent manufacturer, and were contracted to produce the Quadraflex and Concept line of receivers for Pacific Audio. The dual mono Concept 16.5 may be the best ever.
I remember when Hitachi first released those Mosfets and the circuit they initially designed to run them. Many companies used this design without much modification. It was ok, but was soon improved upon, including by Hitachi themselves on their MK2 version of their HMA7500 power amp. You should really use anti static precautions when handling them. Thanks for another instructive video.
definitely don't listen to the people in the comments your videos wouldn't be the same if there wasn't any commentary. I don't think i would have been able to learn as much as i have if you did your content "wham bam thank you ma'am " style
He teaching my dumb as s skills, Arthur. I try to collect as many as I can over the years. I learn a few things every day but I've never seemed to learn it all yet.
Another fine video. Thanks so much for sharing the audio equipment videos. God bless you and your family and keep you safe. Good holiday season to you and yours too.
I picked up this fantastic receiver two years ago and love the sound it puts out. Outstanding work ! If you’re interested in some work? Love to get it refurbished
Very wise on the no power up those caps could be hiding some nasty surprises Happy holidays! And keep talking I listen more than I watch and it IS your video do it YOUR WAY!
Been looking for some tweakability in the schematics. Here's what I found: 1. Yep, it wouldn't be an early PLL synthesizer if it didn't have a 100k resistor on the VCO tuning diode (R13). That's 40 nV/sqrt(Hz) of finest thermal noise right there that'll be modulating your VCO, increasing phase noise and hence audio noise floor. Try, I dunno, 3.3k + 3.3..10 µH instead. 2. I would also whack an electrolytic on the 78L05 output on the prescaler board, probably on the backside as it's so cramped... pretty much as much as you can make fit. There's only a 10n there so staggering two different values (like 10µ + 220µ) may be required to avoid problems with parasitic inductance. 3. Like most anything from the time, this unit is lacking FM RF or IF AGC, and the IF strip is a typical Japanese limiter-amplifier job of excessive gain and poor linearity _(screw those textbooks! we want better quieting!)._ However, RF amp MOSFET G2 is easily accessible via terminal 4 on the frontend board, so one could build something there with some extra circuitry. Maybe like this - www.ham-radio.com/k6sti/rfagc.htm - but possibly with some extra pull-up as the MOSFET doesn't seem to be run quite that hot here, looks like ~4 V on G2. A *lot* of effort has gone into cleaning up the supply rails in this one, with low-noise regulators followed by RC filtering. (This reminds me of another house brand receiver I've seen recently, a (JC Penney) MCS 3248.) Unfortunately, output noise floor is still going to be only so-so, with an SNR of around 95-96 dB - intrinsic noise floor of the preamp isn't particularly low, and total gain at ~45.7 dB is around 2 dB more than it really needs. Not bad for the day and OK on normal sensitivity speakers, but I definitely wouldn't run Klipschorns without a 12-20 dB attenuator between Pre-Out and Main In! 4. Noise could be reduced a good bit in Tone Defeat mode, at the cost of somewhat increased loading on the preamp output (and hence a bit more distortion). Replace R621 (56k) by 22k, and either R623 or R625 by 4.7k. This should bring SNR up to 99 dB. About 3.5 dB less noise (including 1.5 dB as a result of reduced gain) is pretty decent. If you're really fussy about this stuff, you can always connect a good preamp externally between Tape Out and Main In. Power amp noise levels should be very low.
The STA-2200 was Radio Shack's first and only MOSFET receiver. But it was the second model they manufactured. The Pacific Stereo Quadraflex Reference 650FET R was manufactured by Tandy Electronics a couple of years earlier, and was the first receiver to use the Hitachi MOSFET outputs. Rumor has it the STA-2200 was heavily influenced by the 650FET R. Would love to see a comparison of the two.
i wouldn't call it influenced, i would call it an updated version. my 650fet has a few things going for it over the sta2200. black face. analog tuner. dc offset adjustment.
This is way late, like 5 years late. B.ut the issue about TO-3 packages is that the case is the Collector on bipolar transistors, and it is called Drain on Mosfets. That is, whether N-channel or P-channel. Another conclusion I have is that the idea for the 9-V battery was expected to support the clock and station memory just over any short time power failures. Maybe the designers imagined it was related to the small transformer. But yes, it is nuisance, probably part of the main power. No matter, you are right - the battery is out of its “juice” in too short order. Another note, I recall seeing on my unit a note to the effect that the STA 2200 was made by Hitachi.
Radio shack got a bum rap back in the day for their audio gear. It has stood the test of time. This one is definitely worth putting some time in to restore.
Hey there bud, I figure its high time I vocalize much I enjoy your videos...Feel like I'm gaining tech wisdom through osmosis. The story you told us about how your dad essentially paid for his own birth hit me right in the feels, that you'd share such a personal anecdote with us idiots. Keep up the great work and thank you for your dedication!
As far as my experience and data sheets of American MOS-FETs in TO-3 package indicate, the case is always the Drain. I am not sure about possible difference in Japanese parts. I thought I would just open my STA 2200 service manual and check. But now I cannot find it anywhere... Anyway, my unit has two problems. The various pushbutton switches are in need of cleaning and probably (but not finally verified), for same switch issues - on power up it often starts chattering the safety relay. One of these days I’ll take it open again. My previous attempts have led to a loop containing the safety relay circuit, the phase lock circuit and a bunch of those switches.
Its an amplifier that want's to be an amateur radio transmitter when it grows up ! its just practicing a little out of band for the 80 and 40 meter bands :-) :-) Have a Merry Christmas and a Happy New Year !! John Bellas KC2UVN
I was taught that a cap directly across a switch was a no-no. Closing a switch on a charged cap will do not the contacts any favors. You'd need a series resistance high enough to limit the surge current to what the switch can handle. The first set of contacts are already burned. I'm guessing the cap is there to protect the switch when it interrupts the current to the transformer. I'd look for another way to address that problem.
Just keep talking Tony. One rule of broadcasting is to never have more than 10 seconds of dead air. People learn and take in information by narration and not just watching. If people don't want to hear, then they have a volume control.
That unit seems to have plugin modules, I love watching these videos and I hope that you have a Happy and Prosperous New Year, would it be possible to 4.43MHZ Notch filters in before the power stage to try and notch out the oscillations that might happen on either channel.
this is great! so that glue is from the capacitor... and that will happen if you use the amp too much of if you dont use it, or only because it is old? Cheers!
I own one an use speaker wire to try an get fm channels but stuck on same station digital read out moves but a lot of static , should I clean its buttons. I’m lost all else work an loud as hello
My display is really tired. People would plug these in for years on end and with that clock built in.. I keep searching ebay for a AM FM clock radio with a compatible VFD that could replace it. No luck so far.
If you like MOSFET amps, have you any experience with Pass amplifiers? Maybe try and get one for repair, I've heard great things about them. I've seen a kit of a Pass Aleph 3 ripoff on Ebay so could be a fun video to make one. Very cheap (about £30 for a stereo pair) although the expense will be the transformer and heatsinks. May get one to try even though it may be complete Chinesium...
Just cur. How many hours spent in the sta 2200 for the full recapping? I just bought one these , working, on EBay. Trying to estimate the shop cost for this unit. I'm no electronic tech. Great Video, Thanks
Tony. Noted the wire wrap. Did wire wraps provide as good as a connection as a good old regular mechanical ones with solder? Also, is wire wrap used any more? Thanks, and keep them coming. Len
They were a more secure method more commonly used than plugs in that era of electronics construction. It likely had something to do with costs of wave soldering or extra processes commonly involved when having to use plugs and other stuff.
Never touch the gate of a MOSFET with your finger; the human body can easily accumulate 400-800 volts of static charge without even feeling it - that’ll blow the daylights out of the gate dielectric! And if it gets to the point where you do feel the static electricity, or you see the little spark, you’re talking several kilovolts at least! The dielectric strength of (dry) air is about 10 kV/cm, so 1 kilovolt can jump a 1 mm gap. Instead, hook an insulated clip to the gate, then clip the + (red) lead from the meter to the drain, and the - (Black) lead to the source. Now touch the other end of the clip lead from the gate to either the source or drain; source=off for enhancement-mode, and drain=on for enhancement-mode! Finally, you can wire a 1k pot between the source and drain, and connect the center (wiper) of the pot to the gate; you can now observe the MOSFET in action as you adjust the pot. HTH! Also, (note to viewers) never test a line-powered device with line-powered test equipment (such as a scope, frequency counter, spectrum analyzer, etc...) without an isolation transformer, or without verifying that the power transformer in the DUT (device under test) is not shorted primary-to-case, or primary-to-secondary! Failure to observe this can result in your test equipment becoming an expensive paperweight, or the DUT can even be damaged or destroyed!
If you're holding the body of the MOSFET, which is the source, its fine to also handle the gate. But you should never touch only the gate electrode, that's asking for it. Nylon carpets and clothing have no place in an electronics lab in my opinion, so much static with that stuff.
I have the same receiver, somewhere. LOL It is a great unit, but ugly. Yes digital tuning just came out. The battery backs up the computer to hold the presets.
Also (for enhancement-mode MOSFETs), you can tell if it’s N-channel or P-channel by measuring from source-to-drain. If you hook source to - (black) and drain to + (red) and you get high resistance you have N-channel. If you get a low resistance, you’re reading the body diode of a P-channel device. Likewise, if you hook source to + (red) and drain to - (black) and you get high resistance, you have P-channel, and if you read low resistance, you’re seeing the body diode of an N-channel device! This should work for all enhancement-mode MOSFETs, but may not work for JFETs.
Still just a piece of Japanese stuff; nothing compared to my Realistic STA-250 (built in America by Sylvania, circa 1973) , I drove it very hard over the years (and in college) and nothing ever blew up on it; maybe just having to replace some pilot lamps.
Every time I get of my car during very dry, cold weather, I drag my butt across the seat and get zapped! No kidding guys and gals it hurts. That's several thousand volts. I've been an industrial electronics 're h for 30 years and have been shocked many times by 120, 277, 480, and 600 volts ac. These were partial encounters through high resistance barriers (my brain). Those dc static shocks HURT like hell!
Get a Shaxon anti-static wristband. Wearing it without the ground tether will keep you from getting zapped. I wear mine every winter and it works for me. And don't listen to the naysayers, just try it.
I remember those Hitachi FETs very well. For a while almost every HiFi amplifier used them. I made one myself which I used for a number of years. It took a while to get used to seeing small signal transistors without heat sinks driving a pair of FETs giving 100 watts or so. As fast as they came in, they were gone! No idea why they went out of favour. I loved them. Almost never failed and did sound good and very easy to drive and bias.
In the UK most Realistic stuff was low end, even the name was a bit of a joke, but nice to see they could make a good piece of kit.
PS. Looks like Jim Hough is bored...plus I have no idea what he's talking about, cannot be about amplifiers.
Wow, I had one of these - it was one of the sweetest, smoothest sounding pieces I've ever encountered. To my ears it had the smoothness always promised by valves combined with the muscle of solid state components. My unit looked like it had been knocked to hell and back, but the amp portion worked beautifully; I wasn't concerned with the barely functioning tuner section as radio here in Bermuda is a complete waste of time. I'd give anything for one of these again.
One technique that I have seen other restoration guys use on these amps is to replace the trimmer pots used for adjusting finals bias with a multi-turn pot. They aren't physically much bigger and you can dial the bias in exactly with ease. Another great vid xraytonyb! I was a Realistic STA-2100D owner back in the early 1980s. I sure miss that receiver.
Cheers!
Realistic gear always impressed me back in the late 70's and early 80's. It's still impressive today.
tony, not sure if you will see this but just wanted to let you know, it is the capacitor used in the zobel that fails. i recently picked up a quadraflex 650r fet. (the amp is virtually identical to the 2200 and they were both made by tandy) anyways, it was oscillating. i tracked it down to that chicklet looking cap in the zobel. i made a thread about it on AK. the next week, someone had a concept 11.0(also made by tandy) that was oscillating, same brand of cap had failed. the name is "qualicomp" . they have an "omega-esgue" looking logo on them. just a heads up for anyone, they should be replaced on sight.
Oh my, such an Excellent, View, Diagnostic of this receiver..
As a kid I looked down on Realistic anything. Their amps & receivers were priced right for a teenager with a part time job. So I bought some amps and Mach 1 speakers. Years later I learned that some high end companies did the manufacturing for Tandy, Realistic. I know now that though they were the #1 mass marketer quality could be truly high end. A few years ago I bought a mint STA-2600 which honestly sounds better than some name brands today. Would love to find one of the STA-2200 mint. Tony you sound like a down to earth guy with a wealth of knowledge. I greatly enjoy your presentation and observations. Mary's husband Peter
My ears always told me they were high quality. Trust your ears.
Always enjoy your postings don't change a thing. I'm just about to put the finishing touches on an STA-2250 also digital tuning. The power amp is put together like your 2200. However it uses Bipolar Transistors and both channels are on a single board and all four outputs share a single heat sink. Both outputs on the left channel were shorted. After extensive checking the amp board I could find no other problem and fired it up. The DC on the speaker leads is 10mv well within the 50mv allowed. According to my ESR meter all of the capacitors are good, It's working so well I'm tempted to clean the controls and button it up. I've had it playing in my shop for two days now and the heat sink is just warm. What's not to like, I'm keeping this one for myself.
Howard, not to be a jerk but one thing is the dc offset and other completely different thing is the idling current of the amp. Offset should be as close as possible to 0 meaning if you have 10mv in your speakers outputs, most likely your main caps are about to fail or you need to recalibrate those pots. Whereas the 50mv he measured at those big resistors are the idling current of the amp and it has to be as close as possible to 50mv or you'll start hearing a lot of intermodulation distortion.
@@CofeeAuLait I was following the instructions in the Realistic STA-2250B service manual, Which are and I quote;...1. Check balance by measuring across the L and R speaker terminals. DC voltage should be + - 50mv. 2. Idling current adjustment, Adjust voltage across emitter resistors R541 (L channel) and R542 (R channel) to 10mv + - 2mv with 8 ohm load using VR501 (L) and VR502 (R). I see I left out what the idling current was but it's in specs on both channels. The term offset was not something we used back when these were new, voltages on the speaker terminals was simply referred to as DC voltage or DC balance.
Thank you!
I learned a few new things about mosfet transistors.
Good explanations about working on stuff and how it works.
And what i like about you're way of working, is that you pre-replace diodes, capacitors etc in amplifiers. I have seen many man just replacing faulty ones, or non at all, while the amp is more then 30 years old. I work the same way.
edit: I would have replaced those bias trim pots as well. These are not the most bad ones, but just to be save. Old tranistors are hard to get by these days.
Of i had a high-level piece of equipment like that i would trust you with because I trust your judgement! That's why I love your channel because you do exemplary, thorough work. When you repair a piece of gear you want to make it last another 10 or 20 years! Kudos!
You are genius. As soon as I looked at the schematic i recognized that Nobel but I wouldn't have thought that resistor would burn open.
great side stories make the video better. this is a very interesting machine too.
I appreciate your methodical approach too many bulls in the China shop myself included. I watch you to learn and practice patients and improve my trouble shooting abilities thanks for all you do!
Love the serviceability of that amp.
Thanks for another video Tony, I really enjoy and learn from them. I was in The Hospital Of Special Surgery on East 70th this past Thursday for my Daughters MRI. I said aloud to myself, gee I wonder if Tony worked on these machines, and my daughter asked who's that? I started explaining and she laughed. I am looking to get myself in some sort of school for electronics to do better troubleshooting and understanding my scope and other equipment. Your stories are just fine, my youngest Daughter herself was born in a pool in my living room in Washington Heights
I have a realistic MPA-100. It is very rare and is 100 watts a side. Not an integrated amp only 1 input but has built in EQ/digital VU meters on front face. It is a truly amazing amp.
Another great restoration Tony! Thank you for all your efforts teaching us this year!! MERRY CHRISTMAS to you and yours! Happy Holidays.
No! No just meat and potatoes. Follow-up and background story is also very important. I like your videos. Very much. Not just from the learning point of view. Keep them coming. Thank you very much for this amazing content you're putting out.
xraytonyb: O, my God! I am reading a magazine with receivers, the most modern amplifiers and other audio. But this receiver is much more beautiful than most of the modern equipment!
I had the STA-2250 and it would rock...and sound so good...I believe it was made after your receiver ....and I got it new in 1980, along with RS T110 tower speakers which sounded ok....
All of the receivers you mention in the video were manufactured by Tandy Electronics. They were an excellent manufacturer, and were contracted to produce the Quadraflex and Concept line of receivers for Pacific Audio. The dual mono Concept 16.5 may be the best ever.
I remember when Hitachi first released those Mosfets and the circuit they initially designed to run them. Many companies used this design without much modification. It was ok, but was soon improved upon, including by Hitachi themselves on their MK2 version of their HMA7500 power amp. You should really use anti static precautions when handling them. Thanks for another instructive video.
definitely don't listen to the people in the comments your videos wouldn't be the same if there wasn't any commentary. I don't think i would have been able to learn as much as i have if you did your content "wham bam thank you ma'am " style
you do a great job tony .you inspired me to repair vintage audio thank you for that
DAZZA
Thanks for the info on testing the MosFets , I’ve never heard of the method👍
A couple years late, but the power switch is available on eBay. Look for "Alps SDU3P". Costs about 25.00
Really enjoyed this.
He teaching my dumb as s skills, Arthur. I try to collect as many as I can over the years. I learn a few things every day but I've never seemed to learn it all yet.
Just noted the wire wrap - excellent!
Another fine video. Thanks so much for sharing the audio equipment videos. God bless you and your family and keep you safe. Good holiday season to you and yours too.
I picked up this fantastic receiver two years ago and love the sound it puts out. Outstanding work ! If you’re interested in some work? Love to get it refurbished
Very wise on the no power up those caps could be hiding some nasty surprises Happy holidays! And keep talking I listen more than I watch and it IS your video do it YOUR WAY!
Hi tony nice to see the old Simpson meter,used to have one when I was servicing tv’s many years ago along with my avo 8
Really Enjoy The Video's how you go over things Well done
Been looking for some tweakability in the schematics. Here's what I found:
1. Yep, it wouldn't be an early PLL synthesizer if it didn't have a 100k resistor on the VCO tuning diode (R13). That's 40 nV/sqrt(Hz) of finest thermal noise right there that'll be modulating your VCO, increasing phase noise and hence audio noise floor. Try, I dunno, 3.3k + 3.3..10 µH instead.
2. I would also whack an electrolytic on the 78L05 output on the prescaler board, probably on the backside as it's so cramped... pretty much as much as you can make fit. There's only a 10n there so staggering two different values (like 10µ + 220µ) may be required to avoid problems with parasitic inductance.
3. Like most anything from the time, this unit is lacking FM RF or IF AGC, and the IF strip is a typical Japanese limiter-amplifier job of excessive gain and poor linearity _(screw those textbooks! we want better quieting!)._ However, RF amp MOSFET G2 is easily accessible via terminal 4 on the frontend board, so one could build something there with some extra circuitry. Maybe like this - www.ham-radio.com/k6sti/rfagc.htm - but possibly with some extra pull-up as the MOSFET doesn't seem to be run quite that hot here, looks like ~4 V on G2.
A *lot* of effort has gone into cleaning up the supply rails in this one, with low-noise regulators followed by RC filtering. (This reminds me of another house brand receiver I've seen recently, a (JC Penney) MCS 3248.) Unfortunately, output noise floor is still going to be only so-so, with an SNR of around 95-96 dB - intrinsic noise floor of the preamp isn't particularly low, and total gain at ~45.7 dB is around 2 dB more than it really needs. Not bad for the day and OK on normal sensitivity speakers, but I definitely wouldn't run Klipschorns without a 12-20 dB attenuator between Pre-Out and Main In!
4. Noise could be reduced a good bit in Tone Defeat mode, at the cost of somewhat increased loading on the preamp output (and hence a bit more distortion). Replace R621 (56k) by 22k, and either R623 or R625 by 4.7k. This should bring SNR up to 99 dB. About 3.5 dB less noise (including 1.5 dB as a result of reduced gain) is pretty decent. If you're really fussy about this stuff, you can always connect a good preamp externally between Tape Out and Main In. Power amp noise levels should be very low.
Wow thanks for the link. VERY interesting, i tought that phenomena had to do with crossover distortion.
How Do I get in touch with you about the STA-2200 ?
The STA-2200 was Radio Shack's first and only MOSFET receiver. But it was the second model they manufactured. The Pacific Stereo Quadraflex Reference 650FET R was manufactured by Tandy Electronics a couple of years earlier, and was the first receiver to use the Hitachi MOSFET outputs. Rumor has it the STA-2200 was heavily influenced by the 650FET R. Would love to see a comparison of the two.
i wouldn't call it influenced, i would call it an updated version. my 650fet has a few things going for it over the sta2200. black face. analog tuner. dc offset adjustment.
Cool! I got one of these. Also the 2290, 2080, 2250, 2000 lol. Had to replace that same switch in a couple of them. Its on ebay for 25.00
I was a young, dumb kid at one time myself. I knew everything though. You soon learn to keep your mouth shut and your ears open. Wisdom!
Thanks a lot! Waiting for part 2.
This is way late, like 5 years late. B.ut the issue about TO-3 packages is that the case is the Collector on bipolar transistors, and it is called Drain on Mosfets. That is, whether N-channel or P-channel. Another conclusion I have is that the idea for the 9-V battery was expected to support the clock and station memory just over any short time power failures. Maybe the designers imagined it was related to the small transformer. But yes, it is nuisance, probably part of the main power. No matter, you are right - the battery is out of its “juice” in too short order. Another note, I recall seeing on my unit a note to the effect that the STA 2200 was made by Hitachi.
made by tandy with hitachi mosfets
Merry Christmas Tony!
Very Imformative. Thank you for the post!
Radio shack got a bum rap back in the day for their audio gear. It has stood the test of time. This one is definitely worth putting some time in to restore.
And Radio Shacks ESD protection and shipping is second to none!
Thanks for all the superb videos Tony. I’ve enjoyed watching and learning this year. Merry Christmas and Happy New Year to you and your family.
Runs on Spartan FPGA and has pretty decent TI front end amps too! Nothing to brag about but does it for me 17.5 inch notebook.
Hey there bud, I figure its high time I vocalize much I enjoy your videos...Feel like I'm gaining tech wisdom through osmosis. The story you told us about how your dad essentially paid for his own birth hit me right in the feels, that you'd share such a personal anecdote with us idiots. Keep up the great work and thank you for your dedication!
Wishing you a very Happy Birthday, Christmas and New Year! Andy UK.
I like your family stories.
Wow! I must have one of these amps!
I still have a bunch of Hitachi 2SK134 2SJ49 that I got for my Halfler DH-200. It looks like the power amps are similar. Interesting.
I always straighten out the caps and other bent components too.
As far as my experience and data sheets of American MOS-FETs in TO-3 package indicate, the case is always the Drain. I am not sure about possible difference in Japanese parts. I thought I would just open my STA 2200 service manual and check. But now I cannot find it anywhere...
Anyway, my unit has two problems. The various pushbutton switches are in need of cleaning and probably (but not finally verified), for same switch issues - on power up it often starts chattering the safety relay. One of these days I’ll take it open again. My previous attempts have led to a loop containing the safety relay circuit, the phase lock circuit and a bunch of those switches.
Its an amplifier that want's to be an amateur radio transmitter when it grows up ! its just practicing a little out of band for the 80 and 40 meter bands :-) :-) Have a Merry Christmas and a Happy New Year !! John Bellas KC2UVN
I like the videos where you talk a lot, you have some lovely stories, Merry Xmas.
That's a fine clean sine wave for a noise signal.
I have a cheap OWON US B VDS1022I bandwidth 25MHz. Good enough for audio work and the "I" stands for optical isolation on US B line.
Merry Christmas to you too!!!
I LOVE mosfe t amps.
I was taught that a cap directly across a switch was a no-no. Closing a switch on a charged cap will do not the contacts any favors. You'd need a series resistance high enough to limit the surge current to what the switch can handle. The first set of contacts are already burned. I'm guessing the cap is there to protect the switch when it interrupts the current to the transformer. I'd look for another way to address that problem.
Just keep talking Tony. One rule of broadcasting is to never have more than 10 seconds of dead air. People learn and take in information by narration and not just watching. If people don't want to hear, then they have a volume control.
That unit seems to have plugin modules, I love watching these videos and I hope that you have a Happy and Prosperous New Year, would it be possible to 4.43MHZ Notch filters in before the power stage to try and notch out the oscillations that might happen on either channel.
great video I have the STA 2000 is little bit over bass ,but sound pretty god
That Elba cap IS incredible for its age, but for now much longer. The day after tom?
Nice Amp and its a realistic!!!
this is great! so that glue is from the capacitor... and that will happen if you use the amp too much of if you dont use it, or only because it is old? Cheers!
I own one an use speaker wire to try an get fm channels but stuck on same station digital read out moves but a lot of static , should I clean its buttons. I’m lost all else work an loud as hello
That's why YOU make the BIG BUCKS!
You are killing me with the one-liners! HAHAHAHAHA! WOW! Can I use those?
My display is really tired. People would plug these in for years on end and with that clock built in.. I keep searching ebay for a AM FM clock radio with a compatible VFD that could replace it. No luck so far.
If you like MOSFET amps, have you any experience with Pass amplifiers? Maybe try and get one for repair, I've heard great things about them. I've seen a kit of a Pass Aleph 3 ripoff on Ebay so could be a fun video to make one. Very cheap (about £30 for a stereo pair) although the expense will be the transformer and heatsinks. May get one to try even though it may be complete Chinesium...
Same switch in the 2100 also, both mine are bad.
Same type of switch that goes bad in the sanyo plus series power amp!!!!!!
Maybe give the kit a try Moonbrony! There's a full moon tonight!
Who made these amps, Tony? Thanks Moonbrony.
Assuming you could afford a suitably sized unit Would you consider it worth it to use an ultrasonic cleaner to clean the crap off these boards?
Hello, I wanted to ask where he downloads the schematics to the amplifiers, thank you
I have a STA-2100, actually 2 of them. Do you know where I can get schematics for one?
What data acquisition software package are you running on the PC?
You slated me the b-say jokes, tony. Tony tony
Just cur. How many hours spent in the sta 2200 for the full recapping?
I just bought one these , working, on EBay. Trying to estimate the shop cost for this unit. I'm no electronic tech. Great Video, Thanks
If just replacing caps, you could do it in about 2 or 3 hours.
Tony. Noted the wire wrap. Did wire wraps provide as good as a connection as a good old regular mechanical ones with solder? Also, is wire wrap used any more? Thanks, and keep them coming. Len
They were a more secure method more commonly used than plugs in that era of electronics construction. It likely had something to do with costs of wave soldering or extra processes commonly involved when having to use plugs and other stuff.
Used quite a bit in telecom.
Bias. Where do you get 50mV? is there a rule of thumb standard for all AB amplifiers somewhere?
Nope there is no rule of thumb, correct bias voltage and where to measure it is always pointed out in the service manual.
Never touch the gate of a MOSFET with your finger; the human body can easily accumulate 400-800 volts of static charge without even feeling it - that’ll blow the daylights out of the gate dielectric! And if it gets to the point where you do feel the static electricity, or you see the little spark, you’re talking several kilovolts at least! The dielectric strength of (dry) air is about 10 kV/cm, so 1 kilovolt can jump a 1 mm gap. Instead, hook an insulated clip to the gate, then clip the + (red) lead from the meter to the drain, and the - (Black) lead to the source. Now touch the other end of the clip lead from the gate to either the source or drain; source=off for enhancement-mode, and drain=on for enhancement-mode! Finally, you can wire a 1k pot between the source and drain, and connect the center (wiper) of the pot to the gate; you can now observe the MOSFET in action as you adjust the pot. HTH!
Also, (note to viewers) never test a line-powered device with line-powered test equipment (such as a scope, frequency counter, spectrum analyzer, etc...) without an isolation transformer, or without verifying that the power transformer in the DUT (device under test) is not shorted primary-to-case, or primary-to-secondary! Failure to observe this can result in your test equipment becoming an expensive paperweight, or the DUT can even be damaged or destroyed!
Also, they need to make sure that their isolation transformer output is really isolated.
If you're holding the body of the MOSFET, which is the source, its fine to also handle the gate. But you should never touch only the gate electrode, that's asking for it. Nylon carpets and clothing have no place in an electronics lab in my opinion, so much static with that stuff.
I have the same receiver, somewhere. LOL It is a great unit, but ugly. Yes digital tuning just came out. The battery backs up the computer to hold the presets.
US B scope is great for demo.
where does the Dolby come in?
Appreciate the full story in these videos but do watch at x1.75 :o)
is your friend who has this same model Bill Carlin, he was born in green bay wi then moved to calif?
Also (for enhancement-mode MOSFETs), you can tell if it’s N-channel or P-channel by measuring from source-to-drain. If you hook source to - (black) and drain to + (red) and you get high resistance you have N-channel. If you get a low resistance, you’re reading the body diode of a P-channel device. Likewise, if you hook source to + (red) and drain to - (black) and you get high resistance, you have P-channel, and if you read low resistance, you’re seeing the body diode of an N-channel device! This should work for all enhancement-mode MOSFETs, but may not work for JFETs.
My Peak Atlas DCA75 Pro has spoiled me...
I just remembered I should pay the midwife. Great story!
God you're busting my guts!
Beenhead! You don't know me dude! Just watch the master! Nobody is talking to you!
Still just a piece of Japanese stuff; nothing compared to my Realistic STA-250 (built in America by Sylvania, circa 1973) , I drove it very hard over the years (and in college) and nothing ever blew up on it; maybe just having to replace some pilot lamps.
Every time I get of my car during very dry, cold weather, I drag my butt across the seat and get zapped! No kidding guys and gals it hurts. That's several thousand volts. I've been an industrial electronics 're h for 30 years and have been shocked many times by 120, 277, 480, and 600 volts ac. These were partial encounters through high resistance barriers (my brain). Those dc static shocks HURT like hell!
Get a Shaxon anti-static wristband. Wearing it without the ground tether will keep you from getting zapped. I wear mine every winter and it works for me. And don't listen to the naysayers, just try it.
You think some of that site off on you, Tony? I do!
New England. Oooook!
Review?
Just wrote it down man!
You can always toss a wire antenna to a tree and start DXing on 5MHZ band...
similar a kenwood kr 9050