0:15 Intro 2:36 First look at the 382b 7:09 Opening the unit up and taking a look inside 12:42 Testing the output transistors 14:41 The Sencore Cricket tester 20:35 First power-up / checking the power supply 26:03 Checking speaker output capacitors for shorts & ESR 27:45 Connecting speakers and sound check - There is noticeable background hiss! 30:11 Playing some music - doesn't sound too bad (after Tony remembers to remove the current limiting) :) 31:39 Checking to see if the tuner works 34:59 Troubleshooting and repairing the background hiss problem using a unique troubleshooting method 50:06 Taking a look at the MPX stereo issue 54:59 Using X-Y mode on scope to view/align stereo separation in MPX circuit 59:00 Had to replace a few components on the MPX board 1:01:08 The MPX board in this unit is different from the one in the service manual!!! 1:02:25 Touching up the alignment of the MPX board after replacing components 1:11:17 Loose connection on transistor socket of tuner front end board 1:13:27 Experiments with the Power supply filter capacitor 1:30:58 Testing the output capacitors for proper frequency response and output
It's 100% designed anf manufatured in New York at Zenith . Manufacturing only could also have been, in Milwaukee or Detroit. In the order! Everything everybit and part of this receiver is 100% designed and manufactured in the States. Exept for some caps and resistors maybe (from the UK or France very likely).
Thanks for another wonderful video. :) This one helped me better solidify my understanding of testing transistors, calculating RC filters and speaker coupling!
Older electrolytic caps in a lot of audio gear (I have some Dynaco stuff) have a marked designation of "WVDC" the "W" being the working, or expected operating voltage. I'm sure they were designed to have a max rating at least 20% higher to account for ripple and some aging. I was thinking the same thing about the outlet coupling capacitors and the larger fuses, as long as the capacitors were working properly, they would not pass DC to the speakers to the point where they would make a driver fail, so like you demonstrated, a driver such as woofer that had no series crossover cap in its path would take a small amount of DC until the coupling caps charged. 1:19:30 was a great demo of checking power supply ripple, and also testing to see if a larger cap value will be beneficial! Using a 2 channel scope and setting one channel for AC coupling at a lower value is a good tool for checking for ripple as you check for DC voltage level as well. Good stuff 👍
For years I've been trying to recall the stereo I had as a kid. I kept describing it as having black and chrome knobs and a meter on the right!. Then here comes your video and I almost fell over! I don't think this receiver is the one I had, but mine looked very similar from what I recall. And you're right, it sounded amazing. I had a pair of those Zenith Allegro speakers connected. To me it was the best sounding system ever! And I think my dad just threw it in the garbage when they bought me the Pioneer SX-60. Which also sounded really good for what it was.
Great troubleshooting tip with the signal tracer on the power rails! Watching on my phone, I initially thought the main 50V rail was regulated, hence the relatively small main reservoir capacitor. Some amplifiers do use regulated supplies for the output stages but it's not that common because "dynamic power" is the same as "continuous power" as there's no rail sag. This fault and the experiments at the end were also a really important demonstration to show how critical the power supply is for overall performance in some cases, yet not in others.
There is a stereo switchover adjustment shown in the manual - made a huge difference on one I worked on recently. No longer needs a strong signal to switch over to stereo.
When I was growing up my next door neighbor was a real audiophile and he built that exact Scottkit 60 integrated amp and you could hear him thumping it every now and then.. As a young kid who was into sound it was very impressive, and when I was a young teen he sold it to me cheap and I used it for a while.. He told me to remember to turn the volume all the way down before you turn it on because it really thumps the woofers when you first turn it on,,, and it did !! I didn't have it very long before it lost a channel and that was the end of it... He's almost 90 now and I talked to him a few days ago,,, still sharp.
Good Job, Tony. few years ago, I fight and learned a lot from 382B. my MPX board is same as your, 5 Trs and small can type coils. Scott 348b has proper MPX schematic, and also instruced how to mod from 4Trs version into 5Trs MPX-14. The long fight is mainly on MPX, there is no Stereo separation and no Stereo light, since Q3 is never switch ON, after tweek R22 , then I got stereo FM, sounds good.
12voltvids just repaired a Fisher 170 receiver from 1973. The circuit boards were outsourced to Japan and were completed as subassemblies by Hitachi. They were shipped back to the USA and the rest was assembled in the states. I am almost certain this was going on in that time period by many manufactures in the USA.
These units were some of the very first solid state "audiophile" grade stereo components. I remember seeing them at "E. J. Korvettes". The 2N3055's were also used in the Dynaco 120 Power Amp, which has at least one "re-build shrine" web site for it. I regret selling mine.
Korvettes, must be from the NE. I had one of their XAM house brand table radios when growing up. Got me interested in electronics. I took the rear cover off and "adjusted "all the pots. Took my dad weeks to get it to somewhat play music again.
Super cool, I'm working on a 342 that I got for the cost of a 6 pack in rough shape. Bur great to practice and learn. Missing the fuse caps, so I added that and some deoxit and is making sound again. The slight pop, when first power on also a low volume channel. Your videos are ridiculously long, as they should be because this kind of work is not a 10 minute video. Keep up the awesome work.
I built one of those LK60 (not the B version you show) Scott kits in 1968 or 1969, with the wood case. Worked great. I might still have it around somewhere. Last time I tried it, the controls were pretty scratchy.
Hey Tony, regarding your last segment in this video: I just bought a *really* nice example of a 382-B, and whaddya know, sitting right after the rectifiers is the originbal "TENNESSEE ELECTRONICS" cap (their ad slogan should've been "THE ALL-CAPS CAP!"). So, guess what the value is? 1,000µF. After seeing that nearly *every* electrolytic in the amp is a Callins/ Tennessee Electronics, my heart sank a bit. However, fairly surprisingly, after I tested the outputs and checked for DC sitting on them, I put it on the dim-bulb and it fired right up, turned on, tuned in, and hasn't dropped out yet! I'm pretty amazed. And sure enough, you were right: the amp sounds wonderful.
Glad to hear things are crazy at work, that hopefully means you and your crew are staying ahead of inflation and some left over for more test equipment for the lab.
I have a Scott 342B that I did an electronic restoration on maybe a year or two ago. It worked great on the original caps, but mine was a much earlier revision and used the epoxy type radial electrolytic caps. I ended recapping with Nichicon Fine Gold caps. I also replaced the output coupling caps with 2200 MFD caps. I probably should go back and up the filter capacitor to a 4700 MFD cap to allow for the better power handing. I had issues with the tuner on my 342B as well. My issue was a broken wire in one of the IF cans. Once I opened up the can and repaired the break, the tuner worked really well. I was getting FM stereo, but the lamp wouldn't come on to indicate stereo reception. Ended up I had the incorrect lamp in place. I'm curious if yours is a late issue receiver and if it uses the same multiplex board as the 342C variant. The 342C is a very different animal all together while the 342 original and 342B are pretty much the same. The 342 original lacks the regulated power supply so the center point has to be set via an additional set of pots on the amp board. The meters tend to be failure prone on these units. Most commonly in the 342 original. They are normal stuck where they last worked as the coil springs fail in them. With the right speakers, 18 Watt per channel can go quite far. I also have the LK-60B amp as well plus many other Scott receivers, amps, and tuners.
The other problem with making the (filter) caps bigger is inrush current. Maybe Tony can put an ammeter in the circuit between the bridge rectifier and the cap to show the effects of capacitor size vs. inrush current. 😌
One thing I learned what I did not experience yet: hiss from a power supply. You can make it even visible by showing both channels on max. volume on the scope, and see that the form of the noise is equal on both channels, giving the source away. And when you showed the schematics at the beginning of the video, far before you mentioned the filter cap, I reacted on the value of that cap to be remarkably low with 1000µF. I have seen a few, but not so low. I have a Marantz here, 2 x 12.5 Watt at 8Ω, and it uses 4700µF, with 2200µF as coupling caps. I would upgrade yours :)
Amazing: amp to speakers to microphone to youtube processing to my PC speakers, and I'm still getting booming bass and an overall nice sound. I don't know if that's good or bad, when it comes to your hobby. :-)
Great video Tony 👍 I know you already put a lot into it but it would have been interesting to see some distortion sweeps from 20Hz to 20KHz with the different levels of decoupling on the supply at say half power, to see what the PSRR of the amp is like at normal use, I.e not near clipping.
I have what appears to be the older version of that Fnirsi oscilloscope, yeah it ain't perfect but for the money, it's actually pretty good! Being battery operated, no need to worry about earth loops and isolation transformers....
Nice work on this Scott receiver, Tony. The "B" series was never my favorite. Many from this time period (1967-68) had that crummy Japanese-made multiplex adaptor, and they are universally terrible. I have no idea why Scott chose to install these sub-par adaptors in many of their receivers around this time. One other point: I'm pretty sure that the coupling capacitor in the amplifier stage is 500 uf, not 1000 uf. Interestingly, the follow-up receiver in this series (342C/382C) is a complete redesign, and is superior in every way to the receiver that you had a look at. The "C" series are complementary output, and have newly designed circuits everywhere else, as well. However, the basic receiver that you examined was manufactured by Scott to the very end; the final iteration being the 357 in 1972.
Hey Tony. I'm working on a Fisher 80R right now. I got an FM transmitter that I can connect my phone to and transmit royalty-free music over the air at various frequencies. You ought to get one of those. It was like $20. I want to find one for AM as well.
Just get a fl2k adapter and make your own private AM and FM broadcasts at home. It will cover the entire AM and FM bands and then some. In short, you can have it play many different tracks at various frequencies.
L-R means 180 degrees out of phase, hence complete cancellation. You were right the first time. 90 degree angle on the scope in XY mode is irrelevant to the phase. It is determined by the physical construction of the scope.
You are incorrect. Watch the video again. X-Y mode is very relevant for setting up the MPX circuit. In XY mode, one channel deflects the trace in the vertical axis and the other channel deflects the trace in the horizontal axis. Connecting the L & R outputs of the amplifier to channel 1 & 2 of the scope will give the following results: When the MPX generator is set to Mono, Stereo or L+R, you will get a 45 degree sloped line that varies in length with amplitude. Both channels are in phase with one another. When the MPX generator is set to L-R, the line will slope 45 degrees in the opposite direction. The difference between the +45 degree and -45 degree line is 90 degrees. This is what I was talking about. When the MPX generator is set to Left only, you will get a vertical line (provided you are connected to the Y channel) When the MPX generator is set to Right only, you will get a horizontal line (provided it is connected to the X channel) If the line is not perfectly horizontal or vertical when only R or L is selected, it means that the separation is out of alignment. This is a very easy way to see the relationship between L & R channels when doing your alignment.
I am not incorrect. You got two lines on the scope at 90 degrees in XY mode, indicating a 180 degree phase shift between the actual sine waves. Look at them on the scope. If it wasn't 180 degrees there wouldn't be full cancellation. Take a look at both sine waves at the same time and see for yourself.
I never would have guessed that high frequency white noise would be generated by the power supply. Aren't there high frequency bypass caps that would have snubbed that away? There were some small caps across the secondary windings of the power transformer, but that is probably for the switching noise of the diodes, just guessing, not part of the regulated supply.
Any suggestions on what zener diode to use on the power supply board? It would be for a Stereomaster 367 which has a power supply similar to the 382b. Part number is D401. I have the exact same hiss that xraytonyb has.
Tony - I noticed you rebuilt a Kenwood KR-6050 receiver a few years back. I'm thinking of getting the 6050 or 7050 for the awesome FM reception they have. It appears they match the reception and specs of the great Kenwood KT-7500 tuner. As far as sound quality and build quality, are these years of Kenwood receivers as good as the 1977-1980 Pioneer and Marantz receivers?
Awesome vid Tony! I have a 50 yr old cap coupled receiver and it also 'pops" when first turned on. Not looking to blow up my speakers if something went wrong, I bought one of those $9.00 chinease speaker protection relay circuits. It's mounted in a box along with a 12 Vac transformer. Wired up speaker terminals and inputs. Connected to the switched ac port, it turns on with 3 second delay of the relay. This has stopped the pop noise, but how? If the caps have to charge up, wouldn't it still pop when the relay closes. Also noticed during the ripple experiment, the ripple sine wave has little ripple lines that seem to match the 1000 hZ signal, is that possible?
The voltage on negative side of the output capacitor is NOT equal to the positive side when the capacitor is fully charged. If it is, the capacitor is shorted!
So by increasing the filter cap to the point it causes the transformer to sag, would this be detrimental or shorten the life of the transformer? There by defeating any advantage of increasing the filter cap?
Increasing the value reduces the transformer conduction angle, which raises the peak current draw from the transformer and increases the magnetic effects. You need to be sure the transformer can handle it. 1000uF is about 1/4 the value I would expect here at this vintage, but the power transformer is also smaller than expected. Care required. If it sounds OK leave it alone.
Cheap little dollar store / thrift store bluetooth speakers might be easy to modify into a workable signal tracer, as long as they're not noisy. That might make a decent RU-vid video, actually.
Hi Mr. TonyB, I got to this video as I am currently trying to bring to full life A HH Scott 357 receiver and I hope you could help me with a advice regarding transistor substitutes. I cant find online any reference to the transistors in the voltage regulating circuit, the 1-003 126 by Power Physics, and 0-008 7130 by W(?). The 357 is open up right now at my coffee table. First, regarding the 4 output transistors you mention in the video, your 3055 seems to be a repair replacement. First, the Scott designated names is printed on the back panel: "QP8 or QP12". In the manual of your model there are two power transistors - OP8 and QP11 (where Q11 is the voltage regulator transistor), listed with their prices as spares. I could not find diagram for the 357 (the 357B has somewhat different design). The 357 has no manual online that I could find, and the voltages and names of the transistors are different from your 382B. The back end transistors are RCA 71352A. Unfortunately, it seems that the early transistor designations didn't transit well into the digital age.
Many of the single rail capacitor coupled outputs in the early days of germanium transistors used a negative rail and PNP transistors. I am not sure why, perhaps the NPN were more expensive, or not as reliable? Someone in the community will know I'm sure.
