Thanks for the shout out and the kind words! I have a few of these in several cabinet versions. You're right these things true to the Zenith name are made very well. I've found problems with static on FM that sounds like SMD Actually is a defect in the slug tuner. Thanks for a glance at the schematic these are strictly thru SAMS. Great sound mod to!
I've heard a lot of table radios where the loudness compensation really improved the sound. Nice sound at normal and quiet levels, and loosing the bass boost at higher levels allowed the radio to fill a large room with clear sound without clipping. But Zenith sure did it wrong on these. Killed the treble along with the dip in midrange.
Very interesting about the tone mod, I'll have to remember that. About electrolytics; the old ones had a healthy surge rating, the new ones don't...and I've measured as high as 190v surge on a 160v cap. I use 250v nowadays, just for a little added safety margin.
Power enters the output transformer at Y. Some current flows to the plate of the 35C5 and the rest of the current out to Z in opposing direction on the winding. This would help kill hum and remove some of the DC bias on the transformer core.
Hello Shango I have a Crosley E15SL and its the best sounding table radio I have in my collection. You repaired a white model that was missing knobs. That Crosley had a tone tap like this Zenith but Crosley used different values and attenuated midrange and passes treble and bass. You're a great entertainer to watch you on Radio and TV repair and I have this game I play and guess what I think might be wrong during your diagnosis thanks again Ace 👍
Love the old radio's, they were my escape when I was a kid, we were dirt poor, my aunt gave me an old tube radio when I was at their farm working cattle one year, I put that beside my bed and late at night, I would play that radio loud enough so I didn't have to listen to my parents fight, man I can still recall listening to KOMA where the "good guy's" played all the latest rock and roll! Bismarck had Padre's Platters another rock played by a Catholic Priest. I still have that first transistor radio, mom saved it for me, and returned it about ten years ago, an old Jade 10 transistor...
The capacitor values are both 24pF for “L10,” it’s identical “L8” according to my similar schematic of an X334 Zenith. I know this video has been out for years but I along with many other reference your videos for new repairs/restores that come along. I am now going to make the fidelity upgrade on my X334 as the values are identical.
Zenith in my opinion built the best AM-FM table radios in the tube era. My favorite is the 845C with a 7 inch round speaker and a tweeter. It has a true tone control not just a treble cut. I've had one beside my chair for over 30 years. I have one that looks like your plastic set but it's FM only, be interesting to see if it has that capacitor.
When I found one of these radios a few years back,I was curious about the dot on the dial around the 100 Mhz mark. It's not a CONELRAD mark but marks the Zenith owned Classical FM station WEFM 99.5. Thanks for the fidelity mod, FM should never sound that muddy.. Stations these days have over processed and compressed audio as it is in the loudness wars, that cap makes it worse.
It's wild how that cap being removed doesn't hurt the bass at all, it only makes the treble come back. I have no idea why they would design that in there, I wonder if that's how it was meant to sound or if something (on all of them?) has changed over the years?
Looking at that makes one feel that the original workers must've taken great pride in their work. That is, long before Zenith was forced to move production to Mexico & the Far East. And incidentally, I have a sealed Zenith-branded 9v alkaline battery in front of me (brother found it somewhere). It's dated 2016 & has the old "Z" logo on both the battery & the package, and old, "the quality goes in before the name goes on" phrase printed across the latter. But turn it around back & one sees, "Made in PRC." Ironic, yes?
LG (Lucky Goldstar) is the company that did in Zenith. They didn't want to build electronics in the USA. They got all the Zenith technology along with the huge dealer network, which is really what they craved.
I subscribe to Radio Rescue and he is a good guy to watch. Another very talented and very detailed restorer is Restore Old Radios. This fellow does multi-part videos of his restorations that goes into chassis de-rusting, period specific wiring, and cabinet restoration as well.
If you or your viewers ever wondered what that dot is just to the left of the 100 megahertz marking on the FM tuning dial it signifies 99.5 megahertz the frequency of wefm, the nation's oldest FM stations at the time and it was owned by Zenith radio Corporation in Chicago. In its heyday, it was a classical music station in Chicago. I don't know what is on that frequency now as my information is dated as I left Chicago over 40 years ago. That dot was on every Zenith FM radio or radio tuner from 1948 up until the time they started having radios imported from the Orient.
So I got the X318 and I'm very pleased with the heavy bass. I have a longwire FM antenna hooked up to it, and I am pulling in stations 60 to 70 miles away with amazing clarity. (I am picking up 92.9 in Summersville, 105.1 in Saint Albans, 105.9 in Huntington, 103.7 in Beckley, and WKAZ-AM's low-powered FM repeater on 95.7.) AM reception is okay, but I mainly bought this for FM.
All Zenith FM sets are slug tuned. The later AM/FM tube sets like yours had no tone control. The earlier sets have tone control, and some even have a small tweeter with a crossover! I enjoy watching "Radio Rescue" vids as well! Good stuff! Alexa, can you test the tubes in my Zenith! lol
just got done fixing an old radio i have had when i was 10or 11 a model 628 1145 jcpenney radio ..cleaned up the batt compartment no go ,,get out the cap tester well i replace all caps plays great ..an it played last time i used it ..easy fix ..love your vids you are one sharp kid keep it up
I'm working on a similar Zenith AM-FM radio, model 7N07, which has a tweeter. It has the same sequence of 14GT8 -> 100K resistor -> .001 capacitor -> ground. I haven't gotten mine working yet, but when I get it working I'll see how it performs with and without deleting the .001 capacitor. Possibly Zenith optimized for the tweeter and not for radios without it. Maybe so that people doing a side comparison in a store would buy the more expensive radio?
The low high end reminds me of something retrochad (I think) demonstrated with a jukebox he had where it was designed to cut down the high end as the volume control was turned down. I think it was probably so the music could be present, let's say in a diner, and so people could understand the conversations the where having with each other, since the high end in their voice could be heard over the music. This is just my guess.
Dude - you're a hero. I have an X316 and the muddy sound was driving me nuts trying to listen to it, so I boxed it up and put in in the garage. Just got it back out and I'm gonna fix the sound tomorrow! Thanks for getting to the bottom of this!
The bass/low end was a gimmick of sorts, gave the radio a higher quality sound over the Japanese sets showing up around that time. Zeniths were always noted for plenty of low end on many of their mid-upper end radios. And as another commenter eluded to, it lessened listener fatigue over longer periods. Now as for AM sounding different, you have to remember that AM stations were putting out 10khz audio bandwidth when this rig was built. Today, most AM's are outputting 6khz audio bandwidth on non-HD stations, 4.5khz analog bandwidth for stations running HD. Big difference.
The green capacitor is the "balancing capacitor" in the FM ratio detector circuit. [I stand corrected; the detector is a Foster-Seeley design here.] These radios remind me a lot of a Japanese-built Lloyd's radio I have. The dial design is almost identical. However, mine has two 12DT8s (dual triode, very similar to 12AT7) in the FM front end, whereas yours seems to only have one. The Lloyd's radio also uses conventional variable capacitor tuning on FM, rather than slugs. I suspect that the slug tuner would be less susceptible to microphonics than a variable capacitor.
FM stations in the USA use a pre-emphasis circuit with 75 microsecond time constant. The idea is to boost the high frequencies prior to transmission to improve the signal to noise ratio. At the receiver, a 75 microsecond time constant de-emphasis circuit is used to compensate and flatten the end to end frequency response. R29 and C28 appear to be that de-emphasis circuit. I think the problem is the relatively large speaker with good bass response but the lack of a tweeter. The high end frequency response is poor. Removing the de-emphasis circuit increases the amplitude of the high frequency content at the speaker and improves the overall frequency response.
That with the output transformer is not a filter choke ruther it's against core saturation. In this way you can use a smaller iron core for the output transformer and you have better base response.
To me, it is pure magic.. still I got a radio to play with, it has a cats eye like a end of 40's to 50's radio and a newer plywood box. As it is semi wrecked, I love a clear acrylic cover on it. It was restored at amateur level as part of the capacitors were replaced but some paper ones did stay behind... the cord was cut off and given to me. Where to start I think...
Arjan Wilbie I’m in the same position as well with a old 1955 radio with 5 tubes. Cord is missing as it’s been cut or chewed off, have no equipment to test the caps or tubes! Mine looks all original too with a lot of those wax caps.
My father had that same radio on his kitchen table until he moved in 1976. He would listen to country western music on it. Not the kind of well produced country you hear these days but the real classics. Willie Nelson when he was clean shaven with short hair. Merle Haggard. Tammy Wynette. George Jones. Buck Owens.
every radio of that vintage seems like the high freq was a problem. I wonder if broadcast standards or even the kind of music or pre emphasis have changed? or maybe they were worried about stereo noise.
That's what I'm wondering, I've seen loads of recommendations to lift certain caps in these radios in order to open up the frequency range, the standard of the time must have been for bass heavy and treble light audio... as Shango066 would say... "who knows, who knows."
I concur with your view on the working voltage of replacement electrolytic capacitors. I have 'rebuilt' switch mode TV power supplies using a 240V AC (Australia) mains supply, then rectified to say, 345V DC as the 'hot' side, where the critical regulating components contain 25 WV electrolytics, generally coupled to the 'chopper' transistor. I made it a habit to match the manufacturer's working voltage, as well as the extra (small) expense in fitting low ESR types, and not too close to the heat sink.. The (original) main problem is loss of voltage regulation when the electrolytic goes low in capacitance (also at a low temperature) causing the chopper transistor to short.. ..followed by fusible resistors/fuses...
Hey,Shango. I know this is an old video. But great fix. Question for you. You said that it sounded like there was SMD developing in this radio. Can you show how to solve/ fix that? I know you would have to either install a new or good IF transformers or actually fix it by adding some caps. The question I have is what size caps do you use to fix the SMD?
Ratio detector vs discriminator - Eugene McDonald (head of Zenith) refused to use the ratio detector because it was RCA's answer to keep from having to pay royalties to Edwin Armstrong, the inventor of wide-band FM broadcasting. IIRC earlier Zenith FM radios advertised using the 'Armstrong circuit'. David Sarnoff was particularly vicious to Armstrong who ended up committing suicide over it.
Why the audio output transformer has a tapped primary: That transformer has DC flowing in its primary, which produces static magnetic flux in its core. To keep the core from saturating, the transformer has a larger core and air gap than it would need if there were no DC. By tapping the primary and having DC flow in the opposite direction in that second section of the primary (31:55), some of the static flux is cancelled, so a smaller transformer can be used. (Some power supply hum is also cancelled.) However, to this arrangement's disadvantage, some of the audio signal is delivered to R40, diverting audio power that could be delivered to the speaker. Some AA5 radios also have the tapped audio output transformer, but, probably, most of them don't. You should be able to substitute an audio output transformer with two wires to its primary, connecting the Y (red) and Z (blue) wires together to one terminal on the primary and brown wire to the other terminal. If the replacement transformer's impedances properly match those of the output tube and speaker, the volume control should produce the same audio loudness at a lower setting.
There are some of us who love the bass. Guess I am among those, well I was until the VA gave me a set of hearing aides and I could hear all the highs that I had before going on my all expense paid 13 month vacation in The Republic of Vietnam.
With the filter capacitors, do you think the working voltage should exceed that of the old capacitors by a small amount? How true is it that older capacitors had a lot more of a working voltage tolerance window than new capacitors? So if it's a 150V cap you should replace it with a 200V ? Isn't the initial surge voltage somewhat higher than the "settled" working voltage?
you're quite right about cap voltage, if using one with voltage rating way above what it would be subjected to, it may well not stay formed long term, but too high a capacitance will result in high surge currents, valve/tube rectifiers may be damaged, but others should be ok..
I removed a capacitor from my Philco 48-482 that shunted hf audio from the plate of the output tube directly to ground, had a similar effect and sounds great now
Greetings: Capacitor values: as capacitance value increases, so does initial rectifier current draw. Using an inrush current limiter such as the CL90A may help save tube rectifier life when cap value doubles.
RCAs shunt the high frequency audio too, especially on shortwave bands. I believe my RCA 16X13 has a 4 position switch for source; A is SW with high freq shunted, B is Broadcast with high freq shunted, C is Broadcast not shunted, and D is line in not shunted. I was wondering why my dad drilled a hole in the side of the case to mount a switch (the case was already REALLY rough) turns out it was to cut out that crossover cap. If I ever get to restoring the case I'll relocate the switch to the back.
it's just like the marantz 70's units. the early models had caps rated just above the operating voltage, and the later B models had caps rated just under the operating voltage.
There's probably a reason Zenith played around with the tone of these radios and why it's a little bass heavy. When they were originally manufactured, the FM dial was mostly middle-of-the road pop and "beautiful music" sourced from lp records. The source material didn't have the frequency range of what's on FM today - they were really making them sound good for the type of material that was on FM at the time.
These were commonly seen in homes back in the 60s and early 70s in the kitchen, living room, den, etc. Offices and waiting rooms, even in the small town I grew up in, had Muzak systems. The only businesses where you regularly saw a tabletop radio would be in like a mom and pop garage, cafe, or gas station.
Omg just pulled one similar to these and found that cap that muffles this thing and man does it sound so much better crazy what a lil cap can do for it
Hi I purchased a Zenith X323 On eBay and when It arrived the volume knob was broke off so to bad packaging so I need a new Volume Potentiometer with switch, do you know the make/model number of the Volume Potentiometer, I would rather order it and just take the radio apart once. Thanks Jeff
22:50 That reminds me of the crossovers Magnavox put in some late 1960s Astro-Sonic consoles; they had a resistor in series with the horn tweeters that made them almost impossible to hear, especially the way they were mounted; shorting it out improved the sound a lot. In this case, I wonder if Zenith was worried about the discriminator distorting the high end when the signal got weak, or just the hiss being loud relative to the signal and just figured they'd get less grief with the treble cut out altogether.
Both radios are cute & so basic like my one. It sounds like your cat must of got a hair ball & needed to barf it up. LOL BTW I do prefer your videos nice & long too, even movie length is good as watching You is far better then a movie anyday! :)
I think I know why they have that capacitor in there to take off some of the high end. If you think about it, most music back in the day when that radio was made did not have as much bass, so therefore they probably added that capacitor to make it have more low end.
In regards to the SMD noise, i found that the problem can go away just by playing the radio for a long period of time & putting it into daily use. i have several of these Zeniths & i use them on a weekly basis. the SMD problem went away after a day of use & has not appeared again.
I have a Zenith model N730 (very similar to with same chassis as the one in shango's video above), it initially suffered from SMD like effects which eventually went away with use. AM would cut in and out, and FM performance would come and go. All that cleared up after a few days of use. In the end it needed new filter caps and that was pretty much it. Decent tuning performance on both AM and FM, but it too suffers from the muddy FM sound. It is currently one of my most used tube sets.
31:57 Is that negative feedback through R38? I wonder if the use of the second primary winding is also intended to cancel load induced power supply ripple, though whatever its benefits, I'd also expect it to magnetize the core and make it saturate earlier. Either way, these sets were not intended for waking up the neighbors; FM cuts the normal 50C5 AA5 output in half.
AlexM answered my curiosity about core saturation; seems the DC through the extra winding was intended to cancel the DC through the audio primary (I'd forgotten about that), actually improving the headroom and preventing saturation.
I live in Northeast Ohio. Out of the dozens of radios I've collected over the years, only one ever had Silver Mica Disease in the IF cans. I'm wondering if climate plays a part in the development of SMD?
@@shango066 Thanks for the reply Shango! We have very humid summers, but extremely dry winters here because everything is stored indoors with artificial heat.
Same, said it before and will again. Whether it's a 5 minute update or a 2 hour epic it'll get watched by me multiple times now and into the future. Apart from the entertainment, it's a useful resource to pick up little titbits of knowledge along the way.
So the budget kitchen table top model didn't sound nearly as good as whatever their top shelf deluxe model they were pushing at the time. Or back in the day folks liked Midas muffled sound??? The human ear hasn't changed since than so wtf??
It'd be interesting to see a video on an older "Roberts" radio, these are top notch English made portable radio's, they've been made over here for a good 70 plus year's, no idea if they were exported across the pond or not, but I'd bet there are plenty over in the states
Tone cap.: Best guess, when played very low (think sleeping baby or someone disturbed when it is "too quiet") limited highs make for a more soothing sound when fidelity is secondary .
that was fun, thanks man. what you said about buddy's channel,is how i feel about yours.. thanks for the recommendation tho... Have you ever heard of Rosie Okelly's channel. every now and then she works on vintage audio.
another common problem on these Zeniths is the plate load resistors to the 12DT8 often go out of spec & cause the FM to stop working or do other strange things.
The muffled sound is because people liked that sort of sound back then. Now the broadcasts have so much more compression. I had an English FM only radio that only offered degrees of muffled. It also had a totally dried out Dubilier filter can that left 70 V of ripple on the 230V B+ line. The radio was on a PCB that was toasted badly around the o/p stage. It was at this point I also saw the o/p tube was gassy (pink glow). That turd got EOL'd. Sometimes it just isn't worh wasting your time.
I know this video is old now, but I bet Zenith did that little modification to intentionally make the radio sound flat, and not crisp because at the same time this was on the market, Hi-Fidelity radios and gear was the hot item to have and they wanted to SELL SELL SELL Hi-Fi. Couldn't have the cheap table top radios sounding almost as good as the expensive stuff, so make it sound flat.
