...this evening I began work on my latest acquisition, a Zenith Royal 51-1, chassis 9XT41Z3...

...not what I'm typically interested in with regards to transistor radios, but it was there and it was vintage and it was a Zenith (although a Royal 94 of the same vintage would have been much more to my liking)...so my curiosity was piqued and I brought it home...Zenith was still making good stuff in 1966-67, as suggested by component date codes (latest being 6638)...
...four alkaline AA batteries had been left in it for who knows how long and they had leaked...had to pry them out of the holder and all kinds of crystalline crud fell out when they did...and there was more underneath. First order of business was to strip out the innards to clean out as much as possible...

...there was a lot behind the lower left corner of the front and all over the speaker basket...

...and once I got the speaker unsoldered and removed...

...it's toast. Actually the only thing that was seriously damaged by the leakage. And an original speaker to replace it will probably be difficult to find (will probably need to look for a 'donor')...I'm also going to need to thoroughly clean the external power and earphone jacks as they also have some crud on them...but got the battery holder out and cleaned it thoroughly...a little vinegar dissolved the stuff...
...next, took some Fantastik to the front panel parts. I was able to carefully remove three speed nuts and remove the tuning dial window so I could clean that thoroughly, and also to remove the front grille. Well, seems the battery leakage had affected that as well; not only did the tobacco residue that I expected to find come off, but also some of the finish on that particular corner of the grille...got to figure out how to match the color to try to refinish it. However, the rest of the front panel and the dial window cleaned up very nicely. Next will be to remove the volume and tuning knobs to clean them (they're also tobacco-stained), which is going to involve removing the dial cord (which will be very easy to restring)...

...The tuning dial looks like it's been restrung before, and not with the right kind of cord; there's a lot of play in it. The radio has been repaired before; the FM RF amp transistor was replaced with an early version SK3006 (which is the same size as the audio output transistors and much larger than the original--and probably not the correct type for the application!). However, it was left way off the board and is perilously close to one of the FM front end coils, to the point that its can could short out against it or at the very least interfere with its alignment. The tuning dial drum had to be removed to replace the transistor, which probably explains why it had been restrung. I'll probably have to do it again, because I want to try to reseat that transistor and shorten its leads, and see if I can move it away from that FM coil.
...And I'm sure I'm in for more fun after this; it's got five of those Callins 'firecrackers' in it that I want to replace, as well as a couple of other electrolytics, and it's loaded with half-watt carbon comp resistors which, even in transistor sets, could conceivably have done funny things in 45 years. Not to mention several of those components in the immediate vicinity of the battery holder have deposits on their leads, which could be hiding lead damage. I've got a complete service manual for this so any troubleshooting I might need to do shouldn't be too much of a problem...
...although the chassis number has me scratching my head. The service manual calls this a chassis 9XT41Z3, but the label inside the radio called it a chassis 9XT4123...could be a typo, I suppose (someone mistook the Z for a 2 when printing the label)...
...anyway, the radio looks reasonably well-built (it is a US-built Zenith, after all) and is quite heavy for its size; be interesting to see what it sounds like and how it performs when and if everything is in proper working order (even if I have to settle for a non-original speaker)...

Where did you pick up the radio? It's too bad that the set was in such a shape.

I have two of 'em; reasonably good receivers, and I haven't done any restoration as yet.

speakers everywhere without even looking. looks like 2" alnico you got there. doesnt need to be alnico thats just all they had back then
http://www.makershed.com/product_p/jm1954834.htm
http://www.allelectronics.com/make-a-st ... ers/1.html

Wow---what a mess... Sorry it took out your speaker !

Have read that these are really good radios & see them on Ebay occasionally... Possibly other Zenith sets of that era & size
may have used same speaker---perhaps someone who has a good Photofact collection could look through parts
lists of a few to see...

Would definitely look into that FM RF transistor sub specs to see if it'll do the job !

Think I've seen a chassis # misprint on a Zenith label before---but not sure if it was one of mine...

And that battery leakage can cause "hidden" damage ! It can "seep" inside resistors around the leads & corrode internally & "wick" into wiring & do the same...

Let us know how it goes, even with a temporary external speaker !

John

...replacing the speaker should not be too big a problem; according to the manual, the original speaker is 2 3/4 inch AlNiCo with an impedance specified as '12 ohms at 400 cycles'...don't see why an 8 ohm wouldn't work...just didn't know if I'd be committing a 'sacrilege' by using a non-original speaker, but I guess that isn't a real problem here ...
...oh, yes, I'm aware of the kinds of insidious damage battery leakage can cause. I'm thoroughly expecting to find some weakened leads, etc. It already has solved the problem of replacing one of those Callins caps for me...the one at the bottom of my last picture (which didn't quite focus properly) that has yellow spaghetti on one lead. This cap goes to the earphone jack (it's the speaker coupling cap from the OTL output stage); the stuff wicked up the inside of the spaghetti and weakened that lead to the point that it broke off right at the end of the cap body, so I have to replace it, no matter what...it's a 50µF 6V; I'll replace it with a 47µF 16V (if I can find an axial-leaded one, so much the better)...the others are two 180µF 6V, a 12µF 15V, and a 10µF 6V. Again, I don't see a problem replacing the 180µFs with 220µF 16V (those are filtering caps on the main supply line, so they probably are not critical). The 12µF 15V is kind of a strange value; it's a bypass cap off the primary of the first FM IF transformer (actually, it's some extra filtering on the supply going into the FM front end); again, I'm not sure that that value is that critical, either, so I'm thinking I could probably get away with a 10µF 16V. The 10µF 6V is the electrolytic in the FM detector stage; a 10µF 16V will also go there. There are two other electrolytics that are not Callins; they're two Japanese 5µF 12V that I can use 4.7µF 16V to replace...the Callins electrolytics have something of a bad reputation, and at any rate, even in a transistor radio, I'm not going to trust 45+-year-old electrolytics...
...The original FM RF transistor was a 121-411, which the manual specifies as a 2N3588. I remember the SK3006 as a sub for many AM radio RF and IF transistors, but I don't remember if it was spec'ed to work at FM frequencies. The original 2N3588 is listed as an Amperex transistor and I'm going to say it was very likely of European origin (seems to me a lot of Amperex transistors came from either Germany or the Netherlands; it also has an unusual B-E-C basing that I believe was also chiefly found on European transistors)...



...right here in Brunswick, ME (see April Finds and Losses thread), 4 bucks...

2N3588 is subbed by the SK3006 and also ECG160(now NTE160) according to the Sams substitution book I have. I'd leave it alone if it works OK once you find a speaker. I too have the same radio and it is actually a good performer for what I call a "brick".

...update: I found a speaker on eBay that should work. It was an old (NOS) Motorola replacement speaker; it's the same 2 3/4 inch diameter. The magnet on it is slightly larger across than the original, so I had to do a little trimming on the battery tray (it has to fit inside a channel in the center of the tray). It may be a higher-impedance speaker (I realize that there is a difference between impedance and resistance, but the resistance of the voice coil measures considerably higher than that of a typical 8-ohm), but it does have continuity and it does work. I don't know how critical VC impedance is in an OTL output stage, but I doubt a higher impedance will damage it (perhaps the higher-impedance speaker might need a different coupling capacitor value than the original 50µF?)...at any rate, I now have a working speaker for it...
...and there appears to be one production change in this radio: I said one of the Callins electrolytics was a 12µF. That was what the schematic called for (C17), but the C17 in this radio turned out to be a 20µF 6V. Replacing it with a 22µF...also using higher voltage ratings than the original 6V (10 or 16V). The two non-Callins caps I wound up using 4.7µF 50V caps to replace...
...still more work to do. I'm removing most of the components that were in the vicinity of the battery tray (mostly resistors) so I can do a good cleanup of that part of the PCB; will probably end up replacing the resistors to be on the safe side (no telling what the battery leakage might have done to them). One resistor was severely discolored to the point I couldn't read its value (looks like the 15k off the AM detector that feeds the AGC line...one thing I don't get with this Zenith schematic is that very few of the resistors have reference designators...this particular resistor included)...

...yeah, I know...I'm putting a lot of work into this thing...but to me that's a lot of the fun of collecting these older radios...putting the work into them and making them work...not to mention it keeps my skills alive...

IDK if they even make Electrolytic caps with less than a 10 volt rating anymore, but regardless, the radio operates on four 1-1/2 volt cells, so any rating at or above 6 volts is adequate.

...I think there are still 6.3-volt-rated caps, as well as a few special-purpose caps with even lower ratings for use in 3.3V systems (such as motherboards). However, I believe in having a little 'fudge factor' with regards to working voltages, especially since it doesn't seem to be as critical with modern electrolytics as it used to (old school of thinking was to use a working voltage as close to the actual voltage as possible to keep the caps 'formed'), so I like to use higher voltages (16V seem to be especially common and give plenty of 'headroom' in this application)...

I have one that the speaker went out on. Worked fine one day and the next was silent.
According to the Samsfotofact that I have, the speaker is rated at 45 to 50ohms. Pretty darn hard to find.
Is the voice coil still good on the old speaker? If so what is the resistance?

Stan

...unfortunately, the voice coil in mine is open, as well as the cone being completely trashed. The particular version I have calls for a 12 ohm speaker, and the Zenith schematic actually gives a 12 ohm measurement. There are at least three different versions of this 9XT41 chassis that I know of: Royal 51 (-Z2), Royal 51-1 (-Z3) and Royal 810 (-Z8/Z9), and I think they all used different speaker impedances. It's an early form of the transformerless output stage, where you frequently encounter unusual speaker specs...but I'm not sure how much of a difference a few ohms of impedance would actually make...
...I'm nearing completion with mine; I completely stripped the PC board in order to clean off all the battery residue and wound up replacing a lot of parts (I had plenty lying around to work with), and have finished repopulating it (except for that SK3006...I'm going to put an NTE160 in its place as soon as I get it, which will require some tweaking of leads as the B and E leads are reversed)...some 'after' pictures will be forthcoming...

Looking at your pictures, looks like the PN is different on yours than mine. I have a 810, they look identical on the outside.
Mine was in almost perfect condition, except for being dirty and the dial was scratched up. I used some Novus and lots of elbow grease and it cleared up so well can't even tell it was scratched. How many ohms is the replacement?

...well...have everything back together. Repainted the front grille...

...used some Rust-Oleum metallic oil-rubbed bronze enamel. Does not match the original color (it's much darker, almost black), but definitely looks better (of course, I suspect the original finish was anodized anyway, and I wouldn't know the first thing about restoring that)...
...then got the PC board repopulated...

...including the new NTE160 in place of that SK3006. Much better fit, although I had to do some fancy lead bending and insulate the base lead (had to cross it over the emitter to reproduce that oddball B-E-C basing)...
...and got the battery box back in place...

(man, this dratted camera does not like to focus very well... )
...put four new AAs in it and turned it on. The speaker I found as a replacement seems to work reasonably well. Got activity on FM when I held onto the antenna wire (didn't mount the whip antenna yet), but nothing on AM. FM stations were off considerably, so figured an alignment will be in order, as well as troubleshooting the AM oscillator. Removed the batteries and set everything aside...but the next time I put the batteries back in to start to check things out, the FM no longer worked...so I have to troubleshoot BOTH oscillators... ...also had to open up the volume control and clean it out (it was noisy and simply spraying it with Deoxit wasn't helping, but a little on a Q-tip once I had the control apart did)...

The grille looks pretty good and its a nice match. Well done!
I'll have to agree it would be nearly impossible to duplicate that anodize finish otherwise.

Just a tip... increasing the light levels in the room will make closeup focusing easier.

~ Mitch ~

As will moving back. I think that most if not all of these are too close-up, shorter than the close-focusing distance.

Brett

No need to move back, just make sure the camera is in macro or super macro mode.
I'm sure you've seen some of the pics I've posted with my el-cheapo HP camera, right?
Remember, nearly every digital camera made in the past several years has a closeup feature.
All will produce great images with the proper settings and good lighting. Brighter light
levels also increase the chance of getting a better image because of the shorter exposure
time. Helps when the camera is gets shaky.

~ Mitch ~

...think I've found my oscillator problem. The oscillators are probably working; I just can't tune them. The tuning capacitor is one of those Japanese 'polyvaricons' (four-section Mitsumi PVC-2FX; there were probably zillions of them out there at one time...virtually every Panasonic AM-FM radio made in those days used some variant of it...and Lord knows how many other manufacturers as well...); it's all loosened up and the rotor plates don't move when you turn the shaft. And that's probably my own fault: I think I probably contaminated the dratted thing with rosin during my disassembly work and gummed it up, so when I tried to turn the thing, it wound up loosening the shaft (the things are held together with nuts, and the shaft and rotor plates are not slotted or keyed; the whole thing depends on the nut on the inner end of the shaft being very tight. If the nut is loose, the shaft will just turn freely inside the plates and the plates won't move). Also wound up breaking the stops so the shaft turns more than the normal 180 degrees. Not having one of these with an actual shaft, I am about to do the insane: try to clean and rebuild it. I have removed and separated the four separate sets of plates for cleaning and decontamination, but will first try to repair the broken stops...
...need to get me some alcohol to decontaminate the plates (I don't think alcohol will harm the polyethylene sheets)...

...well...that didn't work. I need to find a donor radio for another tuning cap (as previously mentioned, virtually any smaller Panasonic AM-FM radio from the late 60s or 70s would provide one). After taking great care to separate out the four sections of the cap, and repairing the broken stops, turns out the base of the cap had cracked right through the middle and it broke right in half...tried super-gluing it but it didn't hold...
...now, these caps usually had that very short double-flatted shaft with the threaded hole in the middle for directly attaching a thumbwheel tuning knob or a drum. Finding one with an actual 1/4-inch diameter shaft like this one had is probably going to be next to impossible. So what will probably wind up happening is I end up finding a suitable replacement tuning cap, but will still have to perform an operation to change shafts...I have saved the parts from the original cap for just such a contingency...

Thought about it the other day & pretty sure I remember seeing a brass adapter on a radio which was designed
to fit on those polyvaricon double-flatted shafts---had two machined tabs which tightly straddled the cap shaft
and had a screw which went down a center hole to secure it... Been a long while ago, but maybe this will spark the
memory of someone who might still have a junk set or PCB that uses one...

John