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 Post subject: Zenith Royal 755G - spare cabinet & chassis mating project
PostPosted: May Fri 20, 2022 11:09 pm 
Member

Joined: Oct Mon 26, 2009 10:02 pm
Posts: 7514
Location: Indianapolis, IN
Hello All,

Over eleven years ago, I bought my first Zenith Royal 755G to refurbish. Turned out to be an excellent radio. Major issue was that battery leakage had eaten away the lower right corner of leather cabinet and damaged the left. An ARF friend sent me a spare cabinet from a junked set for cost of postage, but the leather, though good looking, was a bit dry and stiff while the damaged original was still soft and pliable and had that good leather aroma. So decided to keep original cabinet and wrapped the donated replacement and placed in radio closet thinking someday I might find a good chassis for it. Then a couple years ago, saw another member list a complete chassis in classifieds and kept an eye on it still not sure if I wanted to build another another since I also needed a tuning knob and didn't want to spend a lot of money on project. The chassis never sold and recently thought I'd ask if he still had it---he did and basically gave it to me for cost of shipping which was much appreciated. Chassis arrived fine and appeared to be in good, all original condition.

Applied power with clip leads and heard nothing but slight hiss at full volume. Did a bit of detail cleaning and replaced all factory electrolytics. After electrolytics replaced, did barely hear a distorted strong local at maximum volume. Did a bit of tracing and discovered that no noticeable signal was coming from detector circuit. Checked resistance of 3rd IFT secondary and it was open ! Removed and disassembled can and found that one of the wires was broken internally at terminal. There was also a small "chunk" of broken ferrite material inside and it wasn't from this part---kind of an odd production error. Thankfully, there was enough of a lead left from coil that I was able to reattach it. Verified all else okay and reassembled---radio now worked and sounded great ! After alignment, it was an excellent performer with very good sound as these typically are.

The spare leather cabinet did need a good detail-cleaning, so carefully went over it with water-dampened, then dry soft cotton rag pieces avoiding the old stitching. Was able to remove paint specks with careful use of fingernails. Turned out very well. One of the back cover snaps came off due to minor battery leakage damage, but overall in nice shape. The cover hinge area is very stiff, so it definitely needs some leather conditioner before it cracks ! The dense black foam rubber speaker gasket was improperly positioned , so had to carefully remove it, clean old adhesive residue from interior cabinet surface, and reinstall. To maintain proper form of gasket. traced cabinet speaker opening on piece of cardboard matting and cut to shape---this did the job, but I overlooked the fact that I needed to see where to position gasket while gluing into place ! So traced the opening again on a piece of sturdy thin plastic from parts container and cut it to shape---this did the trick and not only held gasket into proper form, but could easily see where it needed to be positioned for gluing. To hold gasket firmly in place while glue cured, cut the "peak" off one of my old transparent "Peak Performance" awards from Northrop Grumman with Sawzall so it would fit inside cabinet since I needed to be able to see that gasket didn't shift while weighting it down. Once this was in place, added heavy old steel disk-drive actuator core for good measure while it sat overnight.

The chrome front panel also needed a good detail-cleaning. The tuning dial window had some scratches and scuffs that required careful wet-sanding with 2000-grit and multiple passes of polishing with Novus-2. Thankfully, it also turned out well.

Unfortunately, didn't have the original pal-nuts to attach panel to cabinet and looked all over to find some---even asked here and another FB radio site. Had a drawer of them from my automotive project days, but the 1/8" (which I found were the smallest available) were slightly too large for the 3/32" tapered chromed studs. Didn't want to gamble buying any others and paying shipping for something that wouldn't work, so decided to try and "modify" six of the ones I had. Used a flat punch and hammer with anvil to flatten the "domed" head and hopefully reduce the I.D. of thread-cutting hole and this gratefully worked ! It took a bit of force with nut-driver having panel flat on bench to engage and tighten them, but all six finally cooperated and it is now securely attached to cabinet. Just as an added measure, applied a small "glob" of Loctite Extreme glue around stud on top of each nut. Will leave this to cure overnight before further handling...

Still don't have a tuning knob, so if I can't find one (cheap), will attempt to make an insert for a spare volume knob to fit the small "D"-shaft of tuning cap.

Getting there !

Project pics thus far below---please "click" on images for larger view !

John


Attachments:
001ARF 755G CHS CMPLT FRT 5-20-22.jpg
001ARF 755G CHS CMPLT FRT 5-20-22.jpg [ 805.76 KiB | Viewed 487 times ]
002ARF 755G CHS CMPLT BK 5-20-22.jpg
002ARF 755G CHS CMPLT BK 5-20-22.jpg [ 669.87 KiB | Viewed 487 times ]
01ARF 755G CAB SPKR GSKT POS FIX TOOLS 5-20-22.jpg
01ARF 755G CAB SPKR GSKT POS FIX TOOLS 5-20-22.jpg [ 744.19 KiB | Viewed 487 times ]
02ARF 755G CAB SPKR GSKT POS FIX 5-20-22.jpg
02ARF 755G CAB SPKR GSKT POS FIX 5-20-22.jpg [ 716.86 KiB | Viewed 487 times ]
03ARF 755G CAB SPKR GSKT POS CORRECTED 5-20-22.jpg
03ARF 755G CAB SPKR GSKT POS CORRECTED 5-20-22.jpg [ 658.39 KiB | Viewed 487 times ]
04ARF 755G CAB PRTS CLN & READY 5-20-22.jpg
04ARF 755G CAB PRTS CLN & READY 5-20-22.jpg [ 798.27 KiB | Viewed 487 times ]
05ARF 755G REWORKD PALNUTS 5-20-22.jpg
05ARF 755G REWORKD PALNUTS 5-20-22.jpg [ 398.17 KiB | Viewed 487 times ]
06ARF 755G CAB FRT PNL MNTD 5-20-22.jpg
06ARF 755G CAB FRT PNL MNTD 5-20-22.jpg [ 720.6 KiB | Viewed 487 times ]
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 Post subject: Re: Zenith Royal 755G - spare cabinet & chassis mating proje
PostPosted: May Sun 22, 2022 1:05 am 
Member

Joined: Oct Mon 26, 2009 10:02 pm
Posts: 7514
Location: Indianapolis, IN
Completed this project today !

Since I only had two volume knobs in spare parts stash, decided to attempt to modify one to be used for tuning. Examined both a volume knob and a good tuning knob from another radio and it appeared that I could simply make an insert that would fit the very small tuning shaft. Thought of what would make a good material and decided on pieces of sturdy but flexible clear plastic salvaged from commercial parts packaging. It looked as though two layers would give needed thickness, so cut strips as wide as knob shaft opening was deep. Formed a "flat" with miniature needle-nose pliers and formed curve to match outside of volume shaft. Held next to opening and cut off excess to get a snug fit. Pressed piece in and "worked" it into cavity. Repeated this process for the smaller second insert. Carefully worked modified knob onto the tuning shaft and it fit perfectly---good and snug with no "wobble" ! Since the plastic shaft on volume control knob was longer than tuning causing it to protrude further from front panel, marked and sanded it down to proper length with new inserts in place. Turned out great ! Now all I need to do is attempt to make a new bright since it is missing on this knob...

Spliced-in a new 9V-battery style connector and performed a precise alignment before installing chassis. Went through hardware drawer and found four screws of proper threading and length to attach it to front panel. Works great and looks much better than 1st 755G from many years ago !

But---after tuning around a bit, the vernier drive started to slip for some reason. Arghhh ! Pulled chassis and discovered that the tuning cap had become very tight. Disconnected dial-cord and same thing. No idea what happened, but noticed that the center bushing on rotor shaft appeared corroded. Decided to oil it and the end bearing. The reduction bearings at front were dry, but I've seen that before in other Zenith sets and learned the hard way not to add lube there as it will begin slipping ! Applied small drops of synthetic oil and rotated pulley back and forth repeatedly---then added more oil. When it began to run off, carefully wiped off excess with paper towel. After doing this awhile, rotation became more smooth and easy, so after a final clean-up, reattached dial-cord and readjusted pointer alignment. All seemed fine, so reassembled and played with radio a bit...

Cut a piece of very thin aluminum from a scrapped 3-1/2" floppy-disk door and hope to attempt to make a bright for tuning knob when motivation strikes... Also need to get and apply a small amount of leather conditioner to rear cover hinge area---it is still intact, but very dry and stiff...

Project pics below---please "click" on images for larger views !

John


Attachments:
ARF 755G TUN KNB FRM VOL KNB 5-21-22.jpg
ARF 755G TUN KNB FRM VOL KNB 5-21-22.jpg [ 531.35 KiB | Viewed 425 times ]
ARF 755G  VOL & MOD 4 TUN KNB 5-21-22.jpg
ARF 755G VOL & MOD 4 TUN KNB 5-21-22.jpg [ 562.43 KiB | Viewed 425 times ]
ARF 755G  CMPLT XCPT TUN KNB BRITE 5-21-22.jpg
ARF 755G CMPLT XCPT TUN KNB BRITE 5-21-22.jpg [ 939.35 KiB | Viewed 425 times ]
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 Post subject: Re: Zenith Royal 755G - spare cabinet & chassis mating proje
PostPosted: May Sun 22, 2022 2:19 am 
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Joined: Feb Mon 21, 2011 4:19 pm
Posts: 555
Location: San Marcos, CA 92069
Congratulations John on another great restoration! The radio looks fantastic. I'm always impressed with your thoroughness and care in your projects. I've always thought the Royal 755 series is one of Zeniths best sounding AM transistor radios.

I am curious to see how your knob bright replacement turns out. I've a Motorola 53H radio with a missing knob bright. Unfortunately the bright is not flat, but is a slightly cone shaped circle. I'm using a flat bright, as my attempts to match the cone shape haven't looked very pretty.

Your knob insert is a great idea! I'm glad it is working out so well. Coming up with a plastic hard enough to withstand the torque when tuning, yet flexible enough to form into an insert seems like a lucky find. I'd have been tempted to try using soft copper from 1/4 inch tubing to form the insert.

Nash


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 Post subject: Re: Zenith Royal 755G - spare cabinet & chassis mating proje
PostPosted: May Sun 22, 2022 6:18 am 
Member

Joined: Oct Mon 26, 2009 10:02 pm
Posts: 7514
Location: Indianapolis, IN
Thanks Nash !

That clear plastic comes from that common, fairly heavy gauge material used to contain and display parts and other items in stores. Very tough, but flexible. Have used it for many projects including insulators, cleaning tools (basically cut end of a strip at an angle to get a point), and even the tuning pointer support in that Kobe Kogyo radio awhile back. You've probably thrown a bunch of it away through the years !

John


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 Post subject: Re: Zenith Royal 755G - spare cabinet & chassis mating proje
PostPosted: May Tue 24, 2022 7:44 pm 
Member

Joined: Oct Mon 26, 2009 10:02 pm
Posts: 7514
Location: Indianapolis, IN
Well---couldn't find anything to cut the very thin aluminum without distorting edge somewhat, so couldn't make the bright and decided to "cheat". The tuning knob on my 1st 755G has black (instead of white) base plastic where chrome wore off outside edge, but had a good bright that was a bit loose on one edge. Carefully ran fingernail around from that loose spot and then a strip of thin sturdy plastic to remove it. Cleaned off all old adhesive, waxed front surface, and glued it onto this set's tuning knob. Now set looks complete (picture below) and will take the place of 1st in display cabinet ! Hoping I can eventually find tuning (or volume knob to modify) which still has good chrome like the one on 1st set so those will match...

John


Attachments:
ARF 755G 2ND CMPLT 5-24-22.jpg
ARF 755G 2ND CMPLT 5-24-22.jpg [ 972.98 KiB | Viewed 313 times ]
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 Post subject: Re: Zenith Royal 755G - spare cabinet & chassis mating proje
PostPosted: May Tue 24, 2022 8:51 pm 
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Joined: Apr Thu 27, 2017 7:49 pm
Posts: 34
Location: Menlo Park, CA 94025
John, nice restoration, along with comprehensive details. I always find your tips useful, had never thought of the plastic wrap as a knob stabilizer and fit piece.

Bob


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 Post subject: Re: Zenith Royal 755G - spare cabinet & chassis mating proje
PostPosted: May Wed 25, 2022 2:27 am 
Member

Joined: Oct Mon 26, 2009 10:02 pm
Posts: 7514
Location: Indianapolis, IN
Bob---was thankful the plastic was of proper thickness to work as well as it did. That stuff is very tough and should be a permanent solution. Glad I saved it !

John


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