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 Post subject: 2nd Zenith Royal 490 project--those "irresistable orphans" !
PostPosted: Feb Fri 23, 2018 3:06 am 
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Joined: Oct Mon 26, 2009 10:02 pm
Posts: 5466
Location: Indianapolis, IN
Hello All,

Saw this poor, somewhat ragged "orphan" on Ebay for awhile and when I saw the minimum bid drop to $8 with free shipping on the latest re-listing, placed mine at last moment and won it with no competition... Already have one in collection and it's a great performing/sounding radio... Was pretty excited to find that this one wasn't as bad as I thought once unpacked... It evidently belonged to someone named "Dee" as it is clearly printed on edge of back cover inside...

This is the set in which Zenith upgraded the very good, tuned-RF amp stage equipped Royal 475 design with a longer ferrite antenna, OTL audio output, and lowered the supply voltage to 6V---creating an outstanding performer with excellent sound quality. The same basic chassis was carried forward to the Royal 705/66 sets with the three audio transistors being changed from NPN to PNP...

The cheap "Perma-wear" cabinets didn't hold up very well on these, but the styling was neat. The front of this one isn't too bad, though, compared to some... The inside has some rust/corrosion on chassis, tuning cap, and a few components on bottom edge of PCB---but the battery contacts are in very good shape and compartment cleaned up well. The tuning seemed to be binding badly, but fortunately it turned out that the dial had come loose from backing and was jammed against knob---pulled knob out slightly and it now tunes smoothly from end to end...

Saw that the chassis was only fastened with one of the four screws when I removed it. After cleaning battery compartment, installed batteries and turned on---absolutely nothing... After checking supply voltages past switch, began troubleshooting from speaker back and found that the audio driver transistor had been cut out by someone ! Surprised this wasn't noticed at first inspection... Used test-leads to temporarily attach a replacement and was able to receive a strong local at very low volume---will replace electrolytics before proceeding further...

A couple Ebay pics below... EDIT: Added one of the inside of back cover...

Stay tuned !

John


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ARF 490 EBAY PIC3.jpg
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ARF 490 EBAY PIC1.jpg
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arf 490 back cover ebay pic.jpg
arf 490 back cover ebay pic.jpg [ 171.69 KiB | Viewed 491 times ]


Last edited by xrhonda91 on Feb Sun 25, 2018 2:03 am, edited 1 time in total.
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 Post subject: Re: 2nd Zenith Royal 490 project--those "irresistable orphan
PostPosted: Feb Fri 23, 2018 3:42 am 
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Joined: Nov Wed 14, 2007 11:37 pm
Posts: 1475
Wow, you got a good deal on that one! For some reason I like battleworn sets. Especially when they're brought back up to high performance. Hey, that antenna looks real familiar!


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 Post subject: Re: 2nd Zenith Royal 490 project--those "irresistable orphan
PostPosted: Feb Sat 24, 2018 6:12 am 
Member

Joined: Oct Mon 26, 2009 10:02 pm
Posts: 5466
Location: Indianapolis, IN
Hey Metzman---always good to take an unwanted, somewhat rough "orphan" and to make it clean, presentable, and functional (if it was known to be a good performer in a previous "life")... Yep---this has the earlier version of the chassis used in the Royal 705/66 sets, so imagine the antenna is the same or very close...

Progress this evening !

Replaced all the electrolytics and installed a transistor socket for audio driver. Installed a Sylvania NPN audio transistor and batteries for testing. When turned on, basically the same thing as yesterday---only more stations came in at very low volume and they were now distorted. Adjusting the volume control made no difference as before, so checked resistance at both ends to wiper and across element and all fine---resistance also varied smoothly when shaft rotated. Hmmm... Using another radio as an amp for audio tracing, probed back to the detector output circuit with same low, distorted result. When probed at detector diode cathode connection to 3rd IFT output, signal very strong and discovered that diode was open ! Could see that leads at both anode and cathode had been corroded somewhat by whatever had gotten into radio, but not sure if this caused failure. Had both NOS Germanium and new BAT-46 diodes, so tried one of each without noticing any great difference in performance---the BAT-46 seemed to give just a tiny bit more "clarity" to audio, so installed it. Radio now performs great and sounds as it should (thankfully, the volume ctl./switch is fine !) without making any adjustments whatsoever, but will "tweak" during daytime tomorrow before installation into cabinet (which still needs detail cleaned)---and
Pics of original caps, defective detector diode, and tuning dial sections before re-gluing below...

More tomorrow !

John


Attachments:
ARF 490 orig caps-corroded det diode.jpg
ARF 490 orig caps-corroded det diode.jpg [ 214.74 KiB | Viewed 538 times ]
ARF 490 tuning dial sections.jpg
ARF 490 tuning dial sections.jpg [ 218.73 KiB | Viewed 538 times ]
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 Post subject: Re: 2nd Zenith Royal 490 project--those "irresistable orphan
PostPosted: Feb Sat 24, 2018 9:13 pm 
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Joined: Oct Mon 02, 2017 8:53 am
Posts: 56
That's the first 2uf cap I've seen in any Zenith.


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 Post subject: Re: 2nd Zenith Royal 490 project--those "irresistable orphan
PostPosted: Feb Sun 25, 2018 1:56 am 
Member

Joined: Oct Mon 26, 2009 10:02 pm
Posts: 5466
Location: Indianapolis, IN
Zenith Royal---that's a good reason to get the radio it's used in !

Got it done today !

Have only a small quantity of spare germanium NPN transistors, so as mentioned earlier, first tried an old NOS Sylvania oval which I've had for many years for the missing audio driver. For some reason, these transistors didn't have a "findable" part number---maybe some transistors Delco was evaluating back in the '50's that were given to me as a kid by Dad or another older engineer friend ??? It seemed to work great... I've also used one or two in other sets with good results in same application. Since I really wanted to save the couple I have left for "special" radio repairs, thought I'd also try a silicon 2N4124 and it did work, but with less volume and sound quality---so went back to the Sylvania part...

The trimmer screws on tuning cap were also corroded, so removed and cleaned with stainless-steel "toothbrush" and Windex, rinsing with water... There was also some slight oxidation on the aluminum plates, so folded a piece of paper to fit snugly between and cleaned.

Once chassis back together and blew out gently with compressed air, installed batteries and turned on---with just a bit of tweaking of the ANT & RF trimmer, performance now outstanding ! Amazingly, the IFT's seemed to be fine as they were...

Spent hours carefully cleaning the case, using damp Q-tips very gently around the speaker "grille" and stitching to avoid damage. The small area in upper center of front that appeared to be scratched turned out to be a "strand" of some type of sticky adhesive which fortunately came off well with fingernail and very careful use of Isopropyl alcohol on Q-tip avoiding contact with lettering. The handle brackets are badly rusted, so just cleaned as well as possible---the corrosion on inside has actually "seized" the ends of handle, so it is stuck in the "down" position and would be too risky to attempt removal...

Installed chassis into clean cabinet using four slotted 6-32 screws of proper length with integral lockwasher since three of the original hex-head screws were missing. Pressed knobs into place...

Have you ever gotten "chills" when a radio performed & sounded better than expected when complete and first turned on ? Held the completed radio in hand and turned on---WOW ! Not only was the performance across entire band outstanding, but with chassis in cabinet so was the sound ! Noticeably more clear audio "punch" than the other 490 and the 705/66's---maybe the new Sylvania driver transistor ??? You could feel the radio "vibrate" when volume turned up and sound quality still good !

Very grateful for how good this well-used "gem of an orphan" cleaned up and works ! Actually looks better from the front that my other 490...

Project pics below with last two showing this set with the other 490 & one of the "pretty" Royal 705's...

John


Attachments:
ARF 490 PRTS OUT CLEAN.jpg
ARF 490 PRTS OUT CLEAN.jpg [ 177.79 KiB | Viewed 492 times ]
ARF 490 PRTS IN CLEAN.jpg
ARF 490 PRTS IN CLEAN.jpg [ 153.31 KiB | Viewed 492 times ]
ARF 490 CAB INS CLEAN.jpg
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ARF 490 CAB FRT CLEAN.jpg
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ARF 490 TRIMMER SCREWS CLEANED.jpg
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ARF 490 CHASSIS CMPLT FRT.jpg
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ARF 490 CMPLT INS.jpg
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ARF 490 CMPLT FRT.jpg
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ARF 490 PAIR.jpg
ARF 490 PAIR.jpg [ 125.47 KiB | Viewed 492 times ]
ARF 490 705.jpg
ARF 490 705.jpg [ 124.55 KiB | Viewed 492 times ]
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 Post subject: Re: 2nd Zenith Royal 490 project--those "irresistable orphan
PostPosted: Feb Sun 25, 2018 3:17 am 
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Joined: Nov Wed 14, 2007 11:37 pm
Posts: 1475
Superb work! Looks like your handle is actually in pretty good shape with no cracks in the middle . Interesting how they added a bezel to the volume knob. I wonder how zenith came up with their numbers. Like how did they get"66" from " 705". And where did 705come from. There sure are a lot of them in the royal line.


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 Post subject: Re: 2nd Zenith Royal 490 project--those "irresistable orphan
PostPosted: Feb Sun 25, 2018 5:19 am 
Member

Joined: Oct Mon 26, 2009 10:02 pm
Posts: 5466
Location: Indianapolis, IN
Thanks much, Metzman !

That bezel is kind of a neat styling touch to "balance out" the control panel---one of the things I like about its appearance...

I would also like to know how they came up with their model numbers ! They went from 3 to 2 digits on all their Royal sets around 1965-66 (I believe)---500 to 41, 555 to 56, 755 to 74, 790 to 97, 705 to 66...

That is one of the "purty" 705's to show off on shelf---the one in family room has a handle which is only held together in center by the thread !

Have been listening to Zoomer 740 on this 490 all evening---the sound is just fantastic for an older set of its size (even though the 490 and 705/66's do sound great "stock") . I left the socket inside for the driver transistor in case I ever find an original part---would sure be interesting to see if it's just that Sylvania transistor itself giving the audio so much more "oomph" on this radio ! Guess I could just disassemble the other one and experiment, but really don't want to take apart and de-solder a good transistor from a working radio just to "play"...

And forgot to mention that Zenith began to use Japanese parts in the 705---the transistors & IF transformers are obvious differences... Would be glad to hear from anyone who has Zenith production info...

John


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 Post subject: Re: 2nd Zenith Royal 490 project--those "irresistable orphan
PostPosted: Feb Sun 25, 2018 6:57 pm 
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Joined: Aug Wed 26, 2009 1:50 am
Posts: 1406
Location: Mount Pleasant UT 84647 (from Coventry, UK)
That cleaned up well. Great work as always!


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 Post subject: Re: 2nd Zenith Royal 490 project--those "irresistable orphan
PostPosted: Feb Mon 26, 2018 4:06 am 
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Joined: Oct Mon 26, 2009 10:02 pm
Posts: 5466
Location: Indianapolis, IN
Thanks Colin---A bit of a challenge, but well worth the effort !

John


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 Post subject: Re: 2nd Zenith Royal 490 project--those "irresistable orphan
PostPosted: Feb Mon 26, 2018 6:39 pm 
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Joined: Oct Mon 26, 2009 10:02 pm
Posts: 5466
Location: Indianapolis, IN
Okay Guys---gotta correct myself on the performance of this set (embarrassing)...

Was pretty excited on how well it worked after repairs, especially the extra "audio punch" which may be due to the Sylvania transistor used to replace audio driver, but when comparing it to the Royal 705 this morning during "day-off work playtime" found that it's just not as sensitive/selective during a side by side test.

Initially tried to find the same weaker DX stations discovered on the Philco T805 and a couple couldn't even be heard and another which was adjacent to stronger signal had interference. Grabbed the Royal 705 from family room table and found that it did much better, but still fell behind the Philco a bit.

Tried "tweaking" trimmers with chassis in cabinet with paper-clip "tool", but they were still fine as were the IFT's. Pulled the other 490 off shelf and found that it is also not quite as "hot" as the 705 and the lower end of dial is noticeably "weaker" than this set (and as expected, the audio doesn't have that extra "oomph" with original driver)... Anyone else have both a 490 and 705/66 to compare ???

Sorry...

John


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