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 Post subject: Zenith Royal 73 project...
PostPosted: Feb Fri 09, 2018 4:15 am 
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Joined: Oct Mon 26, 2009 10:02 pm
Posts: 5736
Location: Indianapolis, IN
Couldn't pass this radio up for what it cost (Buy It Now) and after arrival today, am glad I got it---worked excellent right out of the box and is in very good shape other than the hinge area & snaps of back cover and a bunch of tiny paint spots.

Think this might be Zenith's last AM-only portable set with tuned-RF amp stage---anyone know for certain ??? It shares the same chassis as the earlier Royal 68 in collection and is made in Hong Kong...

More to come... Ebay pic below

John


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arf r73 ebay pic.jpg
arf r73 ebay pic.jpg [ 235.31 KiB | Viewed 898 times ]
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 Post subject: Re: Zenith Royal 73 project...
PostPosted: Feb Sun 11, 2018 4:57 pm 
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Joined: Jan Tue 31, 2012 1:55 am
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Location: Mountains of Mourne. Ireland.
Image
Image
Sams TSM 106 November 1969
Zenith R73J, R73L, Royal 73J and Royal 73L chassis-9YT57Z9

If I'm not mistaken, Zenith Royal 68 employed chassis-9XT56Z9

Greg.


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 Post subject: Re: Zenith Royal 73 project...
PostPosted: Feb Sun 11, 2018 5:24 pm 
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Joined: Oct Mon 26, 2009 10:02 pm
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Location: Indianapolis, IN
Hey Greg---you found the same brochure that I did the other day, thanks for posting !

Am almost certain I saw the factory Zenith service info that covered both both models and that they were electrically identical---maybe some slight mechanical differences due to somewhat different control panel ? I looked in my Royal 68 folder thinking I had it, but didn't---so looked online for image and found front page. You are correct about the chassis number differences, but at a glance they do look identical...

John


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arf 68 73 factory front page.jpg
arf 68 73 factory front page.jpg [ 147.09 KiB | Viewed 837 times ]
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 Post subject: Re: Zenith Royal 73 project...
PostPosted: Feb Mon 12, 2018 3:43 am 
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Joined: Oct Mon 26, 2009 10:02 pm
Posts: 5736
Location: Indianapolis, IN
Spent the day completing this radio...

It required hours to pick off & remove paint specks and "dry clean" the dust in grille slots with toothbrush and vacuum cleaner since panel couldn't be removed from radio (appeared to be glued at top edge). Scrubbed surface of chrome with old cotton sock dampened with Windex. The trim-plate behind volume & tone controls was loose, so removed, cleaned, and re-glued. The tuning side trim-plate lettering and edge paint started to come off, so carefully cleaned with water dampened cloth---but even water started to remove the black stripe around top and right side edges (argghhh !)... Used compressed air to blow dust off of PCB and cabinet...

The radio was already an excellent performer with very good sound, but "tweaking" still made a noticeable improvement.

Few project pics below with the last showing the Royal 68 & Royal 73 together. Basically the same radio with different cabinet styles...

Still curious if this set is the last AM-only Zenith portable with a tuned-RF amp stage---anybody know ?

John


Attachments:
ARF R73 PCB BOT.jpg
ARF R73 PCB BOT.jpg [ 227.13 KiB | Viewed 820 times ]
ARF R73 CAB INS CLN.jpg
ARF R73 CAB INS CLN.jpg [ 239.18 KiB | Viewed 820 times ]
ARF R73 INS CLN.jpg
ARF R73 INS CLN.jpg [ 242.22 KiB | Viewed 820 times ]
ARF R73 CVR INS CLN.jpg
ARF R73 CVR INS CLN.jpg [ 216.64 KiB | Viewed 820 times ]
ARF R73 CMPLT.jpg
ARF R73 CMPLT.jpg [ 204.17 KiB | Viewed 820 times ]
ARF R68 R73.jpg
ARF R68 R73.jpg [ 186.52 KiB | Viewed 820 times ]
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 Post subject: Re: Zenith Royal 73 project...
PostPosted: Feb Wed 14, 2018 3:54 am 
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Joined: Mar Sun 30, 2008 1:45 am
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Location: Oakland Township, Michigan
Sharp looking! When were those radios produced John?

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 Post subject: Re: Zenith Royal 73 project...
PostPosted: Feb Thu 15, 2018 2:29 am 
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Joined: Oct Mon 26, 2009 10:02 pm
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Location: Indianapolis, IN
Thanks Matt---Not certain, but think the Royal 68 came out in late '67 and the Royal 73 in '68 from what date-codes and advertising I could find. If anyone knows for sure, please post !

John


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 Post subject: Re: Zenith Royal 73 project...
PostPosted: Mar Mon 18, 2019 2:18 pm 
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Location: Burke, VA
I think there was another AM-only portable with a TRF stage following this one. It's the Royal E71, a few examples of which I've seen so far are labeled with model number RE-71J. Don't know when the E71 was manufactured but its service manual was dated August 1973. Without the fixed handle, it shares the same appearance as the Royal 68. It was designed for battery or AC operation. It has no transformers in the audio stages, similar to the redesigned Royal 73-2. There is a doubled-tuned IF transformer following the mixer stage which should give the E71 better selectivity than both the 68 and 73.


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1arf_Zenith_Royal_E71_Front.jpg
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2arf_Zenith_Royal_E71_Bottom.jpg
2arf_Zenith_Royal_E71_Bottom.jpg [ 130.14 KiB | Viewed 158 times ]
3arf_Zenith_Royal_E71_Part_Map.jpg
3arf_Zenith_Royal_E71_Part_Map.jpg [ 187.58 KiB | Viewed 158 times ]

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 Post subject: Re: Zenith Royal 73 project...
PostPosted: Mar Mon 18, 2019 3:28 pm 
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Location: Indianapolis, IN
Hello Binh,

Thanks for the info & pics ! Am not familiar with that set, but am curious about the circuit---especially the Q501 "stabilizer" transistor (which may just be for audio output bias regulation ?)...

John


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 Post subject: Re: Zenith Royal 73 project...
PostPosted: Mar Mon 18, 2019 3:38 pm 
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Joined: Jun Sun 22, 2008 2:03 am
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Location: Burke, VA
Hi John,

The Q501's function may be what you guessed. Will know what it does when the radio arrives in a few days. Got both of these this weekend and will have a chance to compare them.

Edit:
From what could be made out from the tiny and fuzzy schematic at RM, it looks like Q501 is used as a supply voltage regulator for the RF and IF transistors (will have to wait 30 days before full size could be downloaded).


Attachments:
4arf_Zenith_Royal_E71_Fuzzy Sch.jpg
4arf_Zenith_Royal_E71_Fuzzy Sch.jpg [ 60.07 KiB | Viewed 122 times ]

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 Post subject: Re: Zenith Royal 73 project...
PostPosted: Mar Mon 18, 2019 5:11 pm 
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Joined: Oct Mon 26, 2009 10:02 pm
Posts: 5736
Location: Indianapolis, IN
Hello Binh,

Very interesting that they used a special voltage regulator for the RF/IF circuits ! EDIT: Just saw your "fuzzy" schematic and realized that set has a built-in power supply for AC operation which would explain why they might want regulation---and it would "stabilize" front-end when battery voltage dropped if Zener below normal input voltage ?

Please remember to report comparison results when you have the radios...

Thanks !
John


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 Post subject: Re: Zenith Royal 73 project...
PostPosted: Mar Mon 18, 2019 5:30 pm 
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Joined: Jun Sun 22, 2008 2:03 am
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Location: Burke, VA
It does indeed "stabilizes" the front end circuits, especially the frequency of the Osc circuit. Also any capacitance across the Zener diode (intrinsic or external) is multiplied by beta of Q501 (e.g. 1 uF will become 100uF for a beta of 100). This helps to clean out the noise in front-end supply rail.

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 Post subject: Re: Zenith Royal 73 project...
PostPosted: Mar Tue 19, 2019 2:56 pm 
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Location: Mesquite NV 89027 (from Coventry, UK)
That’s a sharp looking radio.


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