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 Post subject: Zenith RB-77T Automatic Station Seeking radio project...
PostPosted: Jul Thu 19, 2018 2:54 am 
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Joined: Oct Mon 26, 2009 10:02 pm
Posts: 5735
Location: Indianapolis, IN
Hello All,

Just received this radio today---seems to work well except FM seeking (FM works fine, seek doesn't stop)... Thanks to Bob for scanning 18 pages of service data !

Antenna broken off, but otherwise appears good but somewhat dirty...

Pics when time allows---stay tuned !

Anyone else have one of these ?

John


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 Post subject: Re: Zenith RB-77T Automatic Station Seeking radio project...
PostPosted: Jul Fri 20, 2018 2:47 am 
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Joined: Oct Mon 26, 2009 10:02 pm
Posts: 5735
Location: Indianapolis, IN
This is an excellent performer as it is !

Played with it tonight after preliminary clean-up and other than the seek circuit failure on FM, all else great along with the sound quality and volume (which will almost knock you back in chair when turned up !).

Was very impressed with the "seek" on AM---it would stop at every listenable signal including my favorite low-power DX station which was just above noise level after dark ! You have to be fast pressing the "rocker", but it would capture weak signals fine adjacent to more powerful ones...

Really neat radio, but am wondering about the 1968 date mentioned at RadioMuseum---the SAMS is dated '71 and styling looks much more like early '70's. If anyone runs across an ad on-line, please let me know...

More to come as time allows.

Below is an Ebay pic...

John


Attachments:
arf 77 ebay pic.jpg
arf 77 ebay pic.jpg [ 211.75 KiB | Viewed 1207 times ]
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 Post subject: Re: Zenith RB-77T Automatic Station Seeking radio project...
PostPosted: Jul Fri 20, 2018 3:03 pm 
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Joined: Feb Tue 10, 2009 3:16 pm
Posts: 745
Location: zipcode 46235
From what I've seen, the Photofact is issued roughly a year and a half after the radio is on the market. So, the Zenith was probably issued about 1969.


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 Post subject: Re: Zenith RB-77T Automatic Station Seeking radio project...
PostPosted: Jul Sat 21, 2018 3:48 am 
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Joined: Oct Mon 26, 2009 10:02 pm
Posts: 5735
Location: Indianapolis, IN
Thanks for the info, Battery-maker---will see what date codes might be inside !

John


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 Post subject: Re: Zenith RB-77T Automatic Station Seeking radio project...
PostPosted: Jul Sun 22, 2018 4:12 am 
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Joined: Oct Mon 26, 2009 10:02 pm
Posts: 5735
Location: Indianapolis, IN
Listening to Zoomer 740 tonight with this tonight...

Forgot to mention earlier that the manual tuning knob on this works much better than the other auto-tuning sets I have---has just a tiny bit of slop, but not enough to cause a problem.

After passing my hand by back of set and noticing a dramatic improvement in weak AM signal reception, decided to pull off back cover and adjust ANT trimmer. Noticed that there was dried battery leakage residue on right side of bottom---and the trimmers were pointed downward and not easy to adjust without desoldering FM antenna wire and moving cover further out for access, so put it back together without adjustment until other projects finished...

Really like the powerful audio on this set...

John


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 Post subject: Re: Zenith RB-77T Automatic Station Seeking radio project...
PostPosted: Jul Sun 22, 2018 8:23 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 30517
Location: SoCal, 91387
That appears to be a terrific radio, John; I'll have to look into getting one.

Based on your hand capacitance improving reception, I'd suggest employing a tunable loop to increase sensitivity.

_________________
\\\\\\\\\\\\\\\\\\\\\\\\He Who Dies With The Most Radios Wins//////////////////


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 Post subject: Re: Zenith RB-77T Automatic Station Seeking radio project...
PostPosted: Jul Tue 24, 2018 12:06 am 
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Joined: Aug Wed 26, 2009 1:50 am
Posts: 1455
Location: Mesquite NV 89027 (from Coventry, UK)
Yet another auto tuning radio. I didn’t know that there were so many different models. I should probably add one to my collection.


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 Post subject: Re: Zenith RB-77T Automatic Station Seeking radio project...
PostPosted: Jul Wed 25, 2018 12:51 am 
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Joined: Jan Thu 14, 2016 9:29 pm
Posts: 42
Wouldn't mind one of those myself. I have a Sony 7FA-70W, which works very well, but I do like the styling of the Zenith.


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 Post subject: Re: Zenith RB-77T Automatic Station Seeking radio project...
PostPosted: Aug Wed 01, 2018 1:59 am 
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Joined: Oct Mon 26, 2009 10:02 pm
Posts: 5735
Location: Indianapolis, IN
Hey Guys---this would be a good signal-seeker to have with good performance and great audio ! Kinda modern looking for collection, but a neat set otherwise...

Got a good start on this project Sunday...

This radio had battery leakage which corroded the negative spring contact and drained from compartment into bottom of radio. Completely disassembled the back cover and detail cleaned all parts along with AC power cord. Removed corrosion from spring contact with brass "toothbrush" and small piece of fine Scotchbrite in dish-soap solution.

Replaced battery contact and FM antenna wiring with Teflon insulated wire long enough to allow back cover to lay flat when removed for easier servicing---kept all original for future owner. After reassembling back cover components, realized that AC cord had to pass through notch in battery compartment tray so had to remove it again !

Reinstalled the shell of extendable whip antenna ("innards" missing along with the pivot ball) until I can find complete antenna assembly like it for replacement...

Notice the interesting use of spring tensioned rollers for handle---really has a nice, smooth "slide" in and out of cabinet---especially after removing crud from handle ends and guides.

After substantial increase in weak signal level when passing hand in area of ferrite antenna rod, thought that adjusting the ANT trimmer would improve performance---turns out it was already peaked...

Did a bit more detail cleaning on front control panel, but will probably pull chassis one day to do it properly...

Looked at schematic and have an idea of why FM seek doesn't stop at signals---will troubleshoot and report when time allows...

This is a Japanese made set. Didn't think to look for date codes while inside and still would like to find an old advertisement to give an idea when it was made...

Project pics thus far below...

John


Attachments:
1ARF RB77 CAB BK PRTS CLN.jpg
1ARF RB77 CAB BK PRTS CLN.jpg [ 206.05 KiB | Viewed 1018 times ]
2ARF RB77 HANDLE TENSION ROLLER DETAIL.jpg
2ARF RB77 HANDLE TENSION ROLLER DETAIL.jpg [ 134.92 KiB | Viewed 1018 times ]
3ARF RB77 HANDLE TENSION ROLLER INSTLLD.jpg
3ARF RB77 HANDLE TENSION ROLLER INSTLLD.jpg [ 97.11 KiB | Viewed 1018 times ]
4ARF RB77 CAB BK CVR INS CLN.jpg
4ARF RB77 CAB BK CVR INS CLN.jpg [ 228.34 KiB | Viewed 1018 times ]
5ARF RB77 CAB BK CVR INS CLN ASSEMBLED.jpg
5ARF RB77 CAB BK CVR INS CLN ASSEMBLED.jpg [ 229.8 KiB | Viewed 1018 times ]
6ARF RB77 INS CLN.jpg
6ARF RB77 INS CLN.jpg [ 247.2 KiB | Viewed 1018 times ]
7ARF RB77 BK CVR CONNECTED CLN.jpg
7ARF RB77 BK CVR CONNECTED CLN.jpg [ 192.72 KiB | Viewed 1018 times ]
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 Post subject: Re: Zenith RB-77T Automatic Station Seeking radio project...
PostPosted: Aug Wed 01, 2018 3:13 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 30517
Location: SoCal, 91387
xrhonda91 wrote:
Hey Guys---this would be a good signal-seeker to have with good performance and great audio !

So John, I presume there's a minimum signal strength threshold that it will stop for, but not weak DX stations? Can that be adjusted, if one wanted to have it stop at every single station?

_________________
\\\\\\\\\\\\\\\\\\\\\\\\He Who Dies With The Most Radios Wins//////////////////


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 Post subject: Re: Zenith RB-77T Automatic Station Seeking radio project...
PostPosted: Aug Thu 02, 2018 1:22 pm 
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Joined: May Wed 01, 2013 10:05 pm
Posts: 1990
Location: Rayleigh, BC, CANADA
I have to agree with Colin, Yet another signal seeker I didn't know existed, Neat set!

Typical Zenith flat antenna rod and tuning cap.

John have you tried connecting an external long wire antenna to see if the seek works on FM?

Curious to see what you find out in your diagnosis.

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Rocco


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 Post subject: Re: Zenith RB-77T Automatic Station Seeking radio project...
PostPosted: Aug Sat 04, 2018 4:07 pm 
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Joined: Oct Mon 26, 2009 10:02 pm
Posts: 5735
Location: Indianapolis, IN
Richard---it does have a local/distance switch and in DX mode does seem to stop on all listenable AM stations if you have a "fast finger" on the seek button !

Rocco---seeking doesn't stop at all on FM band, even on strong signal. Do have the schematic thanks to Bob, and can see where problem may lie---just need to get out the scope when time permits... Really need to pull chassis to get knobs and cabinet front as clean as I'd like them...

John


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 Post subject: Re: Zenith RB-77T Automatic Station Seeking radio project...
PostPosted: Feb Mon 04, 2019 11:07 pm 
Member

Joined: Oct Mon 26, 2009 10:02 pm
Posts: 5735
Location: Indianapolis, IN
Hello All,

Decided to pull this set from shelf and play a bit... Had forgotten what an excellent performer it was, though sound just a bit too "bassy" even at max. treble. And noticed that the small amount of "slop" in tuning actually fine-tunes on AM band !

After Bob sent the service data, noticed the separate pots for AM & FM seek sensitivity and wondered if perhaps the FM pot was bad, but did nothing at that time since things were very busy here... So today pulled back cover and played with the FM adjustment. The pot was indeed bad over a small range of travel, so increased it just beyond the "dead area" and FM seeking now works fine---thankfully !

All functionally fine now, so thought about full disassembly to detail clean front panel inside & out... Looked at what was involved and decided to put it off again... Did clean what I could from the outside and it does look much better, but didn't take a pic...

Pic of faulty FM seek sens. pot below...

Bob---if your still watching, how's your audio at full treble ?

John


Attachments:
ARF FM SEEK SENS ADJ.jpg
ARF FM SEEK SENS ADJ.jpg [ 208.1 KiB | Viewed 224 times ]
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