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 Post subject: Re: Zenith RD7000Y T/O project---radio bug bit again...
PostPosted: Jan Wed 30, 2019 4:19 am 
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Joined: Oct Mon 26, 2009 10:02 pm
Posts: 5729
Location: Indianapolis, IN
Hello John,

Was listening to AM BCB at low volume after clipping one lead of cap---after the wild oscillations when volume increased, reattached it... If audio section the same using silicon transistors, perhaps I have a bad bypass cap elsewhere in circuit ??? Do you have both schematics to compare ? Completed radio this evening and it's working great on all bands. Tuning dial looks super with the LED lighting---will post pics and report when time allows...

John


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 Post subject: Re: Zenith RD7000Y T/O project---radio bug bit again...
PostPosted: Jan Thu 31, 2019 12:07 am 
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Joined: Aug Thu 23, 2018 1:11 pm
Posts: 28
The audio amplifiers of the two 7000 variants are essentially the same except for two areas: (1) the latest version (yours) places a 22 ohm resistor in shunt with the 33 ohm emitter resistance at the pre-driver transistor when WB band is selected, this raises the stage gain by a factor of about 2.5 presumably to account for the low modulation of WX band signals. Unless the wires to the bandswitch are close enough to wires carrying the audio output signals to provide significant level of coupling I would not expect this to be a problem however.

(2) The network from which the pre-driver base voltage in the later versions is better decoupled than in the early versions, a 1 uF capacitor is used to filter the voltage source. I presume this is an electrolytic. If this has gone open audio present on the B+ rail could couple into the pre-driver causing the oscillation. Might be worthwhile to either check the 1uF or just shunt it with a "known-good" part.

I agree that the 7000 is truly a good looking set, now if it just didn't WEIGH so much!

John


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 Post subject: Re: Zenith RD7000Y T/O project---radio bug bit again...
PostPosted: Jan Thu 31, 2019 3:00 am 
Member

Joined: Oct Mon 26, 2009 10:02 pm
Posts: 5729
Location: Indianapolis, IN
Thanks for the info, John---the radio is back together for now since it works so well, but may pull it apart sometime in future to replace electrolytics if the motivation arises... And you're right about it being a HEAVY set ! Even without the 9 "D" cells installed...

Hello All,

Finally finished this neat radio last night after a couple days and many hours after work of effort. The back cover was a project unto itself to disassemble and detail clean yesterday evening. The speaker grille alone took around a couple hours to remove some "splatter" residue and to go over several times with inside-out cotton sock and Windex until clean. The bottom panel inside crevices were filthy---had to repeatedly clean the front bright strip edge as every time it was blown off, more dirty water came out ! After vigorous cleaning and polishing, the brightwork turned out pretty well. Once assembled, it looks really nice---definitely an improvement over what it was !

Didn't replace electrolytics or make any adjustments whatsover---not even the ANT trimmer, and the radio just works great after some use ! My favorite low-power oldies "benchmark" station 70 miles away which is 30 kHz below a very strong nearby local comes in beautifully. Will probably "tweak" a bit this weekend to satisfy curiousity and post results... The LED dial lighting is excellent, not at all overpowering in the dark and still very effective in daylight---last project pic shows radio in operation...

The original owner's son (that I bought it from) said that his late father bought this radio new at Graysons in Keyser, WV. It appears from date codes that it was made in 1975 (which I think I'd mentioned earlier).

Below are the project pics in two "installments"---sorry that I forgot to take one of the chassis front once clean as I was hurrying to get it together before "playtime" ran out a couple days ago...

Hope to hear of others experiences with their sets as I know several here own variants of this model... And Ed---no leftover parts or hardware !

John


Attachments:
1ARF RD7000Y CAB BOT BOT CLN.jpg
1ARF RD7000Y CAB BOT BOT CLN.jpg [ 124.1 KiB | Viewed 282 times ]
2ARF RD7000Y HRDWR SPKR CAB BOT TOP CLN.jpg
2ARF RD7000Y HRDWR SPKR CAB BOT TOP CLN.jpg [ 222.19 KiB | Viewed 282 times ]
3ARF RD7000Y CAB PRTS CLN.jpg
3ARF RD7000Y CAB PRTS CLN.jpg [ 189.99 KiB | Viewed 282 times ]
4ARF RD7000Y CAB PRTS CLN2.jpg
4ARF RD7000Y CAB PRTS CLN2.jpg [ 230.58 KiB | Viewed 282 times ]
5ARF RD7000Y CAB W-SPKR INS CLN.jpg
5ARF RD7000Y CAB W-SPKR INS CLN.jpg [ 207.16 KiB | Viewed 282 times ]
6ARF RD7000Y TOP CVR PRTS CLN.jpg
6ARF RD7000Y TOP CVR PRTS CLN.jpg [ 206.82 KiB | Viewed 282 times ]
7ARF RD7000Y CMPLT INS.jpg
7ARF RD7000Y CMPLT INS.jpg [ 233.95 KiB | Viewed 282 times ]
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 Post subject: Re: Zenith RD7000Y T/O project---radio bug bit again...
PostPosted: Jan Thu 31, 2019 3:02 am 
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Joined: Oct Mon 26, 2009 10:02 pm
Posts: 5729
Location: Indianapolis, IN
Here are the remaining pics---please see previous post for 1st group...


Attachments:
8ARF RD7000Y REAR CVR INS CLN.jpg
8ARF RD7000Y REAR CVR INS CLN.jpg [ 199.26 KiB | Viewed 281 times ]
9ARF RD7000Y REAR CVR PRTS1 CLN.jpg
9ARF RD7000Y REAR CVR PRTS1 CLN.jpg [ 249.05 KiB | Viewed 281 times ]
10ARF RD7000Y REAR CVR PRTS2 CLN.jpg
10ARF RD7000Y REAR CVR PRTS2 CLN.jpg [ 246.06 KiB | Viewed 281 times ]
11ARF RD7000Y CMPLT REAR CVR INS.jpg
11ARF RD7000Y CMPLT REAR CVR INS.jpg [ 247.16 KiB | Viewed 281 times ]
12ARF RD7000Y CMPLT REAR CVR BK INS.jpg
12ARF RD7000Y CMPLT REAR CVR BK INS.jpg [ 226.11 KiB | Viewed 281 times ]
13ARF RD7000Y CMPLT REAR.jpg
13ARF RD7000Y CMPLT REAR.jpg [ 230.06 KiB | Viewed 281 times ]
14ARF RD7000Y CMPLT CLOSED FRT RT ANG.jpg
14ARF RD7000Y CMPLT CLOSED FRT RT ANG.jpg [ 248.28 KiB | Viewed 281 times ]
15ARF RD7000Y CMPLT FRT RT ANG.jpg
15ARF RD7000Y CMPLT FRT RT ANG.jpg [ 185.93 KiB | Viewed 281 times ]
16ARF RD7000Y CMPLT DIALITE ON.jpg
16ARF RD7000Y CMPLT DIALITE ON.jpg [ 211.54 KiB | Viewed 281 times ]
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 Post subject: Re: Zenith RD7000Y T/O project---radio bug bit again...
PostPosted: Jan Thu 31, 2019 3:28 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 1470
Location: Jackson, TN
John,

Congrats on a great find at a fantastic price. I look forward to your after action report covering the great performance and a shot of the new LED dial lamps.

Tim


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 Post subject: Re: Zenith RD7000Y T/O project---radio bug bit again...
PostPosted: Feb Fri 01, 2019 2:19 am 
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Joined: Oct Mon 26, 2009 10:02 pm
Posts: 5729
Location: Indianapolis, IN
Thanks Tim---took a lot of effort to get it looking good as mentioned above, but am now glad that I got it... Just need to find/make a dust cover since there's no room now in display cabinets or closet for it !

Forgot to mention earlier that I do have the complete log/chart book, though it's missing the plastic binding strip. It's so musty smelling that I put it into a loosely-tied bag in utility closet until pages can be carefully wiped off and spread out in the sunshine this summer...

John


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 Post subject: Re: Zenith RD7000Y T/O project---radio bug bit again...
PostPosted: Feb Fri 01, 2019 12:23 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 20188
Location: Utica, NY 13502 (USA)
My Royal 7000, found for $5 in a box of lesser radios piled in a box at an estate sale, came with a fitted, clear plastic cover. I'm not sure if this was originally included with the radio when purchased or if it was an optional accessory.

You might want to reconsider replacing the electrolytics. I agree that the 1 uf cap (mentioned in an earlier post) is likely bad and is the cause of the oscillation.

Dave


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 Post subject: Re: Zenith RD7000Y T/O project---radio bug bit again...
PostPosted: Feb Sat 02, 2019 3:34 am 
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Joined: Oct Mon 26, 2009 10:02 pm
Posts: 5729
Location: Indianapolis, IN
Hello Dave,

Think I've seen those clear vinyl covers in a couple of Ebay listings---would definitely keep the dust out... The radio oscillated only when I disconnected that .003 uF at base of audio pre-driver---it works fine at all volume levels otherwise. But may replace electrolytics if I have to pull chassis for any other reason... That was probably the best $5 you've ever spent !

John


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 Post subject: Re: Zenith RD7000Y T/O project---radio bug bit again...
PostPosted: Feb Sun 03, 2019 2:50 am 
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Joined: Oct Mon 26, 2009 10:02 pm
Posts: 5729
Location: Indianapolis, IN
Hey Tim,

Went inside again and did a little tweakin'---slight adjustment of the ANT & mixer trimmers made a noticeable, but small improvement and the IFT's were all nearly dead-on as they were. This radio is outstanding on the AM BCB. Just would like the audio to be a bit "cleaner", but maybe new electrolytics will make a difference one day... Has anyone done a complete electrolytic replacement on one of these and noticed a worthwhile improvement in audio quality ??? Brett mentioned those poly caps in tone control circuit---is that "heaviness" also noticed at "full" treble position ???

Took a couple more pics of the dial lighting---to me, this is now a favorite feature of the radio (at least visually) !

John


Attachments:
ARF D7000Y DIALITING1.jpg
ARF D7000Y DIALITING1.jpg [ 228.03 KiB | Viewed 228 times ]
ARF D7000Y DIALITING2.jpg
ARF D7000Y DIALITING2.jpg [ 184.82 KiB | Viewed 228 times ]
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 Post subject: Re: Zenith RD7000Y T/O project---radio bug bit again...
PostPosted: Feb Sun 03, 2019 5:09 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 1470
Location: Jackson, TN
Looks great John!

With a little finessing, the LED panel lighting can be a great feature. Much reduced battery drain. The clear LEDs can be sanded then touched up with various Sharpie colors to get the desired effect.

Have fun with the new toy!
Tim


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 Post subject: Re: Zenith RD7000Y T/O project---radio bug bit again...
PostPosted: Feb Sun 03, 2019 5:14 am 
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Joined: Aug Wed 24, 2011 4:35 am
Posts: 4292
Location: Sunnyvale CA
xrhonda91 wrote:
Brett mentioned those poly caps in tone control circuit---is that "heaviness" also noticed at "full" treble position ???


Yes, the symptom I found was that it was "heavy" across the entire range of adjustment. Working normally, the center of the adjustment is typical Zenith "solid" but with the treble all the way up, it's pretty tinny.

The capacitors of interest are all below the switch panel, but if I can manage, I am sure anyone else can, too. I would very strongly recommend essentially shotgunning all the caps under the switch panel, because you have to do a bit of surgery to get to them at all, and you sure don't want to do it twice.

The 1 mfd caps that do the audio coupling are the most prone to going over the hill, the general rule being the smaller the physical size, the larger ratio of volume to surface area and a greater propensity to dry out.

Brett


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 Post subject: Re: Zenith RD7000Y T/O project---radio bug bit again...
PostPosted: Feb Sun 03, 2019 6:16 pm 
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Joined: Oct Mon 26, 2009 10:02 pm
Posts: 5729
Location: Indianapolis, IN
Thanks Brett !

I did have an "urging" to replace those caps as a preventative while I had control panel loose to check the RF-gain switch, but got lazy because radio seemed to work so well... When I pull chassis again, will probably replace all electrolytics as well as those you mentioned in tone circuit---and remove that RF-gain control to repair switch mechanism !

John


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 Post subject: Re: Zenith RD7000Y T/O project---radio bug bit again...
PostPosted: Feb Mon 04, 2019 9:24 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 20188
Location: Utica, NY 13502 (USA)
I've found that some radios that seem to work well with their original caps work or sound even better after the caps are replaced. There aren't very many electrolytics in this set.

Dave


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 Post subject: Re: Zenith RD7000Y T/O project---radio bug bit again...
PostPosted: Feb Mon 04, 2019 10:46 pm 
Member

Joined: Oct Mon 26, 2009 10:02 pm
Posts: 5729
Location: Indianapolis, IN
Thanks Dave---I noticed that while chassis was out, but was impatient to get it back together ! Am regretting it now, but not that hard to remove compared to others...

John


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 Post subject: Re: Zenith RD7000Y T/O project---radio bug bit again...
PostPosted: Feb Thu 07, 2019 6:09 am 
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Joined: Jan Sun 06, 2008 3:28 am
Posts: 4249
Location: Richmond, VA
Your dial light looks great! I replaced the electrolytic in a first version Royal 7000 a few years back, but had very poor sensitivity even after the recap. I didn't have the patience to sort through the numerous .o5 uF ceramic disc caps to see if one of them was the cause, and it was pretty beat up as well, so I let it go.

I have a really nice looking RD7000Y now that probably could benefit from new caps. I have also noted what you are describing as "heavy" sound. it must be common to this model.

_________________
Ed


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 Post subject: Re: Zenith RD7000Y T/O project---radio bug bit again...
PostPosted: Feb Thu 07, 2019 4:03 pm 
Member

Joined: Oct Mon 26, 2009 10:02 pm
Posts: 5729
Location: Indianapolis, IN
Thanks Ed !

Am waiting for Copiertech to report on his replacement of that tone cap that Brett mentioned earlier before I dig in again...

John


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 Post subject: Re: Zenith RD7000Y T/O project---radio bug bit again...
PostPosted: Feb Mon 25, 2019 6:28 am 
Member

Joined: Oct Mon 26, 2009 10:02 pm
Posts: 5729
Location: Indianapolis, IN
Hello All,

After searching a couple times for an AC power cord for this radio and finding prices a bit high (to me), decided to modify the cord from my old little-used Norelco electric shaver to fit.

Carefully sanded down the two narrow edges of connector with 220-grit sandpaper to fit opening in back cover, used 2000-grit for smoother surface, then finished by polishing with Novus-2. The hole spacing on connector just a tiny bit wider than radio pins, but it fit fine.

Plugged in and radio dead ! Pulled back cover and found that there was voltage present at switch terminal wired to PS, but not at center which "feeds" radio. Removed switch and saw that contact was covered in green residue. Cleaned with Windex and Q-tip, rubbed off as much oxidation as possible using end of Q-tip shaft dipped in DeOxit Gold liquid, then applied a bit to both contact surfaces. Re-installed switch, exercised it a few times, plugged in modified cord and all now fine ! Radio works great using internal AC supply with no noticeable hum or noise.

Just an idea for those who are missing their AC cords !

Pic below...

John


Attachments:
ARF NORELCO TO 7000 PWR CORD 2-24-19.jpg
ARF NORELCO TO 7000 PWR CORD 2-24-19.jpg [ 180.96 KiB | Viewed 89 times ]
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