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 Post subject: Re: Zenith Royal 500 being purchased
PostPosted: Sep Thu 10, 2020 8:43 pm 
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Joined: Aug Wed 24, 2011 4:35 am
Posts: 5166
Location: Sunnyvale CA
IZ5WWB wrote:
Here it is. It looks like a chassis 7XT40Z1.
The volume pot could have been replaced (not sure). The shaft has a threaded hole in the center and looks badly re-worked to make it fit the original knob. The radio receives a local AM station but the audio level is very low.
All in all, not a great deal for 80 euros I think.

https://drive.google.com/drive/folders/ ... sp=sharing

Best regards
Daniele


If it still has the original electrolytic caps, those are nearly universally dead now, which is probably why it has low volume. You can test that by bridging them temporarily, if you don't want to replace the originals (which is what I did in mine). The ones that cause low volume are the two coupling caps, 5mfd, I think, going to the audio driver and to the volume control pot.

I haven't looked carefully at which volume control pot this radio uses, it is possible I have one from a parts radio. If it's the same, and I have one, I will just send it to you.

Give me a day or two to check.

Brett


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 Post subject: Re: Zenith Royal 500 being purchased
PostPosted: Sep Thu 10, 2020 9:08 pm 
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Joined: Aug Sat 16, 2014 2:19 am
Posts: 1783
Location: Palos Verdes, CA
Zenith Royal - I replaced the 121-19 transistor in my 7XT40Z with a Motorola 2N145 and was surprised that it worked quite well, although trying a NTE-102A did nothing. However, the NTE-102A did work as a replacement for the 121-18 transistor. - Mark


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 Post subject: Re: Zenith Royal 500 being purchased
PostPosted: Sep Thu 10, 2020 9:16 pm 
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Joined: Sep Fri 14, 2018 11:18 pm
Posts: 16
3Transistors wrote:
As for the volume control, the type used in your Zenith 500 has a 1/8 inch shaft and they are available on eBay. I had to replace the volume control in a Zenith 500H, which has a 1/16 inch shaft and found an affordable substitute after quite a search as there seem to be few switches that would fit. - Mark


Hi Mark, I found on eBay.com exactly the same type of volume pot which is currently mounted on the radio.

https://www.ebay.com/itm/NOS-Vintage-19 ... 3715914493

It is 25 kohms (not a problem), but it has a round shaft, so it would require some metal work to make it flat :roll:

I found not that easy to find an audio potentiometer w/ switch and a 1/8" flat shaft.

BR
Daniele


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 Post subject: Re: Zenith Royal 500 being purchased
PostPosted: Sep Thu 10, 2020 9:18 pm 
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Joined: Sep Fri 14, 2018 11:18 pm
Posts: 16
3Transistors wrote:
Zenith Royal - I replaced the 121-19 transistor in my 7XT40Z with a Motorola 2N145 and was surprised that it worked quite well, although trying a NTE-102A did nothing. However, the NTE-102A did work as a replacement for the 121-18 transistor. - Mark


Thanks Mark for sharing your results.

Best regards
Daniele


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 Post subject: Re: Zenith Royal 500 being purchased
PostPosted: Sep Thu 10, 2020 9:22 pm 
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Joined: Sep Fri 14, 2018 11:18 pm
Posts: 16
Brett_Buck wrote:
I haven't looked carefully at which volume control pot this radio uses, it is possible I have one from a parts radio. If it's the same, and I have one, I will just send it to you.

Give me a day or two to check.

Brett


Thanks a lot Brett for your support.

BR
Daniele


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 Post subject: Re: Zenith Royal 500 being purchased
PostPosted: Sep Thu 10, 2020 10:57 pm 
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Joined: Aug Sat 16, 2014 2:19 am
Posts: 1783
Location: Palos Verdes, CA
Daniele - I found a potentiometer that would probably fit in your Zenith 500, but you would have to cut the shaft:

https://www.ebay.com/itm/One-NOS-NIB-Ph ... Swf-VWZZ25

I made a mistake earlier as the shaft on the Zenith 500H is 1/8 inch and not 1/16 inch. - Mark


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 Post subject: Re: Zenith Royal 500 being purchased
PostPosted: Sep Fri 11, 2020 3:13 am 
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Posts: 36212
Location: SoCal, 91387
3Transistors wrote:
Daniele - I found a potentiometer that would probably fit in your Zenith 500, but you would have to cut the shaft:

https://www.ebay.com/itm/One-NOS-NIB-Ph ... Swf-VWZZ25

I made a mistake earlier as the shaft on the Zenith 500H is 1/8 inch and not 1/16 inch. - Mark

I'm not sure that pot would fit, given it's height.

Daniele, I would suggest messaging the seller of any pot you might want to buy, and ask for it's height, from the back of the switch to the front of the volume control.

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


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 Post subject: Re: Zenith Royal 500 being purchased
PostPosted: Sep Fri 11, 2020 12:00 pm 
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Joined: Sep Fri 14, 2018 11:18 pm
Posts: 16
3Transistors wrote:
Daniele - I found a potentiometer that would probably fit in your Zenith 500, but you would have to cut the shaft:

https://www.ebay.com/itm/One-NOS-NIB-Ph ... Swf-VWZZ25

I made a mistake earlier as the shaft on the Zenith 500H is 1/8 inch and not 1/16 inch. - Mark


Thank you, Mark. Unfortunately the item description specifies that this pot has a 1/4" shaft.
BR
Daniele


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 Post subject: Re: Zenith Royal 500 being purchased
PostPosted: Sep Fri 11, 2020 11:13 pm 
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Joined: Sep Fri 14, 2018 11:18 pm
Posts: 16
Hello all,

here is the photograph of the volume pot surroundings.

Attachment:
IMG_20200911_234201.jpg
IMG_20200911_234201.jpg [ 549.09 KiB | Viewed 183 times ]


The capacitor pointed by the yellow arrow is the one responsible for the low audio level (3 uF, 6V), I will replace it soon. One of the other three electrolytics had been already replaced (a 100 uF modern capacitor is present in place of the original 50 uF).

The volume pot works fine, but it has a 1/8" shaft, while I have discovered that it should be 1/4", D shape. In fact, an attempt was made to build a "spaghetti" adapter (by wrapping a small piece of steel foil around the top end of the shaft, with the addition of a screw through the center of the knob), which ended up with destroying the knob itself.

Moreover, the pot is not mounted on the chassis by the usual threaded mount. It is soldered to the chassis directly and has no threaded mount at all (quite an unusual kind of potentiometer).


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 Post subject: Re: Zenith Royal 500 being purchased
PostPosted: Sep Sat 12, 2020 1:40 am 
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Joined: Aug Sat 16, 2014 2:19 am
Posts: 1783
Location: Palos Verdes, CA
I decided to get my calipers and measure the potentiometer shaft diameter on my Zenith Royal 500 7XT40Z1 and it was 0.188 inch, the same diameter as on my 7ZT40Z. The overall length of the 7XT40Z1 switch was 1.18 inches, with the switch body 0.47 inch. The potentiometer on the 7XT40Z1 is soldered to the metal chassis, with the switch on the 7ZT40Z1 fastened with a nut. The switch overall length on the 7ZT40Z1 is 1.35 inches.

In order to get my Zenith 500 7XT40Z1 working, you can see that I installed a 10 uf electrolytic capacitor.

Sorry that I probably caused some confusion as the Zenith 500 uses a potentiometer with a 1/8 inch shaft, with the Zenith 500H using a smaller 1/16 inch shaft. - Mark


Attachments:
Zenith 500 7XT40Z1 potentiometer.JPG
Zenith 500 7XT40Z1 potentiometer.JPG [ 369.13 KiB | Viewed 175 times ]
Zenith 500 7XT40Z1 potentiometer 2.JPG
Zenith 500 7XT40Z1 potentiometer 2.JPG [ 316.88 KiB | Viewed 175 times ]
Zenith 500 7XT40Z1 potentiometer 3.JPG
Zenith 500 7XT40Z1 potentiometer 3.JPG [ 350.76 KiB | Viewed 175 times ]
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 Post subject: Re: Zenith Royal 500 being purchased
PostPosted: Sep Sat 12, 2020 8:46 am 
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Joined: Sep Fri 14, 2018 11:18 pm
Posts: 16
Hello Mark, thanks for the scans and figures about the volume pot.
So in my understanding the volume and tuning knobs were not interchangeable on 7XT40Z1, while I supposed they were.
I remember that I read that this changed at some point during the production of the different Royal 500 versions, but I cannot remember where I read this information.
As for the capacitors, I plan to replace the 3 uF with a 10 uF I have. This seems to solve the low audio level issue. Would you suggest to replace the remaining electrolytic caps as well? I tried to connect a 10 uF in parallel with the other old 3uF on the top left corner of the chassis and things got sensibly worse.
Best regards
Daniele


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 Post subject: Re: Zenith Royal 500 being purchased
PostPosted: Sep Sat 12, 2020 4:16 pm 
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Joined: Aug Sat 16, 2014 2:19 am
Posts: 1783
Location: Palos Verdes, CA
Daniele - The tuning knob on the 7XT40Z1 has a 1/16 inch shaft which is round, whereas the volume knob is 1/8 inch. The article below discusses when the Zenith 500 AB was introduced:

http://www.antiqueradio.com/Jul08_MacArthur_Royal.html

My 7XT40Z1 was the first Zenith 500 in my collection and is still the only one that I have with a metal chassis. I only replaced the one electrolytic capacitor to get the Zenith 500 working and it performs quite well. I'm not one to change all the electrolytic capacitors in a vintage transistor radio unless I have to do so in order to get it to work. I used a Zenith 3000-1 daily to listen to the radio with all original components and later switched to a Zenith 900. I bought a GE SuperRadio recently and now use it every day as I have it plugged into the wall and don't need to use batteries. - Mark


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 Post subject: Re: Zenith Royal 500 being purchased
PostPosted: Sep Sat 12, 2020 5:57 pm 
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Joined: Sep Fri 14, 2018 11:18 pm
Posts: 16
3Transistors wrote:
Daniele - The tuning knob on the 7XT40Z1 has a 1/16 inch shaft which is round, whereas the volume knob is 1/8 inch.

This is not my case, as on my Royal 500 the tuning capacitor shaft is larger than 1/8" in diameter and has a D shape. I'm certain it is original and the tuning knob matches perfectly with it.

3Transistors wrote:
I only replaced the one electrolytic capacitor to get the Zenith 500 working and it performs quite well. I'm not one to change all the electrolytic capacitors in a vintage transistor radio unless I have to do so in order to get it to work.

I have just done the same and now the audio level is fully satisfactory (though I have not attempted any re-alignment yet). I agree with you on keeping a working vintage radio as much original as possible.

3Transistors wrote:
I bought a GE SuperRadio recently and now use it every day as I have it plugged into the wall and don't need to use batteries. - Mark

By chance I also have a GE Superadio on my desk. Great sound!

Attachment:
IMG_20200912_185332.jpg
IMG_20200912_185332.jpg [ 666.19 KiB | Viewed 125 times ]


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 Post subject: Re: Zenith Royal 500 being purchased
PostPosted: Sep Sat 12, 2020 6:29 pm 
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Joined: Aug Sat 16, 2014 2:19 am
Posts: 1783
Location: Palos Verdes, CA
There was another Zenith 500 7XT40Z1 that had the later tuning capacitor:

viewtopic.php?f=4&t=278892

My 7XT40Z1 may have been previously modified as the case is "translucent," but the cover is not.

My GE radio is the later version III, which I bought from a seller on eBay from Southern California who does an excellent job in packaging his radios. The seller uses the most economical means to ship the radio and I don't have a problem waiting. - Mark


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