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Old 06-14-2015, 06:37 PM
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Jeffhs Jeffhs is offline
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Zenith T-O 3000 wall-wart question

I have a Zenith Trans-Oceanic 3000-1 all-band radio, an eBay score about a year and a half ago. It works well, but I am wondering whether this radio uses a positive- or negative-ground wall-wart; that is, is the tip of the plug at the end of the cable positive or negative? (This question was answered in another post, but I haven't found it yet.) I would like to wire the wall wart permanently to the radio, as I don't carry it around at all (too heavy). I wonder about the ground on the wall wart because of something I read here in VK some time ago, that if the wall-wart plug is wired backwards, it can destroy the audio output transformer and the output transistors. This radio sounds great on FM, so I don't want to put it completely out of commission.

Also, I am wondering about a loose wire I found on the battery case. The schematic shows it as being connected to the negative battery terminal, but the battery case in my set does not have such a terminal (this radio was modified by its previous owner to use a rechargeable NiCad battery pack, so the battery box is not original; there is also a battery fuse in series with the positive lead to the pack). If need be, I will use the battery box from my Zenith T/O 1000-1, but if the 3000's can be rewired I'd just as soon use it.

Thanks for any and all replies.
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Last edited by Jeffhs; 06-14-2015 at 06:49 PM.
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Old 06-14-2015, 08:25 PM
dieseljeep dieseljeep is offline
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Quote:
Originally Posted by Jeffhs View Post
I have a Zenith Trans-Oceanic 3000-1 all-band radio, an eBay score about a year and a half ago. It works well, but I am wondering whether this radio uses a positive- or negative-ground wall-wart; that is, is the tip of the plug at the end of the cable positive or negative? (This question was answered in another post, but I haven't found it yet.) I would like to wire the wall wart permanently to the radio, as I don't carry it around at all (too heavy). I wonder about the ground on the wall wart because of something I read here in VK some time ago, that if the wall-wart plug is wired backwards, it can destroy the audio output transformer and the output transistors. This radio sounds great on FM, so I don't want to put it completely out of commission.

Also, I am wondering about a loose wire I found on the battery case. The schematic shows it as being connected to the negative battery terminal, but the battery case in my set does not have such a terminal (this radio was modified by its previous owner to use a rechargeable NiCad battery pack, so the battery box is not original; there is also a battery fuse in series with the positive lead to the pack). If need be, I will use the battery box from my Zenith T/O 1000-1, but if the 3000's can be rewired I'd just as soon use it.

Thanks for any and all replies.
IIRC, the set requires 12VDC @ around 1.0 amp.
Is there a external power jack on the radio. Going by memory again, it seemed that the jack was smaller, than the earphone jack, like 2.5 mm and the tip was negative. The AC adaptor, I picked up for it, had reversed polarity, so I had to change it, by cutting and resplicing the cable for the proper polarity. It was done neatly by staggering the splice and using heat-shrink sleaving. The owner understood, that was the only way it could be done, as the case of the adaptor was securely glued together and couldn't be opened without destroying it.
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Old 06-15-2015, 12:10 AM
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Electronic M Electronic M is offline
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Why not touch a voltmeter to the 12V plug with the wall wart plugged in and find out the polarity yourself? I can't imagine a Ham/radio collector like you not having a DMM or VOM.
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Old 06-15-2015, 01:11 PM
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Quote:
Originally Posted by Jeffhs View Post
I am wondering about a loose wire I found on the battery case. The schematic shows it as being connected to the negative battery terminal, but the battery case in my set does not have such a terminal (this radio was modified by its previous owner to use a rechargeable NiCad battery pack, so the battery box is not original
The original plug that connects the battery pack to the radio had 3 wires:

Green = Negative for the radio.
Black = + 12 V for the radio power and shared common (negative) for the dial light battery... connects to chassis ground.
Brown= + 1.5 V for the dial lights.

I suspect that the extra wire is the brown wire, likely the dial lights have been connected internally through a resistor, the 12 V nicad pack powers both. (LED mod, perhaps?).

jr
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Old 06-15-2015, 01:55 PM
old_coot88 old_coot88 is offline
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I have a 3000-1 that didn't have a wall wart when I got it. So ended up using a 9V-rated DC wallwart, which puts out a little over 13V no-load, which drops to about 12V with the radio turned on. The radio is very happy with this.
The current draw is nowhere near 1A, but somewhat less than 50 ma IIRC. The brown wire is for the dial lites, which are on a momentary switch, and operate only in battery mode.
The reverse polarity is because the transistors are all PNP type ('stead of NPN).

And a heads up to anybody using one of these sets on battery: The battery feed-thru jack is a phenolic wafer sandwich, and develops leakage between lugs and from lugs to chassis. Mine measured 200 microamps to chassis (that's with the radio turned off, of course).
I had to get rid of the whole assembly, and since no replacement's available, made a new plug and jack set using RC model airplane connector parts.
Another 3000-1 owner also mentioned leakage in the battery jack.

Last edited by old_coot88; 06-15-2015 at 05:33 PM.
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Old 06-15-2015, 07:27 PM
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Jeffhs Jeffhs is offline
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Quote:
Originally Posted by Electronic M View Post
Why not touch a voltmeter to the 12V plug with the wall wart plugged in and find out the polarity yourself? I can't imagine a Ham/radio collector like you not having a DMM or VOM.
I do have a DMM, and will use it to determine the polarity of the wall wart. However, what I was planning to do was to hard-wire the wall wart directly to the radio, bypassing the adapter jack altogether. The schematic isn't too clear on how to do that, and as I said, I don't want to destroy the audio output transformer, output transistors or both by using the wrong side of the wall wart output as ground. There was a post here in this forum quite a while ago which addressed this very issue, stating if the ground connection is made to the wrong terminal of the AC adapter jack (or the plug on the wall wart output cable is wired such that the wrong side of the circuit is grounded), the parts I mentioned will be instantly destroyed. If anyone remembers where that post is, I'd appreciate the information so I can look it up. I think the T/O 3000's AC adapter has a positive ground, but I am not sure and don't want to find out the hard way--by burning up several parts of the radio that may now be NLA, after almost 50 years.
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Old 06-15-2015, 08:37 PM
old_coot88 old_coot88 is offline
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If you're gonna hardwire the wallwart in, just be sure the positive wire from the WW goes to the chassis ground.
Here's the full service manual which might be useful. See page 12 for the area in question..
http://www.manualslib.com/manual/692...page=12#manual
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Old 07-27-2015, 12:04 AM
transmaster transmaster is offline
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I would restore it to the original battery pack. The orginal Carbon Zinc "D" cells were good for some where around 500 hours, modern alkaline batteries considerably longer. So long in fact some people record on each battery the date installed so they can be changed out to prevent any chance of battery leakage. I have no intention of using anything but batteries in any of my SS ZTO's including the Royal 7000.
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