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 Post subject: Royal 500 Fades - (Not Electrolytics)
PostPosted: Jan Fri 17, 2020 2:49 am 
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Joined: Jan Thu 09, 2020 6:46 am
Posts: 3
After my wife gave me a Trans-Oceanic D7000Y for Christmas (which I've physically cleaned up and will recap), I thought I would also restore a Royal 500 that my godmother gave to me years ago. It worked, but faded after a few minutes. I bought a "re-cap kit" from a guy on eBay (I wanted his notes, etc., I know it was only a few dollars of capacitors, support the hobby), and recapped it. The radio sounded better and a loud volume problem cleared up, but the radio would still fade after a few minutes of operation. I didn't have the "it worked until I recapped it" problem, so I can't be a COMPLETE idiot :)

I was thinking that it was a weak/failing transistor, so I bought some on eBay BEFORE learning that my particular radio did not have the usual transistors:

Royal 500 (b?)- 7ZT40Z1
Osc = 121-15 or 16, illegible
Mixer 121-13
IF's = 121-17
Driver=121-18
Outputs = 121-19

I bought replacement transistors for the outputs (unfortunately AFTER I found about the transistor differences). They are "equivalent" to the NTE102, not the 102A, so they have less power capacity. Nonetheless, I substituted the -18 and -19's and still have the same problem. So, it's probably not the amplifier.*

What should my next course of action be? TIA

* I was wondering about the .1uf capacitor across the outputs. What is its purpose. Can it go bad? I could remove it and measure it but it's pretty delicate in there and i don't want to just start desoldering parts. It is yellow and has a stripe on it as though it is polarized but the schematics don't seem to indicate that this is true.


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 Post subject: Re: Royal 500 Fades - (Not Electrolytics)
PostPosted: Jan Fri 17, 2020 5:12 am 
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Joined: Oct Mon 02, 2017 8:53 am
Posts: 266
Location: Panama City, FL 32401
I just looked at a 500B that has the same chassis. 7ZT40Z1
Osc=121-15
Mixer=121-16
1st,2nd IF's=121-17
Driver=121-18
Outputs=121-19

I've had that happen too after a radio has been playing to slowly fade. Usually is a weak transistor.


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 Post subject: Re: Royal 500 Fades - (Not Electrolytics)
PostPosted: Jan Fri 17, 2020 5:20 am 
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Joined: Jan Tue 31, 2012 1:55 am
Posts: 10856
Location: Mountains of Mourne. Ireland.
You have tried using fresh batteries?

The guy on eBay - - was his name Fast Eddie. lol
Greg.

Edit: some bedtime reading...
https://www.americanradiohistory.com/Ar ... Lemons.pdf


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 Post subject: Re: Royal 500 Fades - (Not Electrolytics)
PostPosted: Jan Fri 17, 2020 5:45 am 
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Joined: Oct Mon 02, 2017 8:53 am
Posts: 266
Location: Panama City, FL 32401
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I don't know what that .1uf cap does,but they don't seem to be an issue, so I leave them as is. They're in many of the Zeniths I have. Being a .1uf, it wouldn't be an electrolytic. At least I've never seen one below 1uf.


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 Post subject: Re: Royal 500 Fades - (Not Electrolytics)
PostPosted: Jan Fri 17, 2020 8:31 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 33625
Location: SoCal, 91387
Zenith 500 front end Transistors;

Converter, 2N94 (NTE 103A), GE 2N169 (NTE 101)

IF's, 2N94 (NTE 103A), GE 2N169A (NTE 101)

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


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