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 Post subject: Zenith Royal 200 info
PostPosted: Sep Fri 30, 2005 3:02 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 794
Location: Gulf Breeze, FL USA
Hello solid state guru's. I hope I don't have to change my handle to "Emitter Follower" in order to post over here on the transistor forum. Today I acquired the subject radio after it just seemed to cry out to me from the junk shop shelf. I picked it up and it was heavy, old, made in the USA, and very nostalgic, so even a tube guy like me couldn't leave it there. So this will be my first transistor restoration. It almost plays. Sounds like an untuned TRF as you go across the dial, but never detects the modulated signal. So, here are the questions:<BR>1)Where to get service data? Struck out at Nostalgia Air, but web searching turned up this - Chassis # 7AT48Z, Model ref #72381, <BR>Sam's TSM Vol 6 Page 139, Beitman's 1959.<BR>2) Even without service data, I suppose I should replace at least the electrolytic and tubular caps; should the "mica's" (thin, about the size of a dime) also be replaced? If so, with what type cap?<BR>At least I won't have to dig these out of a can full of tar like my Philco 96 project!<BR>Thanks in advance for any/all help. <BR>Ben Gray<P>------------------<BR>


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 Post subject: Zenith Royal 200 info
PostPosted: Sep Fri 30, 2005 6:39 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 12310
Location: Albuquerque, NM 87123
The Royal 200 is in Photofact 455, which I am missing.<P>------------------<BR>


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 Post subject: Zenith Royal 200 info
PostPosted: Sep Fri 30, 2005 9:15 am 
Inactive

Joined: Jan Thu 01, 1970 1:00 am
Posts: 65
Location: Somerset, NJ USA
Ben,<P>I've fixed numerous transistor radios without service data. >80% of problems are open capacitors, the remainder are leaky transistors, broken parts(resistors, etc).<BR>The disk capacitors almost never fail unless they are cracked or damaged. I think the 200 has 3 or 4 Nashville electrolytic capacitors in it.<P><BR>This is what I do....<P>-Check components for visable damage...<BR>-Shunt a fresh capacitor in parallel under the board and listen for improvement to identify open caps<BR>-Make sure it ocillates(It should oscillate with an open cap but not with a bad transistor)<BR>-Check transistors for leakage. The 200 has plug ins so this is simple<P>Usually the above would identify the problem. If it doesn't, I check the power consumption on a metered power supply. It should be under 15ma with the vol all the way down. It should be stable too, not rising when it warms up. <BR>If all this still failed to idenify the problem, then the service data would be needed. <P>I kept the original caps on mine and mounted caps under the board. Transistor collectors prefer the original parts in place. <P>jim<P>------------------<BR>


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 Post subject: Zenith Royal 200 info
PostPosted: Oct Sat 01, 2005 1:19 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 794
Location: Gulf Breeze, FL USA
Hi all.<BR>Johnnysan, thanks for looking.<P>Brian, here's the lineup from the layout on the inside of the back panel:<BR>121-91 - osc; 121-92 - mixer; 121-93 - 1st IF; 121-94 - 2nd IF; 121-95 - driver; 121-96 (2ea) output. This agrees with the parts found in the unit and all are in the correct positions.<BR>Thanks for looking.<P>Jim, no obvious physical damage to parts.<BR>Got some capacitors from the sorry selection at RS and will try the parallel hookups tonight. I think its oscillating because I get all the howls and squeals as its tuned across the dial. Mixer may be generating the wrong IF, or the osc may have drifted. Both of my tube testers have transistor socket on them,so I guess I'll learn how to use them.<BR>Thanks for pointing out that they plug in as I hadn't noticed that. The caps all seem to be the ceramic type except for a can type that appears to have 2 sections at 50uf/1v,and 5ouf/6v; and two tubular caps with polarity marked that are 16uf/3v and 3uf/12v. These last two are white.I assume these 4 are electrolytics.<P>Thanks to all for the assist. I'll post progress as its made and continue to hope for a member with some service data.<BR>Ben Gray<P>------------------<BR>


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 Post subject: Zenith Royal 200 info
PostPosted: Oct Sat 01, 2005 3:35 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 65
Location: Somerset, NJ USA
Hi Ben,<P>The fact that it squeals means you have open capacitors. Those are the 4 caps<BR>you'll need to look into. When you shunt good caps, it'll start to play. Volume will increase too, then you can tweek it if it needs it. It may just be fine. <P>After open caps are identified, I mount tantalum caps on the board. They are tiny and fit well in tight spaces. They are a fraction of the size of aluminum capacitors. They cost about 10 cents each on Ebay. They come in 6 volts and 16 volts.<BR>The 200 is big, so aluminums should fit Ok.<P>take care<BR>Jim<P>------------------<BR>


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 Post subject: Zenith Royal 200 info
PostPosted: Oct Sat 01, 2005 4:25 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 794
Location: Gulf Breeze, FL USA
Hi Jim<P>Did a little troubleshooting with the following results:<BR>1) 400hz signal injected at the volume control plays clearly. Would seem to indicate that the 50uf electrolytics are OK since they appear to be in the output stage. (dual 121-96's, push-pull?)<BR>2)O'scope shows that its oscillating. Nice clean sine wave.<BR>3)Modulated 455khz signal injected at 1st and 2nd IF heard faintly. I may have had the sig-gen turned up too high and just blew it through these stages.<BR>4)What I assume to be the detector diode at the driver transistor checks good.<BR>5) Noticed that when first turned on, unit plays the noise from my shop light clearly for a second or two, then starts howling.<BR>Does this sound like caps, or transistors?<BR>6) Tried cap substitution with existing caps in place, but no one substitution caused the unit to play.<P>Tomorrow will replace all electrolytics (anyway) and test the transistors.<P>Thanks for the continuing dialog.<BR>Ben<P>------------------<BR>


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 Post subject: Zenith Royal 200 info
PostPosted: Oct Sat 01, 2005 4:48 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 794
Location: Gulf Breeze, FL USA
Thanks Brian.<BR>I saw and bookmarked the NTE X-ref that you posted on this forum when I first came over here, just in case I needed to replace some transistors. Here's hoping that the caps will do the job.<BR>Ben<P>------------------<BR>


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 Post subject: Zenith Royal 200 info
PostPosted: Oct Sat 01, 2005 6:20 am 
Inactive

Joined: Jan Thu 01, 1970 1:00 am
Posts: 65
Location: Somerset, NJ USA
Hi Brian,<P>Wow that's thorough testing. The fact that when injected, the IF tone being heard with low volume might indicate an open cap in that section. The audio section is fine, it's oscillating, sounds like it's close to playing. I would bet on capacitors. That big 50uf can is probably OK since the audio is good. it's the smaller white/red EIA caps that are the culprits. <P>I wouldn't jump to conclusions about bad transistors until it's recapped. After recap,a leaky transistor usually causes the radio to play<BR>until it warms up, then it'll fade out. Power consumption also starts out normal,<BR>about 10ma, then gradually rises through warmup.<P>I agree with Brian on those NTE transistors. I had a leaky oscillator transistor in my Royal 500 and replaced it with the NTE version and it plays fine now.<P>I have a parts 200 set somewhere. If you need some parts, let me know and I'll see what's left. I think I have most of the transistors.<P>Take care<BR>Jim <P>------------------<BR>


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 Post subject: Zenith Royal 200 info
PostPosted: Oct Sat 01, 2005 6:27 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 65
Location: Somerset, NJ USA
Oops...meant to say Hi Ben<P>------------------<BR>


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 Post subject: Zenith Royal 200 info
PostPosted: Oct Sun 02, 2005 6:03 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 794
Location: Gulf Breeze, FL USA
Hi Guys.<BR>Well, I lied. Really meant to replace the electrolytics today, but A)couldn't find replacements, and B) went off antiquing/radio searching and wasted most of the day. Had a good time though!<BR>Anyhow, when I got home, tried another round of substituting caps and listening for improvement, once again to no avail. So I broke out my trusty EICO 667 tube tester, and tested the signal transistors, 121-91 through 121-94. Since they all translate to NTE 100's<BR>I expected the performance to be about the same for all 4. Not so. The 121-92 mixer was off the scale on the Ico test,(grounded emitter,no signal at base) and much higher than the others on the DC Beta test.<BR>So, looks like I've got a bad transistor.<BR>I'll start beating the bushes for a source of the NTE-100. Sure like to buy it locally and save the shipping time.<BR>Cheers!<BR>Ben Gray<P>------------------<BR>


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 Post subject: Zenith Royal 200 info
PostPosted: Oct Sun 02, 2005 8:34 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 21
Location: BARRINGTON, ILL, USA
Hi Ben,<P>I looked in my files and I see that I have a Sam's photofact schematic for your Zenith Royal 200. However, I can not scan this image in and e-mail it, for my scanner is broken. But, I would be happy to answer any technical questions that you may have on this radio's schematic. It looks like it uses (7) RCA PNP germanium transistors with<BR>a (+) Positive chassis Ground. So, make sure that you watch your polarities with the electrolytics. And in this case, the (+) end will go to chassis ground, for this particular circuitry has a (+) Positive Ground chassis. And also, I would automatically install all new electrolytics for they are most likely "Bad" and will cause major proformance problems. <BR>The 16uF cap. is the AVC filter. And the 3uF cap. is the Audio coupling cap. And finally, the (2) 50uF caps are the Main battery supply line filter and also the Audio Driver's emitter bypass filter. And finally, it is "Okay" to couple new ones under the chassis and leave the old ones in place, as long as you make sure that one of the leads is disconnected on each of the old ones. This is just in case that the old ones is either "Leaky" or "Shorted", instead of just being open. The Leaky (Icbo) mixer transistor is a RCA 2N411, as shown in the schematic. After replacing all of the electrolytics and the "Leaky" mixer/converter transistor, you should be able to start hearing your favorite tunes again. And by the way, this circuitry does NOT use the emitter-followers, it uses common-emitter grounds in this circuitry.<P>Rickster<P>------------------<BR>


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 Post subject: Zenith Royal 200 info
PostPosted: Oct Sun 02, 2005 7:08 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 794
Location: Gulf Breeze, FL USA
Hi Rickster,<BR>Thanks for looking and for providing the technical circuit description. I had noticed the positive chassis, which is really unusual to an old tube guy like me. I'm also scratching my head over why a battery supply needs filtering, but hey, I just gotta fix 'em, I don't have to understand 'em. <P>As for the schematic, fellow member DJBILLY has kindly supplied me with the Zenith Service Manual, which will be invaluable in this repair, so I'm no longer in the dark.<BR>Thanks again DJBILLY!<P>Guess I'll get out the Mouser catalog and gen up an order.<P>Cheers!<BR>Ben Gray<P>------------------<BR>


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 Post subject: Zenith Royal 200 info
PostPosted: Oct Mon 03, 2005 12:01 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 21
Location: BARRINGTON, ILL, USA
Hi Ben,<P>Tube technology and transistor/semiconductor technology is very similiar, but can also differ. With the early 50's germanium junction transistors, you will have either a NPN or PNP type, which acts like a triode tube. Most of the 50's transistor radio designs used the commom-emitter ground configuation, which gives you the most beta gain or amplification. So, if you are using PNP types, then the emitter which needs positive voltage supply, must be hooked up to the positive side of the battery. So, with PNP types, you will usually see the polarity of the battery supply switched, where the Positive side goes to chassis ground, giving it a (+) Ground. Now, if you hook up the emitter of the PNP type to the Positive side, you will also have the emitter at common potenial ground, giving it a common-emitter configuation.<BR>Although, you could hook up PNP types with negative grounds, but instead of getting a common-emitter configuation, you will get a common-collector or emitter-following configuation. The common-collector configuation is less beta or amplification gain then the common-emitter configuation, but it is much more stable as an amplifier, where neutralization or negative feedback is less likely needed. And you will almost always see the NPN types hooked up to the<BR>more common (-) ground chassis, which will also give you a common-emitter configuation.<P>And finally, the Main line battery supply bypass electrolytic capacitors, which is usually 50 uF and higher, is very important.<BR>This filter will keep the RF/IF/AF signals<BR>in its own path and out of the DC voltage supply lines. This filter also acts a the main ground path for all of the bypass capacitors used in the circuitry. You will also see these Main Filter electrolytic caps in Tube radios, except they will be in a Big metal can that will often have dual electrolytic capacitors built into it. But, this device serves the same purpose as in the battery operated radios.<P>I hope that the above information will give you some more insight on transistor technology.<P>Rickster<BR><P>------------------<BR>


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 Post subject: Zenith Royal 200 info
PostPosted: Oct Mon 03, 2005 12:31 am 
Silent Key

Joined: Jan Thu 01, 1970 1:00 am
Posts: 34328
Location: Sandpoint, IDAHO 83864
I don't do much with solid state stuff, but the main capacitor to change in my opinion is the one bypassing the battery, like Rickster said. If it opens up or loses value and your batteries have any internal resistance, the audio signals will couple back thru the rest of the set and you will get howls, squeals, motorboating, thumping, and just about all other things you can imagine. When I was in school and learning troubleshooting solid state sets, that was the very first thing to check after the batteries. Always kept a 100uF/ 25 volt electrolytic with miniature clip leads soldered to its terminals in the drawer.<BR>Curt<P>------------------<BR>Curt, N7AH<BR>(Connoisseur of the cold 807)<BR>QCWA# 25085 AMI# 242<BR>CW forever


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 Post subject: Zenith Royal 200 info
PostPosted: Oct Mon 03, 2005 12:39 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 794
Location: Gulf Breeze, FL USA
Hi Rickster,<BR>The primary role of the filter capacitors in an AC powered DC supply, like the ones found in most AA5 radios, is to smooth the pulsating DC produced by the rectifier into more pure DC for use as plate/screen voltage. Thats why I wondered about the need for filter caps in a battery set. I had forgotten about the secondary function of shunting all the unwanted frequencies to "ground". Thanks for the refresher.<BR>Ben<P>------------------<BR>


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 Post subject: Zenith Royal 200 info
PostPosted: Oct Tue 04, 2005 6:03 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 21
Location: BARRINGTON, ILL, USA
Hi Ben,<P>Just for your information, I found a RCA PNP germanium plug-in transistor that came out of a "junk" Zenith Royal 500D model. The Zenith number is 121-65, which was used for the oscillator. <BR>This transistor will work well as an oscillator, mixer/converter, I.F. amplifier. I also tested this transistor and it tested "Good" and had very "LOW" leakage values. <P>Here is the test results: <P>Ibco= 1 uA (microAmps)<BR>Iceo= 20 uA (microAmps)<BR>Hfe = 26 (beta gain)<P>Finally, this RCA transistor will work well as a replacement with your RCA 121-92 high leakage(Icbo) mixer/converter transistor, that you now have for your Zenith Royal 200. If you need it, I would be happy to send it to you.<P>Thanks Rickster <P>------------------<BR>


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 Post subject: Zenith Royal 200 info
PostPosted: Oct Tue 04, 2005 9:25 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 794
Location: Gulf Breeze, FL USA
GEEEEEEEZZZZZZZ! Timing is everything. Thanks for going to all that trouble, Rickster, but I ordered an NTE100 from Mouser yesterday, at $4.56 no less!<BR>Ben<P>------------------<BR>


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 Post subject: Zenith Royal 200 info
PostPosted: Oct Wed 05, 2005 12:44 am 
New Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 21
Location: BARRINGTON, ILL, USA
Hi Ben,<P>No problem, I have this RCA transistor if you ever need it. Also, you could try a little trick, before you get you NTE transistor from Mouser Electronics. Try switching any one of the (2) I.F. transistors with the defective "Leaky" mixer/converter transistor. After, you replaced all (4) of the existing electrolytics, you should be able to receive some of the Stronger RF signal radio stations. But, you will definately lose some Sensitivity and Selectivity, especially on the weaker radio RF signal stations due to have only one of the I.F. stages relly working properly. However, if this transistor is "SHORTED", instead of being just "Leaky", then you will NOT get any stations to come thru. Also, DON'T switch the oscillator transistor with the "Leaky" mixer/converter, for you will get the same results as you have now, which is No radio stations to tune in. Both of these transistors MUST have very "LOW" leakage values to operate properly. But with the I.F. stages, you could get by with "Leaky" transistors and it will still operate okay, but you will lose some of your Sensitivity and Selectivity on your weaker radio stations. The same is true with Audio drivers/output transistors, where you could get the radio to perform with "Leaky" transistors. But your AF signal will NOT be linear and you will have Audio sound distoration. <P>Thanks Rickster<P>------------------<BR>


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