RCA 98-T

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Re: RCA 98-T

Post by Bill Cahill on Thu Mar 06, 2014 6:45 pm

Do you really need to remove the push buttons? They don't pivot. They are tight fit to each shaft. Just minor cleaning, lube, and, clean band switches....
By the way, RCA used a lot of rubber wiring. It may have a lot of rotted wires, and, I suspect that includes rubber power cord.
Those little lozenge shape mica caps will also need replacing. The numbers on them are the actual pico farads. They are all five hundred volt caps.

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Re: RCA 98-T

Post by Dr. Radio on Thu Mar 06, 2014 6:54 pm

I have some ideas for you WC....

It's a lot of typing though........
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Re: RCA 98-T

Post by Wildcat445 on Fri Mar 07, 2014 12:01 am

The pushbuttons must move somehow. If they are welded to the shaft, all the pushbuttons operate at once. There is some rubber wiring, but it is in good condition so far. After I dig around performing service, who knows what will happen. I am always down for good ideas, Doc. Or even not-so-good ideas. Lets hear them. I might learn something that will help bring this thing back to life. The pushbuttons on this thing are in deplorable shape. They fall apart whenever you touch them. They absolutely must be replaced before the frau will let me bring this thing into the house. It looks to me like the pushbuttons are on a shaft with "Jesus clips" on each end of the shaft to hold it in the bezel. I may stand to be corrected if this is not correct.

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WC

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Re: RCA 98-T

Post by Guest on Fri Mar 07, 2014 12:09 am

The chassis looks very nice.

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Re: RCA 98-T

Post by Wildcat445 on Fri Mar 07, 2014 12:35 am

Thanks, MR MEZ. I'm kinda psyched to get into it. I wasn't too sure about it, until you guys got to talking about it. I thank you all for that.

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WC

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Re: RCA 98-T

Post by Bill Cahill on Fri Mar 07, 2014 11:21 am

May I see out of cabinet photos of push buttons??Front, top, bottom?

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Re: RCA 98-T

Post by Wildcat445 on Fri Mar 07, 2014 2:39 pm

Bill, in all honesty, this bezel will only stand one more removal and install before it disintegrates into dust. I am going to remove it to refinish the cabinet, and will be happy to provide some photos at that time. I really don't feel comfortable messing with it anymore than absolutely necessary. It is extremely brittle. It obviously took a dump some 30+years ago, since the original has been replaced with one off a Westinghouse radio. Thanks for your interest in this, and I will get some pics when I get it apart.

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WC

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Re: RCA 98-T

Post by Bill Cahill on Fri Mar 07, 2014 3:57 pm

The push buttons should be on the chassis. Not the bezel.

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Re: RCA 98-T

Post by Wildcat445 on Wed Apr 16, 2014 1:24 pm

The chassis in this radio appears to be more simple than it is. This radio is basically an AA5 with lots of audio. P-P 6K6's for a six inch speaker. The schematic is in Riders 10-8 thru 11 if you would care to follow along. I can't post pics on this site, so you will have to paint the picture in your mind's eye. This radio chassis is available in the table model 98-T and a console with 12" speaker, model 98K2. It is also the audio for a TV console, model THK-2 (?). This is why this little radio with a tiny speaker has all the fancy audio section. The TV chassis itself is kinda interesting, as it uses a 5V4 for the HV rectifier and a 6L6 for horizontal output and a 6V6 for vertical output. The picture of the chassis in Riders does not show the power transformer or the 5Y3 rectifier. That is on a different page than the chassis schematic. The schematic shows the radio powered by the supply in the TV chassis. If a newbie were messing with this fairly simple radio, they could be easily confused by the uncommonly (for RCA) lousy schematic. I am under the impression that this radio is from the 1940 era, give or take a couple years. That would make the TV it was used with a pre-war RCA that all the "collectors" get their shorts in a bunch over. The 6U5 eye tube currently in this set is an off-brand of some kind. It is so long that it is jammed up between the second audio tube and the tenite bezel. This has caused the bezel to crack. I have a genuine RCA 6U5 that is approx. 3/8 to 1/2 inch shorter. It will fit without pushing out on the bezel, and will allow me to put the shield back on the audio tube. There is a sticker on the rear of this radio chassis indicating that George Fathauer, the founder of AES worked on this set at some time, probably over 30 years ago. The bezel currently on this set is a Westinghouse. It is hard for me to believe that George would have allowed a hack like this to leave his shop. I need some 600 volt e-caps for this thing, since the input filter cap is rated at 475 volts, and all I have is 450. This is all preliminary, and is subject to change with further investigation. I found my foray into this set rather interesting, and felt the need to share.

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WC

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Re: RCA 98-T

Post by Wildcat445 on Wed Apr 16, 2014 5:43 pm

The schematic for this radio is also in Riders 10-97 thru 99. It is dated 1939. The TV console this radio chassis is used with is the TRK-2. My print was not very good, and I misread the model number. The TV chassis uses 1852 and 1853 tubes, two types with which I am not familiar.

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WC

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Re: RCA 98-T

Post by Bill Cahill on Thu Apr 17, 2014 11:20 am

Neat radio. Got any pics??

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Re: RCA 98-T

Post by Wildcat445 on Thu Apr 17, 2014 5:48 pm

Look on Page two of this thread, Bill. Doc was nice enough to post some pics I sent him. There are a couple of .005 @1000 volt plate by-pass caps in this thing as well. I hate it when RCA does that. I may put some 630's in there to see what happens. I hate to have to order caps specifically for this radio. I am both lazy and cheap when it comes to that. I never did understand why they used 1000 volt caps, when there is nothing close to 1000 volts in the radio. This thing should sound pretty good when I get done. It will be basically an AA5 with big audio, so it may not be a very good performer. I would have canned some of the audio and put in an RF amp if I had been doing it.

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WC

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Re: RCA 98-T

Post by Wildcat445 on Fri Apr 18, 2014 7:20 pm

I guess I will break down and order the correct caps for this thing. So far, everything else checks at least good enough to continue with the project. I put this chassis on my Variac/dimbulb tester and the 100 watt bulb got fairly bright, so the filter caps will need to be changed before I can go any farther. I only got it up to about 70 volts, before I chickened out and shut things down. The good news is the tubes light and the dial bulb works, so the PT is not dead. Everything under the hood is original as far as caps and resistors go. One tube looks like it has been changed, the 6U5 was too long, and there was a 6V6 and a 6K6 output tube. I haven't tested any of the tubes, nor have I checked the other transformers or the coils. There is a big old wasp flying in my shop, and he landed on the chassis as I worked on it. I will go back to the shop armed with some wasp killer and continue. Those nasty buggers show up every year about this time, and I have to chase them off. I'm gonna have to ask the bugman to see if there is a nest somewhere in my shop.

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WC

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Re: RCA 98-T

Post by Bill Cahill on Sat Apr 19, 2014 2:29 pm

Sorry. First time I'm been on computer in a couple of days.....
The reason was the ac component in the voltage. 630 may work fine, but, the higher the voltage, and, wattage output, the safer you are with the higher rated caps.
A lot of stuff was destroyed by using the lower voltage ones.

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Re: RCA 98-T

Post by Dr. Radio on Sun Apr 20, 2014 12:05 pm

Don't skimp on those 1000 volt'ers. Designers opted to spend the extra $ for a reason. You can get high inductive spikes in this area of the circuit, thus the need for the high ratings.

Remind me to remember to not forget to remember to gather those IF can caps for ya. Smile
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Re: RCA 98-T

Post by Wildcat445 on Sun Apr 20, 2014 12:26 pm

Wonder if Mark Oppat has 1000 volt caps for this radio? I really don't want to use Mouser or those guys. Too much trouble navigating their websites for me. I might give AES a shot. I am going out to the shop and tack in some 450 volt ecaps and see if this thing will play. I have one fried radio on my bench, just as well go for twosies. With this thing connected to my Variac/dimbulb contraption, I should be okay. All I want is a little noise. Static would be swell. Just to see. You know the drill. Why is it that only RCA has "high inductive spikes" and Philco does not? Any guesses why I try to steer clear of RCA and prefer Philco?

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WC

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Re: RCA 98-T

Post by Dr. Radio on Sun Apr 20, 2014 12:48 pm

Wildcat445 wrote:Wonder if Mark Oppat has 1000 volt caps for this radio?  I really don't want to use Mouser or those guys.  Too much trouble navigating their websites for me.  I might give AES a shot.  I am going out to the shop and tack in some 450 volt ecaps and see if this thing will play.  I have one fried radio on my bench, just as well go for twosies.  With this thing connected to my Variac/dimbulb contraption, I should be okay.  All I want is a little noise.  Static would be swell.  Just to see.  You know the drill.  Why is it that only RCA has "high inductive spikes" and Philco does not?  Any guesses why I try to steer clear of RCA and prefer Philco?

Regards

WC

WC,

It's not an RCA "thing", it's just proper engineering...Lots of radios have the HV caps in this area (as they should). Here's a good explanation:

http://www.antiqueradios.com/forums/viewtopic.php?f=5&t=238984


If you need caps, (and can wait, don't know what kind of hurry you are in?), I can send you some 1000 or 1200 volt'ers your way with the IF toppers. I'm due to make another Mouser order myself.

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Re: RCA 98-T

Post by Wildcat445 on Sun Apr 20, 2014 7:27 pm

I got it and thanks. Not all radios with power transformers use 1000 volt caps for plate bypass duty. Perhaps I have learned something that I should just routinely start doing. Using 1000volt+ caps in plate bypass and tone control circuit applications. Thanks for the information, Doc. Much appreciated, as usual.

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WC

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Re: RCA 98-T

Post by Bill Cahill on Mon Apr 21, 2014 2:28 am

And, that's exactly why many transformer radios are FRIED. He's not kidding. There is a nasty AC spike!

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Re: RCA 98-T

Post by Wildcat445 on Mon Jul 21, 2014 6:28 pm

I have gotten this little radio working finally. To get .005uf caps at 1000 volts, I wired two .01uf at 630 volts in series. I replaced the filter caps and all the paper coupling caps except two in the front end that are a pain. I have to remove the oscillator coil, and I was not in the mood to do that today. I replaced the one 6K6 and one 6V6 tube with two 6V6's, since I have lots of them. This RCA is now running on burned in (used) Magnavox 6V6's. This is a sensitive radio, and it is a pretty good performer. I am going to refinish the cabinet and the wife will hotrod the grille cloth like usual. I don't know what it looked like originally, and I don't care. I just want it to pass the frau's test for bringing it into the house. I am halfway there, since it now works.

WC

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Re: RCA 98-T

Post by Wildcat445 on Thu Jul 24, 2014 2:19 pm

This thing has some fairly serious cabinet issues.  Now I know why it was free.   Rolling Eyes 



There are some stains on the top that I can probably cheat and get by with.  There are more serious stains on the rounded corner on the RH corner.  I have no idea how you can get stains like that.  I am going to try a coat of stripper to see if that will do the trick.  It appears to be stains or residue left over from a previous refinishing attempt.  Wonder what this cabinet would look like in ebony?

The chassis is quite nice.  It still has one 6V6 and one 6K6 output tube.  I don't go to any trouble to make a chassis look nice like some guys do.  It won't work any better shined up, I figure.  I blow the dirt off, and let it go at that.



WC

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Re: RCA 98-T

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