Radio ID: Bit off more than I can chew.

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Radio ID: Bit off more than I can chew.

Post by NashvilleRad on Sun Sep 02, 2012 8:42 am

I came across this radio yesterday in an East Nashville discount store ... I had to buy it (it was next to nothing, as always).



The model number is RCA 5QR73FM, which I've come to understand a couple things:

* It's a german-made model for RCA (?); and,
* It's another deal where I can't find much about it, especially schematic-wise.

The buttons, switches, knobs, pots, vari-cap, etc - all in fantastic condition. The inside though - I probably bit off more than I can chew - not even sure of what the tube lineup is supposed to be. Looks like the billet is missing out of the hole in the front.

Any help would be appreciated.

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Re: Radio ID: Bit off more than I can chew.

Post by willy3486 on Sun Sep 02, 2012 11:47 am

It looks like a Grundig or a Graetz made radio of the 50s maybe. I winder if RCA had those companies to make some of the radios and label them RCA. IF so a look for Grundig or Graetz on the web might turn up a model they made under their names. And if so that model could be searched for schematics. If you find a grundig or Graetz model post it, someone here might have some info on one of those models.

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Re: Radio ID: Bit off more than I can chew.

Post by Ken g on Mon Sep 03, 2012 11:51 pm

Plug it in & see if it works . Every one of those i have had worked to some extent and worked good after some usuall cleaning of switches . A coupe needed some capacitors .

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Re: Radio ID: Bit off more than I can chew.

Post by Resistance is Futile on Tue Sep 04, 2012 12:13 am

I would suggest replacing the Caps first then plug in and see if it plays.
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Re: Radio ID: Bit off more than I can chew.

Post by NashvilleRad on Tue Sep 04, 2012 7:27 am

Well, I haven't even cracked it open yet - not even sure if all the tubes are in place, and, haven't really looked under the chassis to see the condition of the caps.

All my test gear is packed for moving, so it may just have to be an eyes-on inspection to see anything obvious ... still looking for a schematic though in the meantime.

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Re: Radio ID: Bit off more than I can chew.

Post by Doug Burskey on Tue Sep 04, 2012 10:33 am

I have seen German built RCA sets before.

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Re: Radio ID: Bit off more than I can chew.

Post by repairtech on Tue Sep 04, 2012 2:17 pm

Those German sets are pretty much all the same deal.
Complex circuitry and multiple layers of under-chassis components to fish through.

The pretty much all need a re-work of the power supply and some inter-stage capacitors, along with cleaning and lubing of the tuning mechanisms.

Have fun.

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Re: Radio ID: Bit off more than I can chew.

Post by chrisc on Wed Sep 05, 2012 6:34 pm

It seems a lot of these ' RCA's ' were made by Graetz although it is not 100% clear and I don't see that exact model. These German sets are somewhat harder to work on but the flip side is that they were usually well made with high quality components and tend to be great performers when done. Looks like the eye tube may be missing - those can run into serious money .

I think you'll find there is a clutch mechanism inside that moves only the AM or FM tuning needle depending on what band you select. That can easily get jammed up.

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Re: Radio ID: Bit off more than I can chew.

Post by NashvilleRad on Mon Sep 10, 2012 7:29 am

Thanks for the replies ... I did have a minute to check it out and verify the tube lineup - nothing powers on - no tubes glowing either. I did at least check the cord and verify power was getting to the transformer. Other than that, the chassis will have to come out for any other checks - tight quarters.

The eye tube was hanging on a wire inside the radio. It's parallel off the heater supply with the panel light - and of course, the panel light itself is missing.

Also, a previous owner apparently tried some strange speaker modification with stereo jacks and unwired gang switch on the back cardboard panel. That will come out eventually.

The closest, similar model I can find is the Graetz Comedia 4R-3366, which you can see on the paid-for antique site (I'm not a member).

The photos there look nearly the same as best as I can see, and the tube lineup is the same - the speaker is missing out of the bottom though - presumably removed to feed the strange external speaker mod.


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Re: Radio ID: Bit off more than I can chew.

Post by chrisc on Mon Sep 10, 2012 3:13 pm

There will almost certainly be a fuse inside and if that has popped then of course you would have no power for anything. You will need a schematic to make headway once you get inside - the wiring is usually convoluted and hard to trace but its only the same concept as American radios - replace the caps and so on. Definitely swap out the electrolytic caps. I've only done 2 German sets but they were not really hard - just took twice as long as I played 'hunt the circuit' ! Be careful with that twirling ferrite antenna as they are fragile.

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Re: Radio ID: Bit off more than I can chew.

Post by NashvilleRad on Mon Sep 10, 2012 3:41 pm

Yep - that was my first goal after getting the chassis out - find that fuse and check the primary and secondary. All of the pushbuttons and knobs/dial are in excellent condition and work smoothly.

I found a copy of another Graetz 4R model schematic - very, very similar - same transformer and tube lineup and physical arrangement - probably not too far off.

Since everybody likes pictures ....

Here's a photo of some sort of presumed high-fidelity mod for an external output


Horrible picture - the original speaker wiring has been cut and the speakers wired to the weird mod.


Output mod jacks and gang switch sticking out of the cardboard grill (I already removed these to get the spiderweb of mod wiring out of the way).


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Re: Radio ID: Bit off more than I can chew.

Post by chrisc on Mon Sep 10, 2012 6:49 pm

Well it doesn't look too bad - The fuse must be inside that selector switch thing on the transformer. That's what the note is referring to, in French and German. That's a strange-looking tweeter mod to be sure but I'd say you are in business as long as the 'iron and copper' all checks out, (which with any luck it will do, as it is all protected by the fuse).

I can't see the audio transformer - is it there ?

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Re: Radio ID: Bit off more than I can chew.

Post by NashvilleRad on Tue Sep 11, 2012 6:44 am

I think you're correct - I don't see an external fuse anywhere ... and ... the schematic I have spells out those rating selections exactly. I'll take a closer look.

The output transformer is sticking sideways out of the chassis in the bottom right of the middle picture behind the can cap and cut wire.

I think (I'm hoping) 95% of this is getting the power restored; 4% geting the speakers wired back correctly; 1% caps/resistors/miscellaneous.

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Re: Radio ID: Bit off more than I can chew.

Post by simplex1040 on Tue Sep 11, 2012 10:15 am

That wierd mod is a crossover network someone added
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Re: Radio ID: Bit off more than I can chew.

Post by NashvilleRad on Tue Sep 11, 2012 10:51 am

Well, here's the fuse.



It took me a few minutes, but when you rotate the input voltage selector knob all the way counter-clockwise, there is a final detent position that exposes the small fuse holder.

And yes ... the fuse holder is spring-loaded, so after some careful searching, I found it. I'm presuming it was already blown before it launched, and the ends are corroded as well. So, according to the cardboard back grille, I need at least a 0.7 amp replacement for 110-127 VAC.

simplex1040 ... I have a recently-removed crossover network available if anyone needs it - built on a Radio Shack board Very Happy

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Re: Radio ID: Bit off more than I can chew.

Post by chrisc on Tue Sep 11, 2012 6:24 pm

I'd suggest replacing the main electrolytics, checking the tubes at least for shorts or open filaments and then gently ramping it up using a Variac whilst watching the current like a hawk. With a little bit of luck it'll power right up. You will still need to replace the other caps to get it to work 100% but you might find your resistors are OK. Suggest you keep the negative lead from the lytics as short as possible or you might spend 2 weeks looking for a hum like I did Sad

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Re: Radio ID: Bit off more than I can chew.

Post by NashvilleRad on Wed Sep 12, 2012 8:09 pm

I haven't been able to get back to the radio - I had to take a trip to Denver for work ... which means ... I made my homage trip to Fistell's, and even the closest rated fuse they had that size was 0.8 amps (0.7 required), so I grabbed a 5-pack. Close enough.

I haven't been able to take the chassis out yet - and of course I'm going on a schematic that's as close an analog I can find, so the component inspection/measurement hasn't been done.

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Re: Radio ID: Bit off more than I can chew.

Post by NashvilleRad on Fri Sep 14, 2012 5:12 pm

Check it out ... glowing tubes and FM is loud and clear.



Not really able to tune anything in on AM and LW, but I just got started.

chrisc - I had to make and use a dim bulb tester for power up - I'm moving and my Variac is packed up.

The 'magic eye' tube appears to be OOC, plus, only the heater voltage lines are wired to the socket.

I had to replace part of a wire run that was cracked (and open). I'll start going through caps next.

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Re: Radio ID: Bit off more than I can chew.

Post by chrisc on Sat Sep 15, 2012 1:22 pm

Great stuff - as least you know the 'foundations' are solid. Trust me, those big electrolytics will quit on you unless replaced. What they will actually do is work beautifully until you lovingly re-assemble and polish up the radio and then quit ! AM should in theory be easier than FM so hopefully there is not much amiss there. Maybe the band switches need a clean - up ?

You wont hear much more than the occasional navigation beacon on LW anyway (unless you're moving to Europe !).

Does your FM go up to 108 MHz or stop at 100 MHz ? I'm thinking your set might have been intended for the European market.

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Re: Radio ID: Bit off more than I can chew.

Post by NashvilleRad on Sat Sep 15, 2012 2:41 pm

I'm definitely going to get to the electrolytics - I haven't taken a chance to inventory them. I've been working on determining where the magic eye tube + and ground leads tie in - I think I figured that out.

The radio does top out at 100 MHz.

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Re: Radio ID: Bit off more than I can chew.

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