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Old 2nd Dec 2020, 2:47 pm   #1
marty-radiogram
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Default EKCO SRG 601. transformer

Morning all
initially when i bought it it wasn’t working at all, there were 2 blown resistors r60 & r61 which i think were 2k Ohm and a big Capacitor which was looking suspect [the top was convex] the cap
was 3000 uF 30V i swapped it for a 3000 uF 40 volt one. and the machine came to life and was ok
for a few days , everything working , turner and deck.

Then i decided to put it all back in the cabinet properly , cable tying the cap to the chassis
[this could have been a mistake] as its not worked since.

the transformer is getting too hot , there is 4.6 apron on the rectifier wires when unsoldered, and the illumination bulbs are just glowing the filaments

suspect I've wrecked the transformer , does anyone know the spec and where i could get one ?

best regards Martin

Last edited by Cobaltblue; 2nd Dec 2020 at 3:27 pm. Reason: Corrected Name
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Old 2nd Dec 2020, 6:13 pm   #2
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Default Re: EKCO SRG 601. transformer

Are you sure you just havent shorted one of the tags of the capacitor to the chassis when cable tying it? try it with it disconnected again.
Steve.
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Old 2nd Dec 2020, 6:50 pm   #3
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Default Re: EKCO SRG 601. transformer

The voltage on TR10 collector should be 22v so it looks like the transformer is going to be about 15v secondary, but there is a tap on the secondary winding for the dial bulbs.
Can you check to see what voltage is marked on the dial bulbs..
I take it the 3000uf cap was C65 (trader refs.)
You might want to check the DC blocking electrolytic caps C81 as well.

Mike
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Old 2nd Dec 2020, 7:34 pm   #4
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Default Re: EKCO SRG 601. transformer

The dial bulbs are 6.3v 0.3A. Three bulbs so 6.3v at 1amp for that winding, a little more would be good say 6.3 at 1.25A.
Cable tying the capacitor to chassis put a short circuit on the 22v line and overloaded the transformer and the bridge rectifier. The + side of the cap is tied to chassis the can is floating on the 22v neg line.

Whether they are now faulty you can test by removing the short, you may be lucky.
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Old 3rd Dec 2020, 12:07 pm   #5
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Default Re: EKCO SRG 601. transformer

Morning ,
and thanks for the help, i have removed the capacitor completely ,and the situation is the same 1,4 volts or so on the dial bulbs [just glowing the filaments] so i guess i have wrecked the transformer. Would the rectifier be likely to be ruined too ?
I ask because I am a mechanical engineer with a little bit of electrical knowledge, but not enough to fix this , without some help. Is there any way i can test the rectifier , i have a Fluke meter , and an analogue AVO. Also assuming the transformer is scrap are there such things available these days ? Thanks in advance Martin
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Old 3rd Dec 2020, 12:28 pm   #6
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Default Re: EKCO SRG 601. transformer

The transformer could possibly be rewound, a couple of forum members do transformer rewinds, put a post in the wanted section.

The rectifier has been severely overloaded so I would replace it.
The rectifier appears to be a selenium bridge, post a photo. If it’s selenium 4 silicon diodes and series resistor will replace it, if it’s a silicon bridge just 4 diodes will do the job. There are silicon bridge rectifiers available which could also be used, again with or without the series resistor.
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Old 3rd Dec 2020, 12:39 pm   #7
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Default Re: EKCO SRG 601. transformer

It's a bridge rectifier. Type LT119 30V 2A.

Before writing off the transformer I'd remove the rectifier and check the AC voltages on the secondary winding of the mains transformer.
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Old 3rd Dec 2020, 1:30 pm   #8
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Default Re: EKCO SRG 601. transformer

In post #1 Martin said he measured the voltage with the rectifier disconnected.
I have already had some discussion with Martin via the Radio Museum and did ask him to remove the pink wires from the rectifier.

Mike
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Old 3rd Dec 2020, 2:16 pm   #9
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Default Re: EKCO SRG 601. transformer

Sorry I was mislead by post #5 which spoke of removing the capacitors. Little point in doing this if the wires had been disconnected from the rectifier.
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Old 3rd Dec 2020, 5:00 pm   #10
marty-radiogram
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Default Re: EKCO SRG 601. transformer

here are a couple of photos of the rectifier, if anyone is able to identify it ?

could i buy a transformer from someone like radio spares , do you think ?
I mean I have no clue what type it is, is it just an isolating 1:1 with some low
voltage tappings for the dial bulbs , or is there more to it ??
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Old 3rd Dec 2020, 6:10 pm   #11
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Default Re: EKCO SRG 601. transformer

There is more to it, you need voltage for the dial bulbs and about a 15v secondary winding for the radiogram tuner amp., its not 1:1, that would just write off the whole unit if you did that.
The rectifier is a selenium one so a silicon bridge will work fine but may need an additional resistor to keep the output voltage the same as the selenium type.
There may well be other transformers from RS that would work, not in a position to check.
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Old 4th Dec 2020, 1:21 pm   #12
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Default Re: EKCO SRG 601. transformer

Next question, does anyone think this RS transformer will do the job?

RS Stock No.:504-773

https://uk.rs-online.com/web/p/chass...d%22%3Atrue%7D

it seems to me that it might , but hey.
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Old 4th Dec 2020, 8:08 pm   #13
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Default Re: EKCO SRG 601. transformer

No, you need a larger VA rating than that. Try https://uk.rs-online.com/web/p/chass...rmers/0504587/
Both secondaries connected in parallel.
Check the dimensions against your one, if they are about the same or very slightly larger then it should do.
You will need to do something with the dial bulbs.
Maybe get 3 x 6.3v 300mA bulbs and wire them in series, and also run them on the 15 volt supply. They will all need to be identical to run them in series.
Can someone else confirm this.
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Mike

Last edited by crackle; 4th Dec 2020 at 8:18 pm.
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Old 4th Dec 2020, 8:46 pm   #14
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Default Re: EKCO SRG 601. transformer

The bulbs in series should work fine, but you will need isolated bulb holders to be able to do this.

Ed
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Old 4th Dec 2020, 11:34 pm   #15
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Default Re: EKCO SRG 601. transformer

Just noticed the lamps are not all the same current so series would cause other problems. I still think a rewind is the better option if that’s possible.
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Old 5th Dec 2020, 10:49 am   #16
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Default Re: EKCO SRG 601. transformer

The lamps could be changed to all 300mA.
But a rewind would keep everything more original.
You could send a PM to Ed Dinning.
By the way it is noted in the service manual that you must not use speakers of less than 12 ohms.
Mike
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Old 6th Dec 2020, 11:56 am   #17
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Default Re: EKCO SRG 601. transformer

Morning , Just to begin with to get the tuner amp in a state of function.
if i bought the Transformer Mike suggests [which I will] .

Before i drive to RS is there any way I can test the rectifier ? i have a Fluke meter and an old AVO

then assuming its Kaput too and I get a bridge rectifier , do I need an additional resistor in the system somewhere too?

thanks Martin
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Old 6th Dec 2020, 11:53 pm   #18
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Default Re: EKCO SRG 601. transformer

These types of rectifier are not easy to test with a meter, it is easier to connect it up and see. But you could buy a new rectifier anyway just in case. A 4 amp bridge rectifier only costs a couple of quid. https://uk.rs-online.com/web/p/bridg...fiers/6296437/

Mike
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Old 13th Dec 2020, 2:50 pm   #19
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Default Re: EKCO SRG 601. transformer

Morning Helpers,
Update , I have changed the transformer for the one Mike suggested together with the rectifier , put a new capacitor in and insulated it from the chassis.
So thus far the tuner has come to life which is Fab, but the RH channel is quiet compared to the left.
Now winding the clock back to the beginning of my saga , R60 & 61 were blown, I swapped them for 2.2k ohm ,

But should they be just 2.2 ohm , i can't tell from my circuit diagram , as its too small to make out.Help please.

also as an aside if all this works , i am thinking of running the lights off a separate
transformer at 6,3 V
many thanks Martin
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Old 13th Dec 2020, 3:14 pm   #20
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Default Re: EKCO SRG 601. transformer

The Trader Sheet clearly shows R60 and R61 as being 2.2 Ohms.
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