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Old 19th Oct 2017, 7:04 pm   #21
Boater Sam
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Default Re: Problem with transformer or EZ80 - Telefunken D656W

No. Its certainly not electrolytic. Use 650v polythene or polystyrene. That's usually a yellow peril these days.

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Old 19th Oct 2017, 7:12 pm   #22
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Default Re: Problem with transformer or EZ80 - Telefunken D656W

I'm trying to find these "polythene" or "polystyrene" on e-stores but I can't find any result. It's not the same as "polyester"?
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Old 19th Oct 2017, 7:22 pm   #23
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Default Re: Problem with transformer or EZ80 - Telefunken D656W

Polyester will be fine, they are all just plastic caps of differing spec, performance and price.
For old radios providing the voltage is higher than the sets HT plus 50% the application is not arduous, top quality is unnecessary.
Any caps across output transformers need to be 1000v and any connected to the AC mains as isolation need to be X type if across the mains, or Y type if from either side of the mains to earth or accessible connections such as gram and aerial sockets.
You could use the cheap red dipped layer caps or even ceramic if you have access to somewhere to buy parts.
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Old 19th Oct 2017, 7:24 pm   #24
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Default Re: Problem with transformer or EZ80 - Telefunken D656W

Polypropylene.

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Old 19th Oct 2017, 7:29 pm   #25
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Default Re: Problem with transformer or EZ80 - Telefunken D656W

Don't worry about the exact construction of the capacitor. Any modern capacitor of the correct value and voltage rating will work. 650V is ideal, but 400V should be OK if that is all you can find. Don't go below 400V as that capacitor is critical.
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Old 19th Oct 2017, 7:58 pm   #26
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Default Re: Problem with transformer or EZ80 - Telefunken D656W

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Originally Posted by paulsherwin View Post
Don't worry about the exact construction of the capacitor. Any modern capacitor of the correct value and voltage rating will work. 650V is ideal, but 400V should be OK if that is all you can find. Don't go below 400V as that capacitor is critical.
Thanks!!! I'll try with 10nF/630V for the 0.01 uF .
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Old 19th Oct 2017, 10:36 pm   #27
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Default Re: Problem with transformer or EZ80 - Telefunken D656W

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Start with around 100 Ohms minimum, it needs to be a 7 or 10 Watt rating due to the ripple current into the reservoir capacitor (the first 50uf after the EZ80) then adjust the value to get the HT voltage back to what the sheet says it should be.
1N4007 diodes are suitable to replace the EZ80, as it is only half wave rectification, one diode will do, valve anode to diode anode, valve cathode to diode cathode which is the marked end. With the shorted valve out of course!
The connection of the diode and the resistor with the valve should be like the schematic I've done?
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Old 19th Oct 2017, 10:39 pm   #28
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Default Re: Problem with transformer or EZ80 - Telefunken D656W

That's correct.
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Old 24th Oct 2017, 2:44 pm   #29
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Default Re: Problem with transformer or EZ80 - Telefunken D656W

Hi again guys!!! So, I've replaced the 0.01 uF capacitor with a new one and I've replaced the EZ80 with the 1N4007 and the resistor in series. I've changed the fuse too (with 0.3A one cause I use 230 V AC in my country).

I have some problems now:

1) When I turn on the radio, a spark on the fuse shows but the radio is still on. If I turn off the radio and turn it on again, the fuse sometimes do the same and sometimes it blows!

2) Now, there is finally a noise from the speaker! (that I hadn't before with the EZ80). But I'm getting a small hum and nothing more (no radio station etc.)

3) I've made some measurements on the both 50uF filter capacitors. On the one (blue circle) I get 190 V DC and on the other (red circle) I get 230 V DC.
I've seen that when I start the radio, the capacitors have 250-300 volts and then the drop to 190V and the other to 230V. I've seen this react when the radio was working fine! But I can't understand. Should the one capacitor have 230 V DC? I think (with the help of the schematic) that it should have about 185 Volts. I can't see clearly the schematic...
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Old 24th Oct 2017, 3:12 pm   #30
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Default Re: Problem with transformer or EZ80 - Telefunken D656W

If its the HT fuse in the snippet, should it be 1.5A ? Can't read it well. A 0.3A mains fuse sounds a bit small, needs checking that it is correct.
You are dropping 40 v across the smoothing resistor/choke which may be a bit much.
You will get a high HT on switch on because the 1N4007 conducts immediately, the HT will fall as the valves warm up and start drawing current. That's one drawback to using a semiconductor diode instead of a valve rectifier.
You seem to have something drawing a lot of HT current, try pulling valves one at a time and seeing what happens to the HT voltage every time as you do. That may narrow it down. It could be that excess HT current is what wrecked the EZ80 in the first place.
It could be a decoupling capacitor that didn't like the high surge of HT caused by the diode and has gone very leaky as well.

Last edited by Boater Sam; 24th Oct 2017 at 3:14 pm. Reason: alteration
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Old 24th Oct 2017, 4:04 pm   #31
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Default Re: Problem with transformer or EZ80 - Telefunken D656W

Well, the fuse is 0.3A for sure as you can see on this schematic I've uploaded now. Something more I've noticed is that the capacitor I have on red circle is missing from the radio! It was missing from the first time. But it happens to have one of these. Should I put it or it doesn't help the problem?
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Old 24th Oct 2017, 6:29 pm   #32
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Default Re: Problem with transformer or EZ80 - Telefunken D656W

You say you have a capacitor to fit? But it needs to be type X and an AC voltage rating higher than the transformer output.
Thought I spotted another fuse, 1.5A, in the HT line on the other diagram snippet you posted, yes?
Still think you have excessive load on the HT.
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Old 24th Oct 2017, 6:53 pm   #33
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Default Re: Problem with transformer or EZ80 - Telefunken D656W

Yeah I have this capacitor. It's 0.022 uF and 200 VAC / 600 VDC. Should I connect it?

Another fuse? I can't find another fuse. And for sure the chassis doesn't have any other. Only the 0.3 A.
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Old 25th Oct 2017, 12:26 am   #34
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Default Re: Problem with transformer or EZ80 - Telefunken D656W

Capacitor. Connect only if you want to blow it up, its under-rated.
Sorry, thought there was a fuse but the picture is kind of fuzzy. Difficult to tell one component from another, I hate these continental diagrams.

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Old 25th Oct 2017, 9:01 am   #35
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Default Re: Problem with transformer or EZ80 - Telefunken D656W

For the capacitor across the mains transformer's secondary I would fit one that has a rating of 300 volts AC.

The voltage drop of 40 volts between the two HT electrolytic capacitors looks OK, that equates to approx. 26mA flowing through the 1.5k resistor which doesn't seem too excessive.

The HT voltage out of the rectifier seems a bit high compared to the voltage given in the schematic, you could increase the value of the rectifier's series resistor you fitted to try and reduce the voltage.

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Old 25th Oct 2017, 10:41 am   #36
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Default Re: Problem with transformer or EZ80 - Telefunken D656W

If it helps, the schaltplan for the Telefunken 654WN is very similar and uses the same valves, the voltages are slightly higher but might be OK for a ball park figure for trouble shooting your receiver, all the voltages and current measurements on that schematic are clear and can be read no problem.

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Old 25th Oct 2017, 11:12 am   #37
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Default Re: Problem with transformer or EZ80 - Telefunken D656W

Quote:
Originally Posted by electronic_93 View Post
1) When I turn on the radio, a spark on the fuse shows but the radio is still on. If I turn off the radio and turn it on again, the fuse sometimes do the same and sometimes it blows!
If the fuse sparks at the ends this points to it being loose in the holder. It may need nipping up a bit.

If I'm reading the diagram correctly this set has a gram or pickup socket. Switching the gram and touching the gram socket with a screwdriver will soon tell you if the audio stages are working. Expect a loud buzzing sound.
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Old 25th Oct 2017, 1:21 pm   #38
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Default Re: Problem with transformer or EZ80 - Telefunken D656W

Guys it is working!!!!!!!!!!!!!!! The radio is on and good!!!Bbut the fuse still sparks when I turn it on.

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Old 25th Oct 2017, 2:24 pm   #39
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Default Re: Problem with transformer or EZ80 - Telefunken D656W

Wonderful, but what did you do to get it working?
Tighten the fuse holder clips.
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Old 25th Oct 2017, 4:16 pm   #40
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Default Re: Problem with transformer or EZ80 - Telefunken D656W

I've disconnected the end of the resistor that goes on Pin 3 of the valve and reconnect it and it played!!!

Okay I will tighten and clean a little the holder clips.
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