Siemens rectifier E15 & C250 E150 & C30

[cathoderay57]

It is likely then that the yellow wires are the ends of the LT winding so you should see 4 to 8v AC across them with mains on. In your wiring sketch you had 2 red wires though - red positive and red negative. If one red wire goes to the transformer, where does the other one go?

[Luxman1050]

Well that was interesting the transformer got quite warm very quickly.
Anyhow yellow was getting 11.6v ac red 100v ac. Quickly turned it off because of the transformer. So yellow is the LT and red the HT.

[Luxman1050]

One red wire goes to positive c1 or 2

[cathoderay57]

I'm taking a break for some dinner so back about 7:15 P.M. Since the yellow wires prove to be the AC LT supply, then connect one yellow wire to the positive terminal of C3 and the other to the positive terminal of the 1N4001 (the end with the white bar marked on the device itself). The yellow wires can be connected either way around. The other end of the 1N4001 goes to chassis, as does the negative wire from C3. The red wire from the transformer then goes to the negative terminal of the 1N4005. Connect the positive terminal of the 1N4005 (the end with the white bar marked on the device itself) to one end of the 100 Ohm resistor and the other end of the resistor to the other red wire (which should already be connected to the positive terminal of C1. I'm a bit concerned about the transformer heating up. You'll need to make sure that the mains voltage selector is set to the right tapping (220v). If it continues to heat up it could be bad news and could mean that there is an interwinding short (possibly caused by previous storage in damp conditions).

[Luxman1050]

Okay. I thought that re transformer. Seemed fine until around 180v and upwards.
I'm bit confused so the diode with the bar/ring round the end is positive? I thought that was the negative side?

[Station X]

Originally Posted by Luxman1050

I'm bit confused so the diode with the bar/ring round the end is positive? I thought that was the negative side?

If the diode is placed in series with an AC supply from a transformer the marked end will have a positive voltage on it, that's why it's marked that way. The arrow of the diode symbol points towards the marked end.

[Luxman1050]

So the arrow end is the cathode which I thought was negative and the other end the anode the positive end or am I getting ? them the wrong way round.

[cathoderay57]

Hope this makes things clearer. Not sure what you meant by "around 180v upwards". Are you powering the mains via a variac?

[Luxman1050]

On the variac. Prior to 180v noticed nothing then once it reached 180v plus something was smelling and the transformer was getting warm. Hoping it's okay.
Thanks for the help Jerry. I'll wire that up tomorrow.

Chris

[Luxman1050]

Forgot it's set for 220V.

[cathoderay57]

I fear the transformer has had it and it won't get better on its own. Rotten luck and commiserations. However, all is not lost. I can think of 6 solutions:
1. Request a quote for rewind from members Ed Dinning or Mike Barker.
2. Message Ed with physical size, voltage and current requirements because he might have something suitable to replace it.
3. Put a wants request here on the Forum with details as per option 2 above.
4. Use a couple of miniature 9v transformers with split 230v/115v primaries wired back to back as shown in the attached pdf.
5. Purchase or build a separate 1.4v LT 90v HT external power pack wired directly into the LT and HT circuits.
6. Build a home-made HT/LT battery using non-rechargeable cells. There are several examples elsewhere on the Forum.

[Luxman1050]

I was thinking rewind. But the transformer is a nightmare to get at. I'll have a ponder.

Many thanks Chris

[Luxman1050]

Well thats the rectifier done. Just waiting on the capacitor so it can all be connected up. I've had to watch the tag strips as the speaker goes over this section and doing my best to make sure there not touching the speaker casing.
So I'll try it out despite the transformer and then if it warrants it get a rewind done.

Cheers Chris

[Luxman1050]

Well found a 470uf cap so wound her up. By 120v started smelling and transformer was getting hot. So it looks like as Jerry said a rewind or a new one. There not that easy to access on these units. But worth a go.
Oh deary me.
Cheers Chris

[Luxman1050]

Well that was not as bad a I thought removing the transformer. Picture of the culprit.

[cathoderay57]

A couple of these wired back-to-back should work - that's if you could physically fit 2 of them in the available space. Dead cheap too (I have no connection with seller) https://www.ebay.co.uk/itm/276295939747

[Luxman1050]

They are cheap. Shame mines only 50mm by 45mm so no way I'd get two in the radio not enough room.
Thanks for looking.

[Luxman1050]

I found the culprit you have a brown wire which goes to the radio's fuse. It's gone open.

[cathoderay57]

Not sure.... According to the circuit, if one of the wires to the fuse went open circuit then surely you'd get no mains to the transformer primary, which wouldn't be a reason for overheating, unless I'm missing something.... If it's a bad joint then arcing might occur which could explain the smell, but still not sure it would cause the transformer to overheat. Still, worth a punt I guess.

[Luxman1050]

It's intermittent one minute you get a reading then it goes open. So it must be shorting out. Got hot very quickly. But I know what you mean by no mains to the transformer. I'll check it again tomorrow.