Hi All,

I've just recapped a Kriesler 11-71 to find that the power transformer isn't working, and that was what was creating the hum, not the filter capacitors. After replacing the capacitors, one of the two front lights lit up, then a loud hum and a sharp odour. A little bit of smoke started coming out (it wasn't in the case at the time), and I traced it back to the power transformer. I left it on for another minute as the tubes were lighting up, but then a pop and some thick white liquid, almost like wax came out of the power transformer. Now I've heard this is varnish. I immediately turned it off. Well the power transformer is probably stuffed, but can I replace it? I really want to get this working, and it's my first restoration.

Thanks,
-Tim

If you need to get one and cannot find any one with a recycler.

There are organisations like Australian Vale Audio Transformers (refer Silicon Chip) and EVATCO that have them. They are not cheap.
There are some US companies that also specialise in valve radio parts.

You are going to have to add up all of the currents in all of the windings to get a new one, as it is rarely listed as to the current draw in the set.

I would also have a good look at the set to see there are no shorts. With transformers & chassis with rubber wire on them, it is always a good idea to inspect it. I have found several of these where the rubber has deteriorated to the point where a short circuit capable of destroying the transformer, was a certainty.

Marc.

Whoa, minimum $200.
Is there any chance this would fix it http://www.vintage-radio.net/forum/showthread.php?t=46198
It says that I could put the power transformer in an oven at 40 deg celcius, and that will resoak the varnish in. Or am I completely stupid. I'm low on money (I'm a student) and I brought the radio at the market because it had all the valves and everything looked in good nick, so I cant really afford to pump $200+ into it just to replace a transformer.

-Tim

That's one of the reason's for "look before you leap"! cooking a trannie is expensive.

Rule Number one....... Inspect before turning on. Plugging it in to see if it goes is a recipe for disaster. I make more money from people doing that. I have educated several people in antique dealerships locally re that also.

That sounds like a bit old wive's tale. One needs to have a look as to where it burned. It may have only fused between the mains wires and not actually damaged the windings.

If the smell was like that of burning rubber, that is likely and your comment re the white goo tends to support that to some extent. you may need to get an opinion from someone who can physically look at the thing.

Marc

Hi Marc,

I'm going to have another detailed look at the circuit tomorrow, focusing on the transformer. It actually does smell like rubber, so it may give me hope. I did check the circuit before turning it on. I recapped it and everything so it's something hidden away somewhere. I'll give it a good look at tomorrow and get back to you. If I can't find the problem should I take some photos or something, or is there someone around Melbourne that is experienced in this?

Thanks for the help,
-Tim

Being in the City you have hope of finding someone . Try the HRSA website.

There are people who advertise in their magazine, or are listed through the site, that may be worth contacting as afirst approach.

I am closer to the Vic NSW border, that is not helpful. Do take photo's, especially of the area where wires exit from the core of the transformer.

As a mateer of interest with oven drying. It is actually amazing as to what components you can wash without damage. I recently checked a transformer that had been in a flood. It was heated for some time, without any electricity of any form being applied to it.

This transformer passed all insulation tests & was put back into service.

The fault may have been on the transformer, check everything anyway? Walking away & checking it a few days later has merit.
I do that despite it annoying people who eagerly want to see it go.

With nasty non obvious ones I have a power supply. This has thermal fuses on the heater & fuses on the HT Rails.

Marcc

Here's some photos.

http://graphicgraffiti.com.au/storage/radio1.jpg
Transformer

http://graphicgraffiti.com.au/storage/radio2.jpg
http://graphicgraffiti.com.au/storage/radio3.jpg
http://graphicgraffiti.com.au/storage/radio4.jpg
http://graphicgraffiti.com.au/storage/radio5.jpg
http://graphicgraffiti.com.au/storage/radio6.jpg
Transformer (Closeup)

http://graphicgraffiti.com.au/storage/radio7.jpg
Weird Metallic Box

http://graphicgraffiti.com.au/storage/radio8.jpg
Weird Metallic Box (Closeup)

http://graphicgraffiti.com.au/storage/radio9.jpg
Tube Lineup

http://graphicgraffiti.com.au/storage/radio10.jpg
Chassis Overview

That's all well and good. But after I removed the front dials and the speaker I got to have a good look at that weird metallic box. Now the smoke had being coming from the front all along, very closeby to this box, and when the power transformer started spewing that waxy white liquid, I thought it was the transformer, but it may be this.

http://graphicgraffiti.com.au/storage/radio12.jpg
Here's a photo of the bottom of the metallic box. It's definitely burnt, but I don't know if the black stuff is plastic or what. It's got the label 'DBG96' labeled on it and a red and blue wires going in on the left, and 2 metal wires, one with some crap heatshrink tubing on it, the other without anything (just bare metal wire - could this be the short?) and the date 10 Nov 1956.

Also, I turned it on without any of the tubes in to test it. No smoke, minor minor hum. Then I put the rectifier tube in, and the transformer looked fine. I was focusing on the box at the back (the metallic burnt one) and smoke started to come out of it. Any ideas? What does this box actually do?

-Tim

Tim,

The device you have photographed is the speaker transformer. If you refer to the circuit, you will see it marked as T2 on the diagram.

The red wire goes to the cathode of the 6V4 and the blue to the plate, (or anode), of the 6AQ5. The two uninsulated wires go to the speaker as shown in the circuit.

The black 'stuff' in the case is pitch which insulates the frame from the chasis and prevents moisture ingress which would corrode the fine gauge wire used in the transformer.

Possible causes for the speaker tranny to overheat are a short between the winding and the case,(Unsual but does happen), C16 is shorted out, or there is an internal short in the 6AQ5. If the transformer didn't smpke when the 6AQ5 was removed, I would suspect that is the culprit.

BTW Underneath the cahssis there are many points at mains voltage so pull the mains plug out when working on the set and only have it running when taking measurements.

Cheers, Graham...

OK now thats a different animal. Thats the speaker transformer.

Its what is called an ISO type. The black stuff is pitch.

The two coarse wires are the ones that go to the speaker.

The other two are on the HT & Plate of the output tube.

There are a few possibilitys as to why it would smoke.

(Note most electrical stuff runs on smoke: If the smoke gets out, its often stuffed)

It's shorted inside ...The frame of the transformer is live and should not contact the outside. Remove the wires & check with ohm meter.
B+ should be low. (not a good idea to turn it on to test that, without looking at everything else first)

The output valve is shorting on the plate side or within.

The plate bypass capacitor is shorted this would mean no B+, as it would drag it down.

You left a solder dag or a bit of wire there and its shorting to ground.

Its got the wrong valve in there.

You put the plate wire on a ground terminal.

If its 6V6 plate is pin 3 screen is pin 4 if is 6M5 its pin 7 Screen pin 1......often the second wire is on the screen pin. If its another valve let me know what it is.

That should keep you busy for five minutes

Marc

Well the speaker transformer looks alright within, the pitch has melted a bit, but I guess that's normal for a 50+ year old radio.

I'm going to test plugging it in without the 6AQ5 valve. Should I have all the valves in but not that one, just the rectifier, or none at all?

The capacitors are brand new, so they shouldn't be shorted. I have got a multimeter, but I'm not too good at using it. It's really a learning experience. I'm a student, and I've only built some headphone amps.

If the valve is shorted, does it show any physical signs? Can I get one locally or do I buy one online off a tube store?

As I said, I'm crap with a multimeter, so you may need to guide me through it. Sorry.

-Tim

Alright, I tested it with only the rectifier, and it smoked a little bit, not much though. There was a hum present, and a slight crackle noise. With no tubes in at all, nothing happened, not even a hum. With all tubes in, there was smoke, a loud hum and some crackle. With 6AQ5 out, and the rest of the tubes in, it was about the same, so I don't think the valve is shorted because it lit up as well.

One thing that did happen again was liquid coming out of the power transformer. After I unplugged it, and left it for 5 minutes, the transformer's casing was still hot to the touch. I haven't tested the transformer yet with the multimeter (because I'm not really sure what to do and don't want to kill myself) so I'm stalled. Any ideas?

Thanks,
-Tim

The reason that I suggested not turning it on before checking was because I am convinced it has a short. I am not surprised that the transformer is getting hot.

Heavy growling is a dead set giveaway that there is a short and continuing to run it that way will cook the tranny.

If you ran the set and it crackled with the valves out then forget them. The heavier crackle was the increased load. Pin 5 should be plate & 6 the screen on 6AQ5 and its a 7 pin. Having no speaker load can cause a flashover there in some amps. Do not turn it on & look.

Take a picture of the inside of the pan in that area. I note the bolt out of that speaker transformer sticking up? Lift the transformer & make sure the plate wire is not cut on the edge, or crushed by the edge of the can.

If there is sufficient melt the core may have moved down and is in contact with the chassis. can't really tell if there is metal under there from the photo.

The fact that the heaters glow is not relavant at this point.

Marc

Alright, so there is a short somewhere. Here's some pictures of under the chassis. I've left them in high resolution so you can zoom in on them if you want.

http://graphicgraffiti.com.au/storage/radio13.jpg
http://graphicgraffiti.com.au/storage/radio14.jpg
http://graphicgraffiti.com.au/storage/radio15.jpg
http://graphicgraffiti.com.au/storage/radio16.jpg
http://graphicgraffiti.com.au/storage/radio17.jpg
http://graphicgraffiti.com.au/storage/radio18.jpg
http://graphicgraffiti.com.au/storage/radio19.jpg
http://graphicgraffiti.com.au/storage/radio20.jpg
http://graphicgraffiti.com.au/storage/radio21.jpg
http://graphicgraffiti.com.au/storage/radio22.jpg
http://graphicgraffiti.com.au/storage/radio23.jpg
http://graphicgraffiti.com.au/storage/radio24.jpg
http://graphicgraffiti.com.au/storage/radio25.jpg

Is it possible dust can transfer electricity causing a short, or should I resolder all the solder points or what? The yellow poly-caps were replaced by myself a few days ago, as were the electrolytics.

Thanks,
-Tim

I just stumbled upon something very interesting that may explain where the smoke has been coming from. Under one of the big carbon resistors I found some burnt cable insulation, and that cable comes from the speaker transformer, finishing up at the 'tone' potentiometer where is joins up with the cable coming off the speaker. Here's a photo.

http://graphicgraffiti.com.au/storage/radio26.jpg

-Tim

In most cases the tone control in series with a capacitor which comes off of the plate of the output valve. if they have chosen to take a live wire across & some one has managed to burn it through with a soldering iron that will cause a problem if it can ground.

You can disconnect the speaker transformer wire that is going to HT..not the plate and check with an ohm meter, between plate & ground it should be infinity ( no conduction).

Marc