I do make a point of insulation testing, transformers even that an RCD will trip here if it is really bad primary to an earthed frame.

I do not consider 34 degrees hot after that time. Think what it will be on a 40 degree day? If the smoke has not escaped after 3hours, I suspect it won't. And the biggest danger is from dud components.

One of the reasons the old radio transformers are so big, is their "rating". A transformer designed to run 24/7 will be larger than one designed to run a few hours. That's why some of those piddling small wall wart, plug transformers die quickly.

Do note that Altronics sell an Insulation Tester (I have the older version) that has switched voltage; 100; 250; 500; 1000V. If you play with a lot of valve radios, it is quite useful for leakage testing non polarised caps, at close to their rated voltage, or B+ voltage, which is after all, the voltage where you need to know.

The circuit has voltage & current for B+ +/- 20% is normal. The set is back biased so the voltage of 13V across R12 will only be correct if the current draw is correct.

Do note that that is not consistent with their quote of 40mA, to get 13V that it's 48mA? -12.5V 250VPlate 6AQ5 draws 45mA. so 10.8 V across R12 may be more likely. Make sure it is on 240V tap. Its a shielded transformer, so a good idea to mains earth.

Make sure R11 & R13 are ok as those have an attrition rate.

Marc

Marc

The scheme is here:-

http://www.kevinchant.com/11--series.html.

I am considering to get a megger, just haven't make up my mind which one to get.

Thanks Marc, I will check the voltages tonight when I get home.

Aside from radio & other distractions I do tag & test (Handy when you fix commercially) so can justify such a device albeit I have saved several bits of test equipment, that is also able to HV test caps.

As said, the Altronics one is the one I saw as most useful as a stand alone Megger / Insulation tester, was the Altronics one. The current equivalent to mine is Q1242A. 100V; 250V; 500V & 1000V Direct current. (Note "Megger" is a brand)

Do note that these are not for big motor start caps and do not test capacity. They will however test high ohm resistors.

Marc

Thanks Marc.

An update for my radio. I borrowed a Power Mate power and did some testing with it.

My only other valve radio is a Fleetwood 1003 and it has 4 valves 6AN7, 6N8, 6M5 and 6V4.

It consumes 28 to 30 watts according to the meter.

The Kriesler 11-81 consumes 33 to 35 watts. This is with all the 5 valves and 2 lamps.

The valves are 6AN7A, 6N8, 6DB7, 6AQ5 and 6V4.

The temperature raised from 22C to 49C in an hour and to 54C in 2 hours time.

When all the valves and lamps are removed, the radio consumes 3.1 watts.

For what it worth, I did the neon lamp test mentioned above and the transformer passed.

All else I can do is get a merger and do the insulation test. I will do that when I get one.

I hope this may be useful for others as some kind of reference.

If anyone has a radio of the same model and read this, hope you can tell me the temperature of the transformer in your radio after an hours use.

See what your Fleetwood consumes without the tubes and dial lights. Should be around what the Kriesler transformer does. I have a couple of Aussie radios here in the USA, we do have 240V (as a pair of 120V feeds 180 degrees out of phase) but at 60Hz, which makes for cooler operation of 50Hz transformers.

I think your Kriesler transformer is likely okay, based on what you wrote above.

I am not at this point seeing an issue with the transformer. If it was shorted I would expect smoke after a long period and if you have a fuse box with RCDs, or a stand alone one, It would trip with the transformer body & shield earthed, should the primary leakage be excessive.

The internal shield of the transformer will bleed charge to the chassis which is why one fits an earthed lead.

Thanks guys.

Just an update.

I tested as suggested by Wa2ise and the Fleetwood 1003 consumes 3 watts without valves and the lamp. So it is really close to the Krisler. However, the temperature rise is much smaller. It rises from 23C to 26C in an hour.

I then tested the Fleetwood with all valves and the lamp. In an hour the temperature rises from 23C to 42C.

This puzzled me then I realise it maybe has something to do with the size difference between the two transformer.

The one in the Fleetwood is 8.4x7x3 cm,
The one in the Kriesler is 7.5x6.5x3.1cm.

The Fleetwood is larger.

Another observation is the RMS current draw difference without load.

The Fleetwood draws 0.033A, the Kriesler draws 0.052A.

So I guess the Kriesler one is designed to run hotter.

Any ideas?

Yet another difference is the Kriesler one doesn't contact the chassis as much as the Fleetwood one. One side of the Fleetwood transformer is in contact with the chassis. The Kriesler one is raised by four washers above the chassis.

Just for comparison, a Logitech iPod dock has a transformer rated as 6.5v x 2. 2.4A.

It consumes 3.0 watts without load. The RMS current draw is 0.09A.

It hums too.

The Kriesler transformer sounds fine to me. 53-55 degrees is not that hot for a transformer.
The lower current draw as well as the heatsinking effect of the chassis would explain why the Fleetwood is running cooler.

Nothing to worry about!

Anyone can explain a bit to me about why the RMS current draws are so different but power consumption is similar?

0.033 vs .0052 vs 0.09 A

What must be understood is the distribution of the energy between AC wave & DC.

240VAC RMS is a practical figure that is based on heating. The RMS Voltage corresponds to the amount of energy required to heat a set resistance to the same degree as 240V DC.

An AC waveform peak of around 380V is needed to achieve the same heat as 240V DC. When you rectify AC you get the peak voltage, not the RMS. So it will appear different when compared. Trigonometry also gets involved in AC.

Eg When adding voltages in the windings of you car alternator (3 Phase) that is a vector sum. So in a 240V 3 phase transformer 240 + 240 = around 415V (Messy stuff)

Marc

It depends on a few things. Firstly, RMS refers to the root-mean-squared of the voltage rather than the current.

The next thing is that the voltage may be different in each location a member tested a transformer in. 240v is merely an unofficial nominal mains voltage. (The official is 230volts these days, dictated by a fairly worthless AS 60038 invoked by idiots who have nothing better to do with their time than created politically correct rubbish that doesn't become reflected in practice.)

<rant>

Whilst we all call the mains voltage 240v, it can be as low as 228 volts or as high as 252 volts and still be considered acceptable and within tolerances. When AS 60038 replaced AS 2926 the nominal voltage was lowered but the upper tolerance range was raised, which meant that supply authorities did not have to adjust dozens of generating stations and tens of thousands of local substations making the whole exercise of "standardisation", as the pollies called it, worthless as mentioned before, as what we get out of the power point is the same as what came out of it in 1999.

</rant>

That said, when calculating power in an AC circuit, a difference between two voltages or two flows of current in as many tests can mean a lot. Then because the circuit (in these cases) is inductive, there is impedance, inductive reactance and power factor to consider. I've forgotten most of this as I learned it all 24 years ago when I was doing my trade and never dealt with most of the mathematical formulas in practice. But they are all there and have to be taken into account.

I agree with Marc regarding the transformer. After giving it some careful thought and based on previous experience with them, transformers don't die hard - if it has a serious issue it'll probably have smoked out by now and in an enclosed space and being next to five hot valves there is every reason for it to get to 50°C. The testing done so far was still worthwhile though. It pays to be sure. An old habit of mine years ago was to leave the radio on my bedside table on through the night as I found it easier to get to sleep with music on. I don't do that anymore because one night the transformer in that radio flamed out and smoke filled the room - I woke to an almighty stench of bubbling transformer varnish and was very lucky that I did wake up at all. Death by poisoning is much easier and quicker when a victim is asleep because breathing is much lighter and the senses of taste and smell are not as acute.

It can sometimes pay to have a second or even third opinion and because of the above experience, I never consider that too much can be done to make sure something is safe to operate. Your radio should be okay all things considered.

Thanks Brad, Marc and TV Collector.

It is great to know that my transformer is ok.

How long a valve radio is designed to work continuously when it is new?

4 hours? 8 hours?