I know Marc, I suggested a heavier wattage for the first HT dropper resistor where there will be ripple current added. NOT the 100 ohm back bias.

2.2nF 2kV caps cannot be bought at Jaycar, hence my suggestion. The correct type CAN be hard to get.

I search for components in my day job as a design engineer, where I design high-reliability products that are expected to run continuously for up to 20 years.

One tends to look at current squared by resistance. That's where things were going, some times heavying up resistor Wattages can have nasty consequence's. Especially when there is a loading fault.

Marc

Marc, all I can say is to repeat the last line in my response.

The point I would make from fixing stuff for nearly six decades is that we are not dealing with stuff designed to last. In the wasteful word much is not designed to last.

As a matter of principle we cannot in the name of originality change too much. However, there are occasions, like in the fifties series on Nippers a parallel pairing of 22K resistors became 10K and a large number failed when maximum current was achieved, as they were overloaded.

By introducing bigger wattages, we run the risk of causing something else to have a catastrophic failure in a fault situation, a situation common in old radios. My point is that with back bias, which is often part of long unreliable tubular resistances and dropping resistors. One needs to appreciate the ramifications of the action.

That is why I point out that resistances like back bias are best left to burn on fault, in preference to sustaining the fault current and destroying the rectifier or transformer and I have seen plenty of that expensive scenario.

Digressing it is interesting to see the weird external things that can cause issues. Last night yet another frog met the swampy air conditioner fan? Despite blocking all paths in from the outside (wall type). That jammed the fan (common): On switching off a few seconds later the spike trips on the computers contactor box activated and suddenly the computer was running on UPS: Nothing else got tripped. Aircon is on a different circuit.

Marc, most readers of this site would have no idea what a "swampy" is!

For the coastal dwellers among us, a swampy is an evaporative air conditioner, which won't work effectively unless the relative humidity is very low.They consist of a fibre-like material onto which is run water and a big fan.

I also don't know what is meant by "One tends to look at current squared by resistance."

Marc maybe I should explain why I suggested substituting a 5 watt resistor in the R30 position.

If you work out the total current draw of the unit (using the 6M5 data sheets and the voltages shown on the circuit) you get just on 100mA.
Given R30 is 220 ohms, that results in a voltage drop of 22 volts and hence a dissipation of 2.2 watts.

So we are already over the rating of a 2 watt resistor - someone at Kriesler did not do their sums!

But there is another problem. As C32 ages, its ESR increases. That superimposes an extra voltage drop across R30.

Now it takes some complex maths (integral calculus) to work out the precise area under the curve, but using some gross simplification, typically, depending on the state of C32 and assuming a healthy 6V4, one could reasonably expect to see an RMS ripple voltage of 10 volts RMS added to the DC voltage of 22 volts. In this case the dissipation increases to 3.2 watts.

No wonder that 2 watt resistor cooked!

So I hope you now understand why I suggested a readily-available next size up 5 watt resistor.

Regarding protecting old gear from damage (and avoiding fires in wax or bitumen impregnated mains transformers) I believe in fitting a thermal fuse, insulated in silicon rubber tubing and connected in series with the mains. These sleeved fuses are then attached in contact with the outside of the transformer winding using a method that best suits the transformer.

A normal fuse of a rating large enough to handle inrush currents reliably will usually not fail with a 2X fault overload condition - leaving the transformer in such cases to slowly cook and let out its smoke.

Remember you cannot solder to these fuses, you need to use crimp connectors.

The transformer specification, which I have a copy of as far back as 1937 said that on fault nothing in it should support combustion. The older caps were duds after a draw 0f 10mA and that was allowed for. Some of what the Americans call "wall warts", which are the small conventional transformers that plug into a wall socket, have fuses in them, which means that if is opens, you toss it away & get a new one,

I would agree on the uselessness of fuses in many early radios & TV's. I did post a photo of a Thorn's transformer that melted down the secondary. As there was no earth leakage primary side and it was under 5A. Nothing tripped out. Had the owner not seen the smoke it had the potential to raze the house.

I did have a repair set recently with two seriously upset dropping resistors. Don't know what happened there but the circuit showed three? No wonder the voltage was low.

I did have a UPS that dropped a cell in a battery and I was lucky with it. I just happened to see it display showing the battery percent falling for no apparent reason. The battery boiled & bulged. totally inadequate protection. Needed a thermal fuse, or a PTC.

One thing to consider when replacing chokes with dropping resistors, in particular, is the use of panel mount resistors as that gives a greater heatsinking area.

Now, swampy is a common terminology that been around for decades in reference to common evaporative air conditioner. The text said it was an aircon and the fact it has a wet sump or froggy swimming pool, that, makes it very attractive to Kermit & friends. For an Aircon designed for Australia its yet another design fail.

You have only to start fixing radios to see what strange thing happen & go awry.

Hey all,
Well R 25 and R30 are both high. With R30 nearly double what it's supposed to be.
I am replacing like for like. I am not a fan of changing specs as I have forgotten all that stuff from way back when I fixed everything from 1950s valve based nav systems to missile systems with the RAAF.
All the paper caps will go. I did replace a couple of valves when I first got it as well.
Wait and see

Bad caps can kill valves. It is amazing to some how well the majority of radios work, when you bring them as close as possible to their original specs.

My cartridge is a BSR C1, but I can't find any. The one Ian suggested has a metal clip in base where as this one has two plastic clips at the front and back.
Any suggestions?
Thanks

You can also get the BSR cart from WES.

Re the 220 ohm resistor, for the reasons I've stated, Kriesler clearly made a mistake when they specified it. You should never stress a part beyond its ratings, it's bad practice.

There is probably a service bulletin somewhere to that effect, with the recommendation to change it to 5 watt.

In any case you will probably not be able to source a 2 watt resistor, and if you do, it will be physically smaller than an IRC BT 2watt.

Not sure at the moment as to where I got them but I have bought in 2 & 3 watt resistors as they are in my stock here. Occasionally needed for principally cathodes and not necessarily radio.

Well, I changed the caps and resistors and now I have no sound. power is there, the turntable goes but can't hear anything. What have I done?
Cheers