Thinking about my BLOWUP. I likely caused it when I was testing voltage between filament leads of the rectifier tube, maybe I shorted them causing the blowup.

You really need to replace all the paper capacitors in the set, they're all leaky, and one or more of them could be shorted. While you're at it, you should check or just replace all the small carbon resistors while you are at it. Once this is done, it will make diagnosis much easier, and lessen the chance of damage to critical parts in the set. The cited references do have expected voltage readings. You will no doubt see higher readings in some of the circuits because modern digital an VTVM meters do not load down the circuit at all.

Could be. Voltage on the plates is AC and the only reasonable measurement is between each plate the the center tap. This should be the same for each plate. Do not attempt to measure between the plates and filament of the rectifier. The reading would be meaningless, and might damage meter andor the set. The filament (which also serves as the cathode is also the cathode will be read only in DC and is measured to the negative of the first filter capacitor.

Be certain of the polarity when you replace the capacitor, and make sure you have not fried up any resistors in the voltage divider. Also do not operate this set on it's side, because the rectifier (80) may short itself and self destruct in this position. Even totally upside down is dicey. I use jumper cables carefully placed, put the chassis up on a couple of wood blocks, hook up the meter, double check everything, then power up to take readings. Haven't lost any lately.

Richard

Go by the schematic for polarity. I wouldn't go by it worked at first but later blew. Some electrolytic caps will seem to work reversed for awhile, get hot and then blow.

If filaments light and a radio has B+ voltage on the first filter cap usually there isn't a need to measure AC voltages. Only the transformer supplies AC voltage. All others can be read on a DC scale of the meter.

Norm

The polarity was right --- (-) to 500k resistor (it measures 65k ohms), to 1100 ohm filter resistor and to speaker field.

Should I replace the blow cap and heat up again or replace all old caps before putting power to it? I do like to get a radio to work before I make major replacements in case I make mistakes, which I usually do!. FUN! FUN! FUN!

Richard

Replace the cap again, 10 mf @ 450 volts will work. Unlikely this cap would have blown from anything wrong in your radio. Even if a tube shorted the first cap might blow but not this one.

I replaced the blown cap and did a little wiring. Power on, no blow up but no sound!

I am going to let the old radio rest for awhile, we are leaving for the northwest tomarrow for a month. Hope to pick up another radio. Thank you for your help. When I return I will start another post.

I am back. While I was away a friend of mine found my problem! A solder blob was shorting a trimmer to ground. After the blob was removed the radio came to life. A simple mistake, but hard to find!

The radio still fades. I will start to replace the old caps, hopefully this will solve the problem.

Be careful loading one stage at a time. That set is back biased and will not run correctly until the correct bias voltages are developed across them: That requires all of the correct current.

Marc

What do you suggest, Marcc?

When the fading happens, all I have to do is turn the volume up and back then the fading disappears?

Pins 2 & 3 (small pins) are AC "B" Plates on the 80. Measure from them to CT with the tube out. Not across them.

With an 80 tube: 400V AC on the plates, should give an output of around 390VDC (loaded down). I have not looked at a circuit but I would, if there are heater tubes involved, expect quite a substantial initial surge voltage, prior to the conduction of the heater tubes. I normally monitor the voltage on start up.

Modern electrolytic caps rarely list the surge volts as the old ones did (the most common being 525 SV). With the voltages noted I would not go below 600V. I will not normally go below 500V on a 5Y3 that is running a 250VDC B+ rail.

I have had 450V caps fail after around 18 months on a 250V rail supplied via a heater rectifier. So there was no surge to kill them? Set now has Spragues & no issues, so it was likely a quality problem.

Marc

Back to the fading Atwater Kent. I found a week tube (24). I replaced it and like magic no more fading

Many old ecaps used on tube radio's had a surge voltage in the order of 525V.

Do not replace 450V with 450V, lest you fall into the same pit. Most of the modern caps do not have a surge rating. What may have been causing the fading is the death throes of a filter cap drawing lots of current. Fix that first.

Marc

I did replace all of the caps in the radio with little inpovment in the fading. As I said when I replaced tube 24A, the fading problem stopped The old Atwater Kent sounds like new.

As a matter of interest, how did you determine that the ecap was not leaking? Putting a short across is it not nice but rarely destroys them.

The only way to see if they leak is to apply voltage and measure the current passing through them. I in uA is nominally 0.01 x capacitity in uF x volts applied. And I have seen a few get to a certain voltage and then suddenly start to conduct hyperbolically. Two were 450V and had never been exposed to that level of voltage, prior to failing.

Marc

Congratulations! Glad you found the problems.

Another to log into the archives. looks a lot like a heater problem inside the tube. Happy ending: all good.

Marc

Thank you, to all of you. Part of the fun is gleaning the wisdom out there and hopefully making new friends.

May I ask one more question. The Atwater Kent 84 late model has 3 bass to treble settings. Is there a way to increase the treble?

While not looking at the circuit, if it is the conventional caps on the plate of the output tube type, you could try reducing one of the cap/ caps in value (not voltage)and see what happens.

Some sets have Mica's there as you still need to decouple RF.

Marc