Fixing a 100 years old potentiometer (PWJ230)

On my Saba radio from 1927, all four adjustable resistors were bad because of corrosion. So I went one step further to make the radio (hopefully, probably) work again...
These resistors are there to adjust the heater current of the four tubes. For example to adjust the output volume because there is no volume pot.
Please watch the SABA video PWJ227 for more details about the radio...

[@Petertronic]

Amazing we are now at the era where radio sets are becoming a century old. I love watching you work on this Saba radio.

[@jimsvideos7201]

The engineers who designed this couldn't dream of an instrument like your oscilloscope, and we can't dream of that much real brass, wood and labour in a table radio.

[@PlaywithJunk]

Yeah times are different... just imagine to bring an iPhone back to 1950. 🙂

[@EdwinSteiner]

The build quality is amazing. They had such great metal working back then.

[@HyperSpaceProphet]

When cleaning metallic contacts, I find that instead of a wire wheel, using the white draftsman erasers *or the pink ones if the oxide is really hard) will clean without removing as much metal. Nice work though, and really nice old receiver.

[@Duracellmumus]

There is no need to be replace when gets open just screw down the plates and rewind with new wire. This feature is so relaxing

[@odindimartino597]

The voltage of the heather battery is greater than 4V so the variable resistors are here to compensate the voltage variation and adjust the gain of the tubes. Also, this kind of tube don't have a bright heather except maybe for the last one driving the speaker

[@garymucher4082]

Now that was interesting to see how they solid wired the entire circuit and to help against shorting they wrapped the solid wires with what looks like some type thread. Ingenious to see that.

[@PlaywithJunk]

the resistor wires are just wires with an oxide layer, that prevents shorts. I guess it comes like this from an oven. The contact path is then polished blank for the slider. It seems that polishing must be repeated every 50 years... 🙂

[@janno288]

Those Rheostats are to control the emission of the tubes, sometimes also used to control volume

[@gvii]

What is the frequency range on that? And just out of curiosity, are there still any AM broadcast stations around you still? I really do love that thing to no end. It really is an immensely fascinating bit of RF history. The fact that its condition makes it look like it was just built a couple of years ago completely blows my noodle. I don't know where they were storing it, but where ever it was it was clearly very good for it. Yeah, the dials are a little beat up, but that's not a big deal. The innards are just amazingly well preserved.

[@SeekingTheLoveThatGodMeans7648]

Quite a rugged design for these rheostats. Corrosion became a problem after many years, but cleaning it off was so simple. It is as though they were designed for just that. Saba would be amazed if it could have known that its radios would still be working in a hundred years with a small bit of physical maintenance and the same tubes. I don't understand why any plausible battery power for that day would be expected to harm the tubes. Were these even thoriated filaments?

[@glasslinger]

Most likely oxide coated. Thoriated filaments glow a lot more brightly.

[@ThomasJakober]

The electron dissipation of the cathode depends on temperature of the heated cathode what influences the aplification factor of the tube. So in the AF (Audio frequency) section it controls the volume. In the first RF (Radio frequency) section it regulates the preamplifier. The second stage is the audion which has a feedback for demodulation. This needs to fine tune the amplification to prevent oscillation of the circuit.

[@lbochtler]

You forgot to mention that it also changes the transfer function curve shape. This can and will result in distortion. Would be funny to see audiophiles try it and clame its the best thing ever for volume control. That seems like something theyd do

[@ThomasJakober]

@@lbochtler Yes that's correct. Funny comment about the audiophiles 😂

[@jantepas7511]

Nice OLD technic. Good made.

[@SeanBZA]

Resistors are there to provide grid bias, if you run to zero then the current is uncontrolled, and rapidly strips the cathode, plus the tube is not going to work well as it has a red glowing anode.

[@PlaywithJunk]

Those adjustable resistors are in series with the heaters. There is no adjustment that affects the grid. A schematic diagram can be seen in my previous video about the radio…

[@SeanBZA]

@@PlaywithJunk Voltage dropped across those resistors affects the grid bias directly, as grid is connected to filament battery negative, with positive connected to the filaments directly. Those tubes need a slight negative grid bias to work, either provided by a grid bias battery or by cathode resistor that develops a small voltage across it from cathode current, though here it is mostly from heater current.

[@msylvain59]

Why not just bring it back to the retailer and do a warranty claim 🤗

[@PlaywithJunk]

Can you talk with dead people? :-)

[@MartinSBrown-tp9ji]

I wish you could talk louder on your demonstrations.

[@PlaywithJunk]

The sound level of my videos is the same or higher than most KZbin videos. Maybe you need better speakers?

[@TedBackus]

i miss when companies made their brand name on durability. now they make their brands reputation on low cost & what its gotten us is garbage. what makes more sense, buying an item you need for $10, and replacing it every year or two, or buying an item for $50 & never needing to replace it?

[@PlaywithJunk]

Things that dont break are bad business...

[@DataDashy]

thats literally playing with junk hate these tube things good luck replacing the tubes in the future btw when they break

[@PlaywithJunk]

I have a couple of old radios and I never had problems with the tubes. Most of them can still be bought, some even new. It is way more difficult to repair a device from the 1990s with some custom chips. There is no need to hate tubes 🙂 In fact it is possible to make vacuum tubes in a hobby workshop. But for chips that would be impossible.

[@l3p3]

Making chips is in principle possible, several channels demonstrated it.

[@PlaywithJunk]

@@l3p3 I know, very simple chips though. However, making a tube is more a mechanical challenge and easier to achieve. See the guy who makes beautiful Nixie tubes.

[@TLang-el6sk]

@@PlaywithJunk You most likely mean Dalibor Farný and his R|Z568M tube? And there's also a anufacturer of an IN-18 remake, Millclock.

[@ledhunters]

You are playing with your junk 🤣 hahhahahaha