I have recently purchased a 40s battery powered 4 tube radio, Well, The chassis without the box. I would very much like to recap it, But I dont know enough about electrical engineering to make out the rating on the paper capacitors and translate them to modern values. I know not to touch the micas. It seems to be an all dc radio with no means of accepting an ac input.
The tubes are:
1A7GT Oscillator
1N5GT IF Amplifier
1H5GT audio demodulator/ first audio stage
and finally a 3Q5GT as the power amp.
The radio wants two voltages in, a 90v 12ma max tap for B+, and 1.5v .25a amp to the filament voltage or A+. With a stated max output of 250mw to a 3.2 ohm voice coil in a permanent magnet speaker.
The datasheet I found states it has 12 capacitors, most of which are paper.
C-1 Paper .1mf 200v
C-2 Paper .05mf 400v
C-3 Variable tuning cap (do these go bad?)
C-4 Paper .01mf 400v
C-5 Paper .01mf 400v
C-6 Mica 100mmf 500v (This one is most likely fine because mica)
C-7 Paper .002mf 400v
C-8 Paper .005mf 600v
C-9 Mica 100mmf 500v (another mica to not touch)
C-10 Electrolytic 10mfd 150v
C-11 Paper .005mf 600v
C-12 Paper .5mf
As far I I am able to wrap my head around the mfd is analogous to the ever present µF that seemingly everything these days uses in abundance, the mmf ratings listed are somewhat irrelevant because mica caps dont really go bad, well, Sometimes they do as is with everything eventually, But it is somewhat rare.
So my main question here is how do I read the values of the paper capacitors, and what do I replace them with? This isnt the only tube project I have, but it is the first I feel comfortable actually tackling, seeing as how the voltages are "Relatively" low.
The tubes are:
1A7GT Oscillator
1N5GT IF Amplifier
1H5GT audio demodulator/ first audio stage
and finally a 3Q5GT as the power amp.
The radio wants two voltages in, a 90v 12ma max tap for B+, and 1.5v .25a amp to the filament voltage or A+. With a stated max output of 250mw to a 3.2 ohm voice coil in a permanent magnet speaker.
The datasheet I found states it has 12 capacitors, most of which are paper.
C-1 Paper .1mf 200v
C-2 Paper .05mf 400v
C-3 Variable tuning cap (do these go bad?)
C-4 Paper .01mf 400v
C-5 Paper .01mf 400v
C-6 Mica 100mmf 500v (This one is most likely fine because mica)
C-7 Paper .002mf 400v
C-8 Paper .005mf 600v
C-9 Mica 100mmf 500v (another mica to not touch)
C-10 Electrolytic 10mfd 150v
C-11 Paper .005mf 600v
C-12 Paper .5mf
As far I I am able to wrap my head around the mfd is analogous to the ever present µF that seemingly everything these days uses in abundance, the mmf ratings listed are somewhat irrelevant because mica caps dont really go bad, well, Sometimes they do as is with everything eventually, But it is somewhat rare.
So my main question here is how do I read the values of the paper capacitors, and what do I replace them with? This isnt the only tube project I have, but it is the first I feel comfortable actually tackling, seeing as how the voltages are "Relatively" low.
For example, your 0.1mf = 0.1μF = 0.1 microfarad capacitor.
Use a similar or higher voltage rating mylar film capacitor, with wire leads (not for pcb).
For example, 100mmf = 100pf = 100 picofarad capacitor.
Digikey and Mouser have a component selection filters like this one.
https://www.mouser.com/c/passive-components/capacitors/?product type=Film Capacitors&sort=pricing
Any voltage around 50V or higher is dangerous.
Use a similar or higher voltage rating mylar film capacitor, with wire leads (not for pcb).
For example, 100mmf = 100pf = 100 picofarad capacitor.
Digikey and Mouser have a component selection filters like this one.
https://www.mouser.com/c/passive-components/capacitors/?product type=Film Capacitors&sort=pricing
Any voltage around 50V or higher is dangerous.
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Nice link here showing you what to replace wax coated paper capacitors with:
https://www.vintage-radio.com/repair-restore-information/valve_capacitors.html
https://www.vintage-radio.com/repair-restore-information/valve_capacitors.html
Film capacitors are nonpolar by design - same as the paper capacitors were - so it doesn't matter.
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They do; but you can't replace it do do NOT mess with it. Yet.
If treated nice, the most common problem is dust between the plates, making scratching as you turn/tune.
If thrown in a box, the plates are bent, and it is insanely tedious to get them to alignment.
Was it made in New Jersey?
If it has not yet been shipped, ask him to tune the tuning capacitor (with the knob) fully closed
so it is less likely to be damaged in shipping.
so it is less likely to be damaged in shipping.
It has already shipped, But I did tell him to pack it well, but with more focus on the dial cover. On its way from Southfield Michigan to Florida its somehow ended up in Broomfield Colorado.. Fedex confuses me so. another pic from the ebay listing. Im not sure the seller even knows what a tuning capacitor is.
"Single". The radio is a superhet, in the AM band. It really wants two different sections. (In my town, three is better.) In the image above, the front section is masked by the battery plug.