This component - it was connected between pin 4 and 6 of the 7C5 in the schematic. My LCR meter says it's a 55nF capacitor. "47KP" could perhaps mean 47 000 pF.. makes sense? There's also a .05uF cap in the schematic. Stuff isn't exactly connected like there though, so can never be sure.
However, why the strange markings? All other caps in this radio from 1949 are properly marked, no voodoo.
However, why the strange markings? All other caps in this radio from 1949 are properly marked, no voodoo.
Attachments
47K indeed means 47000pF (=47nF=0.047uF)
P means +/-20% tolerance
No letter before the digits means 400V rating
P means +/-20% tolerance
No letter before the digits means 400V rating
Doesn't look too untoward. Pin 4 is not used, so it is a tag for the other end on the cap. 47kp (multiples of picofarad) is quite common in these old radios, and it tests good for being 70 years old.
It looks like a paper capacitor, which tend to get leaky after a couple of decades. Don't use it at places where low leakage is essential, like as the DC blocking capacitor at the input of the audio output stage of a valve radio - which is what it's used for in your radio.
Last edited:
The case is cracked. It may measure good but will start leaking eventually. Which is cheaper to replace, the capacitor or the tube it could potentially destroy?
Not any more, its junk, but originally it was a capacitor! Yes, the KP for nano is a thing, though knowing cap. manufacturers it would as likely be marked 47000, or 47000uuF, or 0.047uF or 473 - they seem to have an irrational fear of odd powers of 1/1000th, so mF and nF are rarely notated as such, tiny fractions of a uF or large multiples of pF are often seen.
This cap may predate the nano prefix, given its age.
This cap may predate the nano prefix, given its age.
Thank you very much, as always there are some extremely knowledgeable people here! I will absolutely replace the cap, no worries 🙂🙂🙂
It is perhaps taboo to continue the thread with another question, but since I managed to get you here answering (and I'm a bit ashamed to litter the forum with my topics), perhaps I can continue here..
This capacitor is the one across the output transformer (in schematic in previous post). It is a 10nf, fallen apart.. my questions regarding it:
1) What is its purpose? Seems to me it just limits frequency response? Or is there something more important going on here?
2) What type of dielectric do you think this is? Seems like an expensive part, what would do well replacing it?
3) Voltage ratings are very high - peak voltage 3000V - could there actually be such voltages here?
It is perhaps taboo to continue the thread with another question, but since I managed to get you here answering (and I'm a bit ashamed to litter the forum with my topics), perhaps I can continue here..
This capacitor is the one across the output transformer (in schematic in previous post). It is a 10nf, fallen apart.. my questions regarding it:
1) What is its purpose? Seems to me it just limits frequency response? Or is there something more important going on here?
2) What type of dielectric do you think this is? Seems like an expensive part, what would do well replacing it?
3) Voltage ratings are very high - peak voltage 3000V - could there actually be such voltages here?
Attachments
When output transformer is unloaded very high voltages might occur.
The cap should limit those somewhat to protect the transformer.
The cap should limit those somewhat to protect the transformer.
That cap is cutting hi-frequency , including audio , so the amp can't auto oscillate . It is used in radios , TVs and guitar amplifiers where full bandwidht and hi-fi is not important .
This makes sense - the radio has an option for external speaker, so some protection is probably a good idea.
As for the frequency response, based on the output tube's load requirements (and some guessing), it would seem to me this limits the output to about 8Khz. Makes sense when thinking about the audio sources it is expecting. However, would I risk anything by reducing it to 5nF (i.e doubling to about 16Khz freq response, assuming OT limits doesn't come into play)?
The 10" driver in this radio seems to reproduce 15Khz just fine.
As for the frequency response, based on the output tube's load requirements (and some guessing), it would seem to me this limits the output to about 8Khz. Makes sense when thinking about the audio sources it is expecting. However, would I risk anything by reducing it to 5nF (i.e doubling to about 16Khz freq response, assuming OT limits doesn't come into play)?
The 10" driver in this radio seems to reproduce 15Khz just fine.
You can reduce it or remove it , maybe you can hear a difference , but the output transformer probably is not made for hi-fi anyway .
Hi-fi amplifiers obviously don't use that capacitor and work fine ... and even the capacitance in the output transformer windings itself can be enough to limit the bandwidth , so it is not desirable to have capacitance there .
Hi-fi amplifiers obviously don't use that capacitor and work fine ... and even the capacitance in the output transformer windings itself can be enough to limit the bandwidth , so it is not desirable to have capacitance there .
If the unit is an AM/ Shortwave radio dont expect more than 5khz bandwidth. I have brought to life a couple of floor console radios from the 30's. Replace every coupling, bypass and electrolytic capacitor. You can leave the mica capacitors in the radio, they almost never go bad. Resistor and capacitor tolerance was a nominal 20% 5% if it was critical. The power supply voltage and heater voltage will probably be higher than what is printed in the schematic. You may need a ballast resistor in series with the primary of the power transformer to get the voltages right. You can fit a modern electrolytic inside the old electrolytic to keep the look of the radio the same.
Yes, there's a grammophone input. It was pretty high end for the time, so I have my hopes up. I'll restore it with original values first, then experiment and monitor for oscillation. That Ducati cap was not cheap, the engineers knew what they did and they put it there for a reason. For shellac records and am radio, 8Khz is plenty and anything above is just noise. I'll see if I can push it, and if too high frequencies get rolled off or creates weird harmonics, oscillation or whatever.
Here is where I bought my radio parts
Capacitor Shopping Cart for Tube Electronics
You can get a kit of common values or buy individual parts.
Capacitor Shopping Cart for Tube Electronics
You can get a kit of common values or buy individual parts.