It might help to understand what the values on a capacitor mean - WARNING: this started as a small explanation and kind of got away on me a bit - the
TL;DR is down the bottom, with links to what you actually need.
VOLTAGEThis is the bit that causes trouble with old caps - as they start to fail they can't handle their original voltages any more and they 'leak' DC voltage through when they should be blocking it entirely.
As a rule of thumb, most paper capacitors in valve radios can be replaced with modern 630-volt types of the same or close capacitance. This voltage rating is the maximum it can handle, and in most situations a typical valve radio won't see voltages above 630V in any part of the circuit (caps directly across the output transformer can sometimes be rated up to 1500V but this is not common).
Take for example, this Pacemaker 5151 service sheet -
nzvrshome.files.wordpress.com/2018/12/cb-model-5151-5v-bc-ac-1952.pdfthere is a list of capacitors and their voltages - 400V is the highest value, but some are lower. This mattered back in the day for two main reasons: cost, and size. Today the cost is very low (and the difference in cost between a 100V and 630V cap is negligible), and the size very small... so in something the size of a valve radio chassis with modern incomes these factors just don't, well, factor in much any more. Biggerer is betterer (to a point, anyway).
630-volt rated caps are the most common high voltage caps made today - not the only ones, just the easiest to find.
Jaycar does carry 630V capacitors - but you will need to know what you need because their staff are seldom electronics hobbyists - those days are long gone unfortunately - and I doubt they will ever return. Its certainly not a criticism of their staff, its just that component-level electronics is not as popular a hobby as it was when I was a kid. Personally I'm very grateful that they still carry these components for those of us still playing with them.
CAPACITANCEAs for the actual capacitance, old values used to be rounded off sensibly, while modern values (your set was one of the early examples following the new standard) follow a 'preferred value' mathematical formula for overlap of tolerances and temperature coefficients (look up the E-series for resistors, capacitors and inductors if you're interested in a deeper explanation of that) so they make less sense to the average person.
For example: the old value might be 0.05uF, but the modern equivalent is 0.047uF (in E12, the most common E series).
TOLERANCEOld paper caps were also typically +/- 20% or more meaning a 0.1uF cap could be between 0.08 and 0.12uF when new. I've actually seen them specified as +50% -20%, +100% -20% and other variations so the value could be waaaay away from what the service data specified but the original engineer designing the radio knew this and it was taken into account...
This means unless specified as a tight tolerance component (you will find these in certain parts of the set but not generally with paper (tubular) caps) you can typically go with the "close enough is near enough" theory.
Manufacturing processes are far more accurate these days, the foils and dielectrics are more uniform as well - so commonly available modern caps off the shelf are often +/- 10% (which is the overlapping tolerance specified in the E12 series).
In reality the old cap value could be anywhere in the ballpark.
VALUESThe other thing that can cause confusion is the way the capacitance is specified... uF vs. nF vs. pF - these are SI units, micro, nano, and pico respectively. Each is 1000 times smaller than the previous: for example 1uF = 1000nF and 1nF = 1000pF.
Old circuits tend to specify almost everything in uF (in other words if the schematic says 0.05 then it means 0.05uF) - although sometimes uuF (which is old-school speak for pF, although these smaller values were typically silver mica caps not paper ones). And nF was practically never used back then, but today that is the value specifier most often used for the kinds of values used in valve radios (as you will see on the Jaycar site for their 630V caps) - so you need to be able to convert these.
So:
0.05 = 50nF (and in your case 0.047 = 47nF)
MARKINGSThe actual markings on a modern cap in this size range are (annoyingly for those new to this) in pF will have something like
2J473J which translates as:
2J - this is the voltage rating, 2J = 630V (2A = 100V, 2E = 250V, 2G = 400V)
473 - this means 4, 7, and 3 zeros and, remember, is in pF:
47000pF - which you divide by 1000 to get
47nF
J - this is the tolerance - J for 5%, K for 10% - either will be fine
Sometimes this might also be written as
473J630V or similar- it's the same thing
The package might also have something like
CL21 or
CBB22 on it - this is the specification of the physical construction and not super-important to paper-cap replacement in an AM valve radio.
YOUR ACTUAL QUESTIONSo the TL;DR:
C6 - 0.047uF 400V - replace this with a
0.047uF (47nF) 630V C4 - 0.1uF 350V - replace this with a
0.1uF (100nF) 630VC9 - 0.022uF ?V - replace this with a
0.022uF (22nF) 630V - but check the voltage on the cap as this one is across the output TX although I'd expect it was originally 500V or similar
Hopefully thats helpful (and hopefully its all correct - someone will jump in and correct any whoopsies I'm sure I have probably made)... Pictures might have helped, maybe I'll add some
Cheers, Steve
