PYE P 35

[Terry]

It sounds as if you need a crash course in the resistor colour code! Try this:



Note that the third band is the multiplier: I prefer to use it the way I was taught by referring to the multiplier as the number of zeros - it works out the same but is much simpler.

So in your case, red, red, yellow = 2 2 4, thus 22 & 0000, = 220,000Ω or 220k

The grey solder joint you refer to is known as a 'dry joint' and is created when something moves before the solder has solidified, causing the solder to adopt a weak crystalline structure. It could have occurred in production if nobody else has had cause to touch it since - but it could just as easily have happened last week - it isn't caused by old age.

[Crackle]

The manufacturers component list is a little confusing.
For R21 (V4 cathode resistor) it has what appears to be a ditto along side it, making it appear that it is 150 meg, it should be 150 ohms. Ignore the 2 dots which look like dittos, they are only there to make following across the line easier. All the resistance values are listed in ohms unless they have meg. against them.

Mike

[Terry]

A couple of other points:

First, have you checked the value of those 220k resistors? perhaps the original had changed value and whoever replaced it (and created the dry joint!) couldn't be bothered to cut off the other end of the faulty one?

Second, you can make your posts much simpler and clearer - thus easier to understand - and save yourself a lot of unnecessary typing by observing these tips:

Anyone who can help you will know exactly what an EBC33 is and what its function is in this set. (It might be different if we were discussing a TV with several identical valves performing various functions in different parts of the set, but that obviously isn't the case here)

Use the correct designations for component values so that your mu F should be µF, although the greek letter mu is usually replaced by a lower case u, thus uF. Similarly 'meg' is simply M, meaning a million - be careful about the case as m means milli (one thousandth)!

Another Greek symbol you will encounter is omega: Ω but there isn't a lookalike character in the alphabet so it was traditionally typed in full: ohms. However, in recent years, it has been common to use R, so 270Ω = 270R.

Another modern convention is to use a single character for the multiplier and put it in place of the decimal point. Particularly useful if you are writing values down when the point might not always come out clearly!

Thus for resistors, you will see 2M7, 2k7 or 2R7 and for capacitors, 4u7, 4n7, or 4p7. You may not be familiar with the n which stands for nanofarad - 10^-9, but it saves an awful lot of noughts! I haven't got the service sheet you are using but I bet you'll find values like 0.001uF or 0.005uF. 1n and 5n are much simpler, although often written 1n0 and 5n0. You will find waxed paper capacitors labelled 0.1mfd or even 0.1MFD. Millifarad? Megafarad? No, everybody knew you couldn't make a one millifarad capacitor, let alone a one Megafarad one, so it just means just microfarad!

You might say that these markings broke the rules but they became standard practice before there were any 'rules'.

As I said, you will find capacitor values like the 0.005uF that has already been mentioned. Don't panic when you find they don't exist any more! Capacitor tolerances used to be so poor that values followed a simple 1, 2, 5, 10 sequence but things have improved over time and the E6 values in the tolerance table I linked to have replaced them so, today, you will use a 0.0047uF (or 4n7) to replace it.

[Refugee]

I have just spotted that that the electrode capacitance figures all be it not that important right now shown on the data sheet at the radio museum are quoted as uuF (micro-micro-farads). We now use picofarads (pf) so things could get more confusing if we are not more careful.
http://www.r-type.org/exhib/aai0077.htm
Click on the PDF logo.

[Terry]

Plus ça change ...

I find it fascinating that the high quality typewriter (or whatever it was) that was used to produce those data sheets has a modified character set which includes µ and the funny symbol used for the footnotes on page 1, where anybody else would have used * and **, but does not include Ω, so that it has to be spelt out in full everywhere it would normally have been used.

I'm wondering when picofarads became the normal way of expressing small values. The nanofarad only came into use many years later.

There seems to have been a reluctance to use ρf or pf (or even µµf!) A 1937 issue of WW, selected at random, includes the design for a 4-waveband radio. The parts list includes values as small as 0.0005 mfd (!) and 0.0001 mfd. How much simpler would it have been to use 500pf and 100pf? I was surprised not to find anything smaller, thinking of all the trimmers that would be needed but they cheated! The tuner head was bought pre-assembled, so no values given!

Both a WW and a PW from 1951 used pf although when I first got interested in radio as a schoolboy in the late 50s, it wasn't unusual to find circuits in one quite recent library book I remember that used 0.0005µf tuning capacitors. So, it appears, it was each to his own for a very long time!

However, when the nanofarad first put in an appearance - mid 60s? - virtually overnight, everybody seemed to have adopted it!

Strange old world, ain't it? (Well, I was an Essex boy, weren't I?)

[Terry]

Spot the odd men out.

I was browsing through that 1951 issue of PW and came across this component list. The capacitor list is interesting!

[Lindsay]

Hi All and I much appreciate all your comments. I am trying to be a good pupil and am plumbing the ancient depths of what I once thought I knew.
  I had been certainly misreading the colour code but the 16k came from trying to work out the value of two 220k resistors in parallel, one of which had become detached. I still can't work out why reattaching the detached resistor had such a remedial effect.
  A 4n7 is on order (actually 3 of them) so I will replace the output valve capacitor before it blows up when I get it. I remember they were referred to as 'puffs'.
  I misread the double dots as dittos and the 150meg  was therefore not meg but k.
   Thank you Crackle, Ppppenguin, Refugee and Crackle for your patience and advice.
   I once got a No 18 set to go from Northern Scotland (Morayshire) to the Channel Islands and scored 5 and 7 ( admittedly we used a tuned dipole) I think it was a record.
   Have a good Christmas.

[ppppenguin]

" I misread the double dots as dittos and the 150meg was therefore not meg but k"
Not even "k". It was 150 ohms. Most now write 150R since capital omega (the official ohms symbol) is not always easily available.

"...but the 16k came from trying to work out the value of two 220k resistors in parallel,..."
Now I'm really puzzled. A pair of 220K in parallel is simply 110K.

" A 4n7 is on order (actually 3 of them) so I will replace the output valve capacitor before it blows up when I get it. I remember they were referred to as 'puffs'."
Again I don't understand. "puffs" is a common spoken abbreviation for picofarads. 4n7 would therefore be 4700 "puffs".

[Crackle]

C20 is the odd one out (spacing)
But why is that important?
Mike

[Terry]

As Jeffrey says, working out the value of two equal value resistors in parallel is easy - just divide by two.

Where the fun start is if the values aren't equal. The formula is then

1/Rt = 1/R1 + 1/R2 + 1/R3 etc.

However, normally you will only be concerned with two. If they are not the same value you will need to use that formula but it can be rewritten for two values as:

Rt = R1 × R2 / (R1 + R2)

which is much simpler. In practice, you will rarely need to use it. One case where you might is possibly to replace a critical high wattage cathode bias resistor when all you've got in a suitable rating is too high a value (but not much higher!)

You've got a lot of lower wattage rating resistors in various values, so the question is: What value resistor can you put in parallel with the one you've got to bring it down to the required value? Simple - take a rough guess and use the formula.

In this modern day and age you'd probably cheat and use an on-line calculator - of which there are many!

I've never encountered 'puffs' before, either. It is always 'puff' in the singular as a verbal version of pF (but you never, ever, write pFs, do you?)

'Uff' doesn't work in the same way but 'mike' is commonly used, as in 'a point one mike' - I don't think I need to explain why!