Hi all,
Currently in the process of recapping a hand wired Pye C 17 and I've noticed something slightly odd.
According to the circuit diagram, there should be a capacitor to ground (C80 0.001mf) in the interlace/timebase circuit. However, in the actual location there is a 82ohm resistor (no resistors of this value in the component list)
This resistor is clearly original and I've seen other examples of the chassis with the same resistor (but the circuit diagram for all versions of this chassis shows the 0.001mf capacitor (pictures attached)
1. Am I an idiot who can't read a circuit diagram?
2. If not, what is the correct component? the resistor or the capacitor?
3. What would the effect be on the interlace circuit/timebase.
The rounded moulding (compared to the more squared-off cylinder of a typical composition resistor) suggests to me that it's a Hunts (possibly another make) "rat dropping" paper-inside-Bakelite capacitor, I think the coding is brown-black-red, suggesting 1000pF (i.e. 0.001uF, 1nF as the diagram indicates).
Have you tested it?- though it may of course register as a resistor after this time anyway! I evicted several of the 10nF versions of these less-than-wonderful components from the AGC lines of the two Eddystone receivers here a while back.
Yes agree its a 1000pfd cap, notoriously unreliable from what remember of them.
Frank
It is definitely a 1000pF capacitor. Nasty things and change on sight. They might just as well be resistors.......
They have various names....none printable on here but also called 'torpedo' or 'rat droppings'. Heave it out and replace it with a decent 1000pF.
How did you think it was an 82 ohm resistor when the colour code is brown, black , red, 1,0,00 with a silver band? Mind you it could measure 82 ohms......
It is definitely a 1000pF capacitor. Nasty things and change on sight. They might just as well be resistors.......
They have various names....none printable on here but also called 'torpedo' or 'rat droppings'. Heave it out and replace it with a decent 1000pF.
How did you think it was an 82 ohm resistor when the colour code is brown, black , red, 1,0,00 with a silver band? Mind you it could measure 82 ohms......
One of the last sets to use the two-diode Pye positive interlace filter. R91 (220Kohms) and capacitor C78 (220pF) form the frame sync pulse integrator, time constant >40microseconds. I think it is safe to suggest that C80 as shown in the circuit diagram is the correct component. An 82ohm resistor will result in extremely critical frame hold. The sync pulse at the grid of frame multi-vibrator V21A should have an amplitude of 25V P - P.
The later printed circuit CW17 models employ a single diode interlace filter circuit, a diode connected ECC82 in some sets.
Till Eulenspiegel.
It is definitely a 1000pF capacitor. Nasty things and change on sight. They might just as well be resistors.......
They have various names....none printable on here
Very true.
I have said somewhere on here before that I have a strange desire to hook them up to a DC supply and make 'em pop. Kind of a sadistic streak I guess, and not the kind of thing professionals do.... 😜
To understand the black art of electronics is to understand witchcraft.
Andrew.
Have you tested it?- though it may of course register as a resistor after this time anyway! I evicted several of the 10nF versions of these less-than-wonderful components from the AGC lines of the two Eddystone receivers here a while back.
Yes, it's not nice when components are wearing the wrong uniform - you never know if it's a friend, or a foe!
You've got to watch out for those "Bumble-Bee" capacitors which have colour bands just like resistors. 1000pF = Brown, Black, Red.
Till Eulenspiegel.
Thanks for the confirmation everyone! (showing my ignorance of older capacitor forms here)
Fortunately I have are placement film capacitor at hand so it'll be heading to the bin shortly.
@Katie Bush @katie-bush very much so! Over the years, I recall various component packages that did their best to perplex end-users. Grotty PCB-oriented radial carbon comp resistors that looked like tubular ceramics, then dainty Japanese axial tubular ceramics that looked very much like dainty Japanese film resistors but with a slightly different shade of body paint. No doubt others here could come up with plenty of other examples. I haven't even mentioned surface-mount stuff yet....
Mod edit:
Fixed the mention as its syntax was incorrect.
To invoke a mention it must typed as shown below their username. As you can see (your original one has been left with a strike through), originally you put in capitals where there were none and missed the hyphen. You will know instantly if a mention is correct as it will be a hyperlink, an incorrect one will just be plain text.
Sorry- yes, I let typing fingers get ahead of brain there. Not so unusual...
Well in Australia we had one capacitor maker (UCC) release paper caps in white plastic tubes in the early 60s that looked exactly the same as their polyester ones. You had to read the markings - "Di-Pol 100" vs "Hi-Qual 100". And yes, they behaved just like any other paper cap! Watch out for them in 60s AWAs in particular.
