Welcome Guest! Be sure you know and follow the Phorum Rules before posting. Thank you and Enjoy! (January 12) x

Thread Closed
Thread Rating:
  • 0 Vote(s) - 0 Average
  • 1
  • 2
  • 3
  • 4
  • 5

Capacitator polarity something new I had not heard of
#1

Has anyone else seen this video. I didn't know that (non electrolytic caps) foil caps had a polarity to them. It's based on the outside foil lead vs the inside lead of the roll. If they are installed with the outside lead to the low impedance side of the circuit its cut down the noise sensitivity of the cap. .
https://www.youtube.com/watch?v=BnR_DLd1PDI

!!!!!!!!!!!!!!!!!!!RESISTANCE IS FUTILE!!!!!!!!!!!!!!!!!!!!!!  
                           /\/\/\/\/\/\/\/\/\
                                                     
                                 [Image: http://philcoradio.com/phorum/images/smi...on_eek.gif]  Chris
#2

I would not call it polarity, but yes, in some applications this, lets say physical orientation matters.

People who do not drink, do not smoke, do not eat red meat will one day feel really stupid lying there and dying from nothing.
#3

Here's a video explaining why it doesn't matter: https://youtu.be/hJVe_JTs4fU

Short version - the other components like resistors and wiring are more likely to pickup noise. Since no one seems to care about them, why should the caps matter ? Also, if it really made a difference, why don't manufacturers mark them ?
#4

Its not always important, but the shielding effect of the outside foil does make a difference. 

The video that Bob mentions is full of misinformation. Film caps have been marked as to the outside foil connection for decades because of the inherent shielding it provided, not for any risk of shorting to ground. Until recently, even yellow film caps made by Cornell Dubilier and Sprague were marked with a band for the outside foil end. 

Contrary to what was said in the video, the scope test is an accurate measure of the sensitivity of the cap to stray signal pickup. When the outside foil end is connected to scope ground, there is less coupling to the inner foil from external fields, resulting in less noise indicated on the scope than when the leads are reversed. If the noise indicated is less with the proper orientation of the outside foil in the scope test, then it will also be less when properly connected in circuit. This is not magic or rocket science, just basic physics.

I typically use the scope test to mark the outside foil on all film caps I install. While it may not be critical in all circuits, RF and IF stages can be prone to self oscillation, and why take chances if you can replace a cap with the orientation that the design engineer originally specified.
#5

Long time no post!
Good the hear from you.

Terry
#6

Hi Terry. Yes I have been taking a break from radios for a while. 

When spring came and the weather got nice, I started working on restoring old cars again and am just getting back into radio. 

Its good to be back!

Mike K. WA2YGA
#7

Agree, but the smaller physical size and construction of modern equivalent components obviates some potential orientation issues for most all consumer grade applications. It is still very much advisable to duplicate original lead dress even if it means lengthening a component's lead once in a while. Careful tack and reverse of suspected critical components is also a possibility should there be a problem.




Users browsing this thread: 2 Guest(s)
[-]
Recent Posts
462ron
Hi Levi, here’s just a thought. Most radios run the oscillator higher than the dial setting. Say you set your radio to 1...462ron — 10:10 AM
1930s Stewart-Warner Tombstone Radio need help identifying model number
Another Update: I found a couple of damaged coils inside this radio that might have something to do with why this radio ...captainclock1988 — 10:51 PM
6TPZ and 5TPO Radio Help
If you are still on 5TPO, you lost me there. What X7? What Points 1 and 2?morzh — 08:37 PM
6TPZ and 5TPO Radio Help
Quick progress report: X7 is broken. Only one leg soldered, the other missing and the diode is cracked. I've replaced...R3Sons — 05:05 PM
6TPZ and 5TPO Radio Help
Oh...and you have electrolytic caps there. All need to go and be replaced.morzh — 04:36 PM
6TPZ and 5TPO Radio Help
Thanks, will do.R3Sons — 01:25 PM
1930s Stewart-Warner Tombstone Radio need help identifying model number
UPDATE: I was able to pick up a signal generator on the cheap (amazingly enough) on feebay and I did an IF alignment fol...captainclock1988 — 09:53 AM
Philco 91 Schematic
Hi Rod, The resistor connects to pin 4 and the ungrounded side of block 9. From pin 9 of the RF tube to one side of ...dconant — 09:34 AM
Just got a 49-1613 need to know...everything!
I just found your post. I have this exact same model, and have had it since 1985 when I was 15 years old! I performed a ...MuzzcoVW — 09:11 AM
B&K 1077B no video
Hello Tim, I would if it's a leaky Capacitor So are all 3 of those B- voltages low then ? Sincerely Richardradiorich — 01:55 AM

[-]
Who's Online
There are currently 6060 online users. [Complete List]
» 2 Member(s) | 6058 Guest(s)
AvatarAvatar

>