Author Topic: Remember to change your ceramic capacitors!  (Read 1144 times)

AlexanderMartin

  • Sr. Member
  • ****
  • Posts: 340
    • View Profile
Remember to change your ceramic capacitors!
« on: February 27, 2016, 12:59:51 AM »
Ceramic capacitors in cathode network, and in audio coupling circuits, are total garbage, and you can get a real performance upgrade from changing them to film. They change capacitance with temperature, they are terribly microphonic, and are quite difficult to match for equal capacitance stages in stereo amps. Don't believe me? Here's an experiment done in real time: https://www.youtube.com/watch?v=67M7fsbLUIU
15:19 shows how a ceramic capacitors value can decrease with heat, something that will severely harm any coupling circuits with capacitors very close to the tube pins.
20:22 shows how they pick up noises around them at a fairly noticeable point.

If you want to get the most out of your gear, change these out. They were cheap caps then and cheap caps now.

Consoleman

  • Hero Member
  • *****
  • Posts: 696
  • Southeastern PA
    • View Profile
Re: Remember to change your ceramic capacitors!
« Reply #1 on: February 27, 2016, 07:48:12 AM »
I did this to all my Maggies on Alex's recommendation, and it does make a difference. Capacitor technology has moved on in the last 40 years and there's no harm in upgrading.
Mark

Motorola Minion

  • Hero Member
  • *****
  • Posts: 541
  • Southern Pennsylvania
    • View Profile
Re: Remember to change your ceramic capacitors!
« Reply #2 on: March 02, 2016, 09:11:44 AM »
I knew that despite not failing like wax-paper caps do, there was a downside of ceramics ;) the temperature-dependent value (NPO) is why they work lousy in television sweep circuits compared to film caps.
Ceramics seem best employed as de-coupling for RF, where this undesirable characteristic is not an issue.

I will do this to every tube unit I restore, namely Motorola who used a lot of them. Thanks Alexander!
Tubes - Magical - Tubes

Dave

Motorola Minion

  • Hero Member
  • *****
  • Posts: 541
  • Southern Pennsylvania
    • View Profile
Re: Remember to change your ceramic capacitors!
« Reply #3 on: March 03, 2016, 12:54:09 PM »
Disregard my reference to NPO caps. After watching the video, I zeroed in on all my Motorola's preamp chassis ceramic caps ( and there are many ::)

Imagine a cap that varies with vibration, applied DC and temperature >:( , a bunch of them screwing up your HiFi from bias to equalization.
Tubes - Magical - Tubes

Dave

Ken Doyle

  • Jr. Member
  • **
  • Posts: 59
    • View Profile
Re: Remember to change your ceramic capacitors!
« Reply #4 on: March 04, 2016, 07:27:45 AM »
Go easy replacing NPO capacitors in the tuner section, they're often used to compensate for warm-up drift.




Motorola Minion

  • Hero Member
  • *****
  • Posts: 541
  • Southern Pennsylvania
    • View Profile
Re: Remember to change your ceramic capacitors!
« Reply #5 on: March 04, 2016, 10:56:49 AM »
Go easy replacing NPO capacitors in the tuner section, they're often used to compensate for warm-up drift.
Definitely not touching anything that is not audio frequency on the receiver until past the FM limiter and AM detector, in an audio amp stage - specifically, only 1 nf (.001 mf) and higher caps.

As a rule, mylar film an polyprop. caps are going in for  discs and paper caps, within the mpx adapter, preamp and output chassis. On a Motorola these seem to be .001, .002, .005, .01 and so on. I also have a console RP with a Magnavox AMP 185 BB chassis that should be a good one to try first....



 
Tubes - Magical - Tubes

Dave