UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post - My first antique TV-Olympic Model 755-need help.

Argus25 · 16th Oct 2017, 2:50 am

Chris,

I think you are referring to C18. This capacitor has the same effect, from the alternating current perspective, if it is connected across pin 3 to ground or pin3 to pin 4. In the pin 3 to pin 4 case you will see it is across the primary of the audio output transformer, this provides high frequency cut for the sound. In this instance the capacitor has very little DC component across it, just what is dropped across the transformer primary.
In the case where its grounded it has the full DC plate voltage to contend with as well as the AC currents, but that is ok if it has a decent voltage rating like well over 400V. I would use a 600V rated capacitor here with the ground connection and if you have a 1kV rated one all the better.

As you could see, pin 4 is bypassed to ground at audio all frequencies by the electrolytic caps there.

Probably a good thing you are getting rid of those black bumblebee caps, that are notoriously bad at this age, but I don't think a problem with this capacitor relates to your current picture issues. Can you post a photo of those ?

16th Oct 2017, 2:50 am	#54
Argus25 No Longer a Member Join Date: Oct 2016 Location: Maroochydore, Queensland, Australia. Posts: 2,679	Re: My first antique TV-Olympic Model 755-need help. Chris, I think you are referring to C18. This capacitor has the same effect, from the alternating current perspective, if it is connected across pin 3 to ground or pin3 to pin 4. In the pin 3 to pin 4 case you will see it is across the primary of the audio output transformer, this provides high frequency cut for the sound. In this instance the capacitor has very little DC component across it, just what is dropped across the transformer primary. In the case where its grounded it has the full DC plate voltage to contend with as well as the AC currents, but that is ok if it has a decent voltage rating like well over 400V. I would use a 600V rated capacitor here with the ground connection and if you have a 1kV rated one all the better. As you could see, pin 4 is bypassed to ground at audio all frequencies by the electrolytic caps there. Probably a good thing you are getting rid of those black bumblebee caps, that are notoriously bad at this age, but I don't think a problem with this capacitor relates to your current picture issues. Can you post a photo of those ?