Zenith 25EC58 Restoration Thread

[vol.2]

Originally Posted by TinCanAlley

I tested them and the 68pf tested as 56pf with an ESR of 21kohms and the .0047 tested as .0038 with an ESR of 411ohms. I tested them for value at 100Hz and ESR at 100kHz. That is correct? When the new ones arrive, I'll check them the same way.

Yeah, that ESR sounds way too high at 100kHz.

It's worth noting that you would have to have a fairly expensive and fancy tester to get a really accurate reading on something as low as 68pf, but I think it's safe to say that those are bad ~kohms, or 411ohms.

You should test the new ones before you put them in to see if your meter might be misleading you for some reason. Cheaper testers might not be able handle really small value caps. If the new caps also test crazy high ESR, then you know something's up

[TinCanAlley]

Originally Posted by vol.2

Yeah, that ESR sounds way too high at 100kHz.

It's worth noting that you would have to have a fairly expensive and fancy tester to get a really accurate reading on something as low as 68pf, but I think it's safe to say that those are bad ~kohms, or 411ohms.

You should test the new ones before you put them in to see if your meter might be misleading you for some reason. Cheaper testers might not be able handle really small value caps. If the new caps also test crazy high ESR, then you know something's up

It was kohms. I did read that lower values and higher voltage ceramics don't measure will with basic ESR testers. I will definitely test the new ones and compare the reads to see if my tester isn't up to the task.

I do have a question you might be able to answer. The chassis is hand built, so when they are building them is there instructions on lead length for certain components, or is the length determined by fit and clearance? The reason I ask is the 68pf was pretty much bottomed out on the pad, so I had to clip it as high up toward the body as possible, leaving short stubs sticking out of the buckets. I plan on sitting the new leads into the bucket and using a small tip to reach the inside of the bucket and then flowing more solder into it. Since this cap had very short leads, do I need to do the same or can they be longer? I wasn't sure if they were short based on design or just that the cap fit better lower down. I know, odd question.

[vol.2]

Originally Posted by TinCanAlley

The chassis is hand built, so when they are building them is there instructions on lead length for certain components, or is the length determined by fit and clearance?

That would be determined by best practices at the time. Lead length could absolutely make a difference in specific situations, but I'm not familiar enough with the make of your TV in general to know all of the spots that would be sensitive. I would assume that anything involved in a trimmer circuit would be important as they could pick up interference.

The older guys in the Solid State forum will be able to tell you a lot better as they know the 70s US make stuff really well and I don't.