Another RCA CT-100 discovery B8001599

[dtvmcdonald]

"The Video IF decoupling capacitors are ceramic disc 820pf. DigiKey and Newark (I did not investigate Mouser this time lol) no longer carry the old style ceramic discs."

I looked ... both Mouser and Digikey have totally suitable, totally ordinary disk ceramic
caps. Both have over 40,000 in stock! I used these in my CT-100 (various values) and
they work and look just fine, albeit some are blue.

[Penthode]

Originally Posted by dtvmcdonald

"The Video IF decoupling capacitors are ceramic disc 820pf. DigiKey and Newark (I did not investigate Mouser this time lol) no longer carry the old style ceramic discs."

I looked ... both Mouser and Digikey have totally suitable, totally ordinary disk ceramic
caps. Both have over 40,000 in stock! I used these in my CT-100 (various values) and
they work and look just fine, albeit some are blue.

Can you show me the link? I looked and the 820pf ceramics bore no resemblance to the original. I have previously used Newark, Digikey and Mouser for years.

The NOS I bought from eBay looks a very close match.

[Yamamaya42]

Originally Posted by Penthode

Can you show me the link? I looked and the 820pf ceramics bore no resemblance to the original. I have previously used Newark, Digikey and Mouser for years.

The NOS I bought from eBay looks a very close match.

I tend not to trust most capacitors, resistors, found on eBay anymore, and especially transistors
just too many fake parts.

[Penthode]

Originally Posted by Yamamaya42

I tend not to trust most capacitors, resistors, found on eBay anymore, and especially transistors
just too many fake parts.

I agree wrt ebay and transistors. I have been burnt a few times. However if the seller is in the US with what appears to be NOS vintage resistors and ceramic capacitors I have had no problems. When wanting to keep the original appearance I have patently searched for just the right part.

It must be just me. I even baulk at newer metal film resistors which do not match the older carbon composition resistors in older vintage equipment. For 1930's sets, I have a store of older dog-bone style resistors.

I used to restuff paper capacitor but do not bother anymore and certainly the gleam of an epoxy dipped capacitor does not look too out of place. I will use modern film capacitors of a higher breakdown voltage in order to ensure the component is of a physical size roughly equivalent or only slightly smaller than the original.I will always restuff electrolytics though.

Which reminds me, I have a question on capacitors used in 50's set vertical sweep circuits minus the blocking oscillator transformer. I have found that it appears the capacitors are critical in that proper capacitor characteristic choice is essential for maintaining good sweep linearity during warmup over a half hour or so. Has anyone else had this problem?

[Penthode]

Been cleaning the considerable gunge off the chassis this week. Removed the high voltage compartment and the selenium rectifier frame to give it a thorough clean. Started replacing paper capacitors in the HV cage and now that it is clean have given it a thorough inspection.

Whilst making checks around the selenium rectifier, found a fuse blown and a jumper wire which had been placed across it. Not good. Then the resistive ballast if that is what it is called I examined and found part of it open. Closer examination revealed it appears to be simply a voltage dropped with an 800 ohm and a 300 ohm resistances to each drop the 400v DC supply to 285v. 115v across the 300 ohms dissipates 41 watts and 800 ohms 16 watts. The 300 ohm section is the one open.

It looks to me a bit of a bad design wasting 56 watts like this. That is a good chunk of the total 475 watts the setg consumes. I guess power was cheap in those days!

Anyhow think what can I do to salvage this? I found a 50 watt 330 ohm and 25 watt 820 wire wound chassis mount resistors back to back will just fit the 30cm diameter ballast container. But that is a lot of power to dissipate.

Has anyone else dealt with this or have any ideas?