RCA 18538A: Searching for data sheet

RCA's been gone a long time--that date code is probably the 45th week of

Cheers

Phil Hobbs

At one point RCA did use all-numeric part designators, e.g. the 40673 dual-gate MOSFET of my youth, but AFAICT their power parts from that era used the Motorola-style convention, 10N04 etc.

I had a squint at the RCA databooks on archive.org, which are all OCRed, but didn't find anything.

Cheers

Phil Hobbs

gly

RCA used that range of numbers for house number parts for their customers. I ran into this in the '70s, when someone wanted a commercial alarm system repaired. OEM bankrupt, RCA wouldn't release the data.

Yeah, a house number sounds quite likely. BITD when I was building satcom equipment for AEL Microtel, we had a lot of house-numbered parts. There was a paper cheat sheet so you could look them up in databooks. IIRC they were longer numbers, though.

Cheers

Phil Hobbs

Hi Phil,

many thanks. What do you think: "normal" BJTs or Darlingtons?

Ciao

Reinhard

The old story ... .

Ciao

Reinhard

Darlingtons are pretty slow for that use, so I'd suspect a regular NPN. Do you have a schematic? I've never designed an off-line switcher, but some folks here probably have.

Cheers

Phil Hobbs

This was my guess, too.

Of course, no. I reckon I have to do one of my favourite activities: reverse engineering ... ;-(

Sighing

Reinhard

Or, purchase a new ballast, or maybe better, switch to an LED fluorescent replacement, with its new suggested ballast. You can reverse engineer that, to learn something useful.

Winfield Hill schrieb:

Unfortunately ;-) I belong to that kind of people who would rather try to fix something than throw it away and buy something new.

Ciao

Reinhard

OK. There probably aren't that many critical specs involved, so with a little information, we might be able to suggest a usable part.

Tell us all about the lamp, its power rating, its size, bulb info, etc. Tell us everything you can about the damaged part's package, and what else it's working with on the PCB.

At a former employer, we got a shipment of 3000 of SK4093 from TI, by mistake, intended for Burr-Brown. Free transistors! It was a high-beta, selected PNP, a wonderful part. I designed a lot of stuff with them.

Winfield Hill schrieb:

Many thanks for your offer.

This

is one of the two blown transistors (TO-220).

This

is a picture of the ballast's upper housing part and PCB.

I'm thinking about using two Philips BUX 84 transistors as replacement fo the 18538s.

Ciao

Reinhard

I'd say, go for it. But maybe someone else more knowledgeable will chime in.

Is it a self-oscillating half bridge?

There would be a 3-winding toroid or bead in the viscinity of two identical power fets.

Once upon a time you'd use BUT11 or MJE8502.

They tend to be badly duplicated, these days.

RL

Ditto, but you should consider the age of some of the other components in the ballast, if you're going to get continued use out of it.

Likely a new ballast would fit inside the old hardware, to address whatever lamp type makes most sense.

RL

As others have suggested , you be far better to switch to high efficiency t ubes with 88 Lumens per Watt and 20k to 50khr MTBF The T8 tubes in 4ft len gths are about 30W and if you get tri-phosphor, you will get smoother spect rum and better daylight with 4500?k to 5000?K choices. Ma ny make them and the tubes short both pins at each end as there is no heate r and only micro-amalagam content. They look better than LEDs for over cou nter lights under cabinets. The MTBF depends on the number of starts and n ot the hours of use so if you left them on all the time its 50k hrs.

The quad tube ballasts have a common ground and 4 independent outputs so yo u can use 1 to 4 outputs without any interaction between them. They are als o silent and flicker free at 120Hz with the phosphor decay time.

Agreed. For any novices reading this thread, it's easy and smart to check these parts with a good multimeter. You may to unsolder one lead to get a valid reading. The parts which dissipate heat or are subjected to high voltages are my first to be questioned, and all aluminum electrolytic capacitors.

If we assume the part is take from their normal catalog, then in this book from 1978,

on their page 8, you may see some high-voltage NPN in a TO-220 like: TIP48 Vceo(sus)=300V, IC(max)=1A, fT=5MHz TIP49 Vceo(sus)=350V, IC(max)=1A, fT=5MHz TIP50 Vceo(sus)=400V, IC(max)=1A, fT=5MHz

Maybe RCA selected/tested Vce the TIP50 for Osram. I don't have a 1980's version of the book. I'm sure you could find better-rated devices in today's market.

Regards, Rich S.

Dear experts,

so I soldered two BUX 84 as a replacement; since I had a few handfuls of this type lying around, I selected a pair with same hfe. Fortunately, the part worked right away after connecting it: hurray!

To all informants thanks a lot!

Best regards

Reinhard