Hi all -
My electronics hobbies have evolved into salvaging old stuff and making fun things if I can. Some of you may have seen the NAND gate oscillator I was working on earlier. I usually just end up making LEDs blink.

Anyway, I found some old power transistors in an old HP box (I think it was a server power supply from the 1980's but I could be wrong.

Here is an image of what I am pretty sure are power transistors but I have not had any luck finding a datasheet on them. I've never seen anything from RCA before (granted there is a lot I don't know ).

Any help in identification would be greatly appreciated.

Thanks,
Doc

 

The component on the right is probably a positive 35 volt linear regulator and though I cannot make out all of the numbers on the left component, it looks like a 7921. If it is a 7921 then it may be a negative 21 volt linear regulator.

It was not uncommon for the higher power regulators to come in a T0-3 package.

hgmjr

 

Thanks! The left component reads HM 7921 on the bottom and 4-0563 on the top. The component on the right reads RM 7835 on the bottom and 4-0563 across the top.

A voltage regulator would make sense. I'll see if I can take a decent image of the board they came from. There was also two 2n3791 PNP power transistors with these two RCA components.

 

My guess is that they are the same part, 4-0563, which is a proprietary number that was assigned to them by the company that made the product you (or whoever salvaged them) found them in, e.g., a TV set or whatever. I think 7921 and 7935 are date codes, which are very common on electronic parts. (19)79 would be the year, 21 and 35 would be the weeks, when they were made by RCA.

 

Ron -
I am pretty sure this equipment was made in 1979 - there was a calibration tag I noticed on it dated from 1979.

Here is a link to image of the board - it's kind of big so I'll host it on my server at the clinic. (It's about 300 KB so dial-up users beware.)

http://www.tcah.com/images/postings/scrap-board.jpg

Doc

 

If you can draw a schematic, with the mystery parts shown as boxes, we could probably figure out what they are in general terms, but I doubt you will ever get specifications for them.

 

A schematic may be out of may range of skills ! But I can scan the bottom of the board.

http://www.tcah.com/images/postings/board-bottom.jpg

 

Where were the mystery parts located?

 

Where were the mystery parts located?

Sorry - I realized after I uploaded I didn't mark them. I've circled them in red and re-uploaded the file now.

 

Sorry - I realized after I uploaded I didn't mark them. I've circled them in red and re-uploaded the file now.

Hmmm... I know I'm colorblind, but I don't think I'm that bad. Did you check your images?

 

ooops. I refreshed the link. The red circles are kind of thin. I'll work on some thicker lines.

 

This should be better.

http://www.tcah.com/images/postings/board-bottom.jpg

I had to hit refresh on my browser to get the edited image to show.

 

Does this help? You can tell us which of the four sites the devices are located in.

hgmjr

 

Well curiosity got the best of me and I decided to open the case. Using nippers I trimmed the top off of the metal T-03 casing.

Here is a high resolution scan of the innards.


Of course I don't know any more about this piece than I did before I opened it but .....

 

Well curiosity got the best of me and I decided to open the case. Using nippers I trimmed the top off of the metal T-03 casing.

Here is a high resolution scan of the innards.


Of course I don't know any more about this piece than I did before I opened it but .....

Based on what I can see, I feel comfortable saying that there is not enough sophistication to the silicon for the device to be a voltage regulator as I initially guessed.

I believe RonH has correctly interpreted the nomenclature on the device case as a proprietary device number and the date code.

It looks to me like it is a power bipolar transistor or possibly a field-effect transistor.

You can determine if it is a bipolar transistor and whether it is an NPN of PNP with a DVM that has a diode checking setting on it.

transistor testing using voltmeter

hgmjr

 

Using the methods you suggested and in the link below

http://www.allaboutcircuits.com/vol_3/chpt_4/3.html

I charted the results in the image below. It appears to be an NPN bipolar transistor.

 

So what is your next move now that you have a reasonable idea of what the devices are?

Is you goal to resurrect the circuit?

hgmjr

 

I'm trying to make a free-formed astable oscillator based on a basic schematic I found at techlib.com.

http://www.techlib.com/electronics/flipflopflash.htm

One red and one green LED makes for a catchy holiday feel.

I've made many in the past and part of the pleasure is figuring out how to make them for salvaged parts I suppose.

Here's an example. The device in the top of the picture uses a bicolor g/r LED. The one in the bottom doesn't work yet.

 

I can see you are having Tons-O-Fun.

hgmjr

 

Yes. Yes I am!

Here's a short quicktime video:

http://www.tcah.com/video/xmasLEDs.mov

Doc