obsolete transistor replacement

Because the tab is connected to the ground pin internally. If you ground the tab then the pin is also grounded, bypassing the diode.

Yes. You'd need the whole heatsink 'kit', including the plastic insulating collar which goes on the bolt, or a plastic bolt.

Dave

We have original 2SB527 in stock for US$1.99 each.

Regards,

Glen Goodwin ACME Enterprises of Orlando

1-800-575-9833

Dave wrote:

Dave-

I agree with G for the most part. I prefer the 7912 approach rather then using the 7915. As someone else suggested, a capacitor from the output to ground would be a good idea. I think you mentioned having one in the original circuit.

Another alternative to the 7912 approach would be to use the negative version of an LM317 with pair of resistors instead of the one diode. One resistor would be connected from the regulator's output to its common ("adj") terminal. The other would be connected from the common terminal to ground. Values would be chosen to produce the required output voltage. The LM317 regulator actually has about 1.2 volts output plus the voltage dropped by the resistor to ground. I assume there is a negative version of the LM317, if you wanted to look further.

Of course an exact replacement transistor is the most sure-fire solution. If you were to use an alternative part, I suggest using one rated for at least the minimum hfe of the original part, or at least one having an actual (measured) hfe of that value or higher.

Fred

Holy sh#t, this site is a GOLDMINE! You sell transistors that haven't been made since 1975! Tons of them!

Thanks, it's in my bookmark file. I already bought a TIP42C (over-rated, but at $1.99 the price was right) at my local electronics store. BTW, how much is shipping to Canada?

Looks like you're getting lots of help Dave. The comment about insulating the tab is so that you DON'T negate the effect of adding the diode. The tab is common with the ground pin so you'd be bypassing what you'd be trying to accomplish :)

Gord

(snip)

Sorry to be a spolier, but according to my data sheets the tab is connected to pin 2 (whic is INPUT on a 7912 and presumably on other 79XX regulators). So the O/P is going to have to go the insulated mounting route regardless of the diode.

Howdy Budgie....right you are.....thats not being a spoiler but just being helpful :). Must admit I based my experience has been with the positive VR's (obvious eh!). Having said that......the tab of a

79xx wouldn't necessarily need to be insulated but it has to be kept in mind for sure. (anyone here ever tried building their regulator into a grounded side of a rectifier heheh......it works just fine - just looks disconcerting when you look at the diagram).

component,

Well I went with a TIP42C, over-rated (6A vs. the 0.8A I am replacing AND that's probably over-engineered) but available locally. I don't have any mica insulators or plastic screws and they are an hour drive (or $15 shipping) away.

Thanks for everyone's help, I learned a great deal. BTW, I threw the new PNP into my DMM's transistor testor and it came up with an hFE of 390. I am thinking that this is a fairly useless number other than to show that the transistor is functional as the hFE measurement will vary greatly with input current. Wonder what the old one would weigh in at? Interestingly checking the old transistor with a multimeter showed perfectly normal behavior, B-E conducted one way only, B-C conducted one way only, C-E did not conduct. But it didn't work in my transistor tester, came up 000 for hFE.

Again, thanks for the assistance.

Dave

I still don't know where you got that spec. What was the manufacturer of that obsolete unit.

You really need sets of curves to get a real indication of things. I have mostly tested them out with an analog ohmeter, my favorite. Sometimes you will see extra leakage on CE or other terminals when they are bad. I have not tested a bad unit with the diode test function, which should indicate some voltage drop across CE. greg

Glad you like it, Dave! We carry a lot of "new old stock" items, as well as the "latest and greatest."

Shipping to Canada is the same as anywhere else, and shows up in the shopping cart as you add items. (BTW we ship to Canada every day).

Orders over US$50.00 - FREE shipping and handling Orders US$20.01 to US$50.00 - S & H = US$6.99 Orders US$10.00 to US$20.00 - S & H = US$8.49 Orders unders US$10.00 - S & H = US$11.99

For orders under US$50.00 a small additional charge will be added for flybacks.

Typically we use US Postal Service Global Priority Mail to Canada, which arrives in about 4-7 days.

If you need more information please call us toll-free at

1-800-575-9833 (USA and Canada) or 1-407-296-2333.

Glen Goodwin ACME Enterprises of Orlando

that

translated directly from Japanese:

I'll have a look at the part and get the manufacturer.

am

input

checking

B-E

Taken from my Towers 1980 edition databook, the main difference is the packge type, clearly a TO126 as the replacement shows2sb631 http://www.ortodoxism.ro/datasheets/sanyo/ds_pdf_e/2SB631K.pdf The max current spec does vary among the bunch.

I have about 8 different replacement numbers as I have gone through all this.

greg