RCA 7155 TO-66 package?

[JHow]

I am looking at a couple of transistors labelled "RCA 7155" that I can't find info about in my (admittedly old RCA manual) nor online.

Anyone have any info on what these are and what they could be replaced with?  It is NPN power transistor, but must be fairly low power, has about 17.5 DC volts from C to E.  They are in a Kalamazoo model 4, for which I don't have a schemo.  I found a Kalamazoo 3 schemo online which listed it as Motorola SJ 3405 or 3408 (I can't read the last digit).

The good news is, these work for now, but I am always curous if I had to replace something what I might use.

[gbono]

TO-66 packaged transistors are unobtainium. If you find a substitute that works, in that package, consider yourself lucky.

[tonyharker]

I would try the 2N3054 which should be still available.   The 7155 looks like a date code to me.  Future shows these available at $9.75 each here < http://www.futureelectronics.com/en/technologies/semiconductors/discretes/transistors/general-purpose-transistors/Pages/1397744-2N3054.aspx >

[J M Fahey]

Agree.
What I do in that case, is to replace them with TO220 cased ones.
Base and emitter leads , when carefully bent downwards fit in the original PCB holes, *one* screw will match the collector one, the other one will not be used or needed, you must use proper mica/grease and plastic insulators, of course.
If the original transistor is mounted away from the board, connected to it by 3 pieces of wire, the replacement is much easier, just cut and bend its legs so they become relatively short and firm stubs where you can safely solder those wires to.
I think TIP41 or TIP42 (NPN or PNP) will be good substitutes, if ever needed.
As a similar example, I have built over 8000 amplifiers with TO3 2N3055 transistors, along 40 years.
Had to stop using them because nowadays all available ones are counterfeit, and when I get one amp for repair (there are still thousands of them all over the place), I replace them with modern TO218 or TO247 plastic transistors, which as I said can be mounted in the same PCB with some judicious leg bending.
Yes, it's a point of pride for me to keep 20 or 30 years old workhorses still working as new.
It's also an excellent selling point.

[joecool85]

Yes, it's a point of pride for me to keep 20 or 30 years old workhorses still working as new.
It's also an excellent selling point.

I agree.   Too bad nothing like that is offered here in the US, just throw away garbage now.

[JHow]

Thanks guys!  Great info.  I have TIP41s on hand.  Fortunately, the orginals still work, so I'll levae those inplace until they die, I guess.

[JHow]

...I have built over 8000 amplifiers with TO3 2N3055 transistors, along 40 years.
Had to stop using them because nowadays all available ones are counterfeit...

Just a question about your comment about 2n3055s:  They still sell them at Radio Shack here (California) and places likes mouser... are those not real ones?

[J M Fahey]

Don't know about them firsthand, but I have been burnt so much by "reputable" dealers, that I had to switch to TIP142/147.
Suggest you read:
http://sound.westhost.com/counterfeit.htm
http://sound.westhost.com/fake/counterfeit-p3.htm
http://www.cdkands.com/counterfeits.html
and the Spanish page: http://transfal.tripod.com/
Another Spanish page suggests a "brute force" tester for hugh power transistors.
They either live or explode ... literally !!!
http://transfal.tripod.com/indexold.html
To have a small preview of what you will find there:
Original MJ15024/25 , notice the square chip size and the copper "coin" to which they are soldered, to better spread heat *inside* the case:

Now look at the counterfeits: much smaller square chips (which are the actual transistor, what you are paying for) and smaller or nonecistent copper coins.
The rightmost one has the chip soldered straight to the steel base, which is a very poor heat dissipator (seen any iron heatsinks lately?)

Tempering the problem a bit, maybe Mouser's are reasonably good (yes, there are "good fakes" too), would not trust Radio Shack that much, since it's not professional oriented.
And what do Peavey, Fender, Marshall, etc. do?
They buy straight from the manufacturer, impossible for us mere mortals.

[gbono]

I usually buy from Digikey - never had a problem in the last 2 years. I haven't done so but I would guess high current HFE is not going to be the same as original (large OEM die) and you could verify this with a TEK 576 or simialr (curve tracer).