Passbank Transistors

[alwin]

Hi all freaks,<p>About the replacement of all 44 2N3055 PNP transistors of a Spectra Physics 265 exiter:<p>Do they have to be matched in terms of Hfe or not?
If so, how should I match them together?
Which replacement should be used :2N3055 or 2N3055H ?<p>All replies are welcome!!<p>Tanx
Alwin <img src="graemlins/cry.gif" border="0" alt="[Cry]" />

[wler]

Well,
no one answers and I shouldn't too, but just in order that somebody says something,
I'll give some comments despite I cannot give a clearcut answer to your question.<p>Just for the record, 2N3055 is NPN and not PNP; the H version has higher voltage but less Ptot, if I remember right; to decide what to take would require to know the details of the circuit.
At any rate, if there are "sufficiently high"
emitter resistors, then matching hfe is not important, otherwise it might be necessay - again, hard to decide without plan.
If you want to match hfe, get a batch of them
(they are cheap) and replace all of them so that all are from the same lot. On top of that you may easily measure hfe, since many if not most cheap multimeters have hfe measurement built-in; then just take those whose hfe matches best. But I would guess it won't be necessary<p>You can also check via the emitter resitors whether your choice of T's balance the current well ot not, and replace those which use much more or less current than the average.

[andi]

Hello Alwin<p>it will be the standard 2N3055. It is the best to buy all 44 from the same lot. I never have matched the 3055 together, the 22 strings (2 x 3055 in series) have all a 1ohm emitter resistor in series. Often i only replace the transistors of burned strings. And check the 22 pcs. 2A fuses from the strings.<p>Andi

[alwin]

Thank you both<p>Of course the 3055 are NPN (stupid of me!!)
In the meantime, I've measured the Hfe's of
an other passbank with a multimeter, but these transistors transistors weren't matched at all. (5<Hfe<50). wich seemed weird to me.<p>@ HB they said the it should be enough to take
all of them from te same batch, just as you recommended me:-)
So I've placed an order @ farnell for
100 x 2N3055 and 100 fuses..........
hope that helps.<p>tanx again..<p>Alwin

[alwin]

yahoooow,

The Spectra PSU, funktioniert again!!

greetz
Alwin Argon &Co

[andi]

Alwin

gratulations...

i hope i never have to repair this one

[img]http://www.laserundlicht.de/Arrowsound/ ... "0"%20alt="[/img]

this is the passbank of the 270 PSU, used for SP171 lasers (big brother of the 265).

Andi