2n6426 sub?

[lowell]

Got a Mesa Stilleto in here. Had some switching issues. I need to replace a 2n6426 darlington PNP, but don't have any on hand. Here's a datasheet:

http://www.mouser.com/ds/2/68/lssgp074-41231.pdf

Here's a schematic and the circuit is on the last page in the "mute" section. I believe all this transistor does is turn 2 jfets on and off, so not much current being pulled from it. Can I use a standard transistor for this or do I need a darlington? I have MPSA14 in stock but it seems to be a little underrated. I have 2n3904, 2n5088 and many others. Thoughts? Thanks!

http://music-electronics-forum.com/a...4-stiletto.pdf

[The Dude]

It is an NPN- not PNP, but when you reference substitutes, you referenced NPN's, so I think maybe it was just a slip.
Anyway, the MPSA14 is similar enough with the exception of the lower collector voltage rating (30V). However, the circuit runs off of only 12V, so I see no reason you couldn't substitute.

[lowell]

well that's just like....your opinion man.

You're right it was a slip. Ok cool thanks! I'll give it a shot. So the Vc/e is a max? I got the impression it was a Min. Datasheet is a bit unclear with the abbreviations. But yah being that the original npn said 40v I guess I shoulda known.

[Enzo]

The transistor number isn't critical, any little darlington with enough voltage and current rating should work. However i am concerned a bit. You said not much current would be drawn through it. True, but that is not what darlington is about. Darlington is about the gain. A plain old trsansistor can handle tons of current, look at the typical output transistor. But the signal at the base has to turn it on. So if for example the output of some little logic chip has to turn a bulb off and on, then it might need a darlington for the small logic signal to drive the transistor.

Voltage ratings are like voltage ratings on any other component, a maximum. A 40v transistor means don't put 100v across it. The mute has to work from a little "mute pulse", so you want it to snap to quickly. You don't want it to decide how fast to move on the basis of current. A hair trigger, so to speak.

[lowell]

Thanks! Good info. So a tiny mute pulse signal needs to be applied to a transistor with a large gain. I get that. So if the +10v reaching the jfet pnp (on fx send tube gate) gate needs to be brought down say, to 0v, that would require the ratio of the drain/base voltage to be quite large. Sorry that's probably not the most eloquent description. But I'm trying to convey that I get it, via an unintentional filibuster.

[J M Fahey]

If they used a darlington there, you need a darlington.
Order a proper one, meaning: same polarity, some 20 or 30 Vce , not sure about relay current, it should be able to handle twice as much at least to have some safety margin, and of course, be a darlington.
IF not available (search not a written substitution but any part which meets the parameters) kludge one out of 2 discrete transistors.

[gbono]

The 2N6426 is obsolete that's the bad news - the good news is Arrow has stock 2N6426G for ON Semiconductor | Arrow Electronics Components It's sad to see the TO-92 package go away

[nickb]

The 2N6426 is obsolete that's the bad news - the good news is Arrow has stock 2N6426G for ON Semiconductor | Arrow Electronics Components It's sad to see the TO-92 package go away

Just so's ya know - the 2N6426 has an Ic(max) of 1.2A the 2N6426G is 0.5A - not that I expect it will matter for a small relay.

[Enzo]

I'd challenge that. 1.2A in a TO92? On Semi (Moto) uses G on the end to mean green, as in lead free. The lead in them is tinning on leads and stuff, I don;t think there is any on the silicon, I could be wrong. I would suspect 1.2A is a typo. I found a number of brands of the part, all are 500ma or 450ma.

[nickb]

I'd challenge that. 1.2A in a TO92? On Semi (Moto) uses G on the end to mean green, as in lead free. The lead in them is tinning on leads and stuff, I don;t think there is any on the silicon, I could be wrong. I would suspect 1.2A is a typo. I found a number of brands of the part, all are 500ma or 450ma.

It seems the vary with the manufacturer. Fairchild's ( now part of on) is 1.2A:
2n6426.pdf

[The Dude]

FWIW: I was looking at these 2 datasheets.

http://www.onsemi.com/pub_link/Collateral/2N6426-D.PDF

http://www.onsemi.com/pub_link/Collateral/MPSA13-D.PDF

Both are darlingtons and both spec pretty much the same with the exception of Vceo nd Vcbo. Since the circuit in question here has a supply of 12V, I see no reason the MPSA14 wouldn't be a good substitute.

[gbono]

MPSA14 also discontinued 2006 try MPSA13 or KSP13BU - old Motorola data book has 2N6426/7 as IC - continuous 500mA. Since this is/was a JEDEC standard part I believe IC=500mA was how the part was registered. Details, details, details.....

G=RoHS compliant for On Semiconductor products

Lead was only used on lead frames never in the processing of the die (it would be a contaminant).

[The Dude]

......I have MPSA14 in stock......

He has MPSA14 in stock.

[lowell]

This is amp has become a nightmare. As I tried to work out the hum issue, I made a mistake with my meter and mistakenly touched the filament (ac) to the B+.. .had my meter set to "continuity." Whoops. I then had very little sound....found that J175 was shorted, and 6426-P was faulty...replaced both (6426 with MPSA14). This brought me back to where I was. Which is that the Clean Crunch mode is just WAY too loud, OR the other 2 clean modes are too soft. I'm not sure as I have no reference. Yes Mesa said this is normal, but I swear it's even more so now after the little mistake I made, which I believe is fixed.

The other 2 modes sound very dark, bass heavy, and the tone controls do very little. It's the opposite with the Crunch mode, it's way loud, brittle, lacks low end, and the tone controls do very little.

CH2 is somewhat similar. Tight Gain is way loud, brittle. Other 2 modes are dark and low volume. I emailed mesa with all this info asking for some assistance. I'm just getting weary of this amp. Been solid on it for probably 20hrs+. I just need to set it aside for a few days and come back with fresh eyes.

[Enzo]

YES YES YES. If you are going around and around in your head, getting nowhere. STOP. Do something else, come back another time with a fresh outlook.