Need Transistor Sub For Kustom K200

[earache]

I replaced a noisy transistor on a Kustom K200-B not so long ago (with help from many members of this forum - Thanks Again!). Anyway, since then although the amp is not noisy it is not as loud as it was. The transistor I replaced was a SE4002 transistor which I replaced with a 2N2222.

I have since put the old transistor back in and the amp is loud again (and noisy again - it hisses!). I need an NPN transistor that has higher output than a 2N2222. What do you guys suggest for a sub that's not an NTE part?

[Mark Black]

Sparse info I have on SE4002:

NPN
Vceo = 25V
hfe = 200-1000 @ 0.1mA

From that it looks like a 2N5088 or 2N5089 would work, among probably many other relatively high-hfe TO-92 types.

Both available at Mouser for cheap.

Good luck!

[Iceviper]

My Linear databook lists the 2N2222 as having the following: Vcbo=60v, Vceo=30v, Vebo=5v, Icbo=10na @50v, hfe between 30 & 110 depending on Ic and Vce and an ft of 250 mhz @ 20ma Ic. Try the 2N5088 or the 2N5089, as suggested above, they are pretty close (actually better). If you don't mind my asking, why not NTE?

[earache]

I have read many times on this and other forums that NTE replacements are often just ballpark replacements, specification-wise.

They are more expensive also. I suppose that if there isn't a one-to-one replacement then NTE is all that's left.

[Iceviper]

It might be a good idea to check the specs for the NTE suggested replacement against the above. If they are equal or better, and not extremely expensive, why not? Mouser might be a good try for the above suggested replacement and Newark still lists the 2N2222A (made by Multicomp) for under a dollar (just a suggestion).

[Enzo]

Those 5088/5089 sound OK to me too. Or even MPS8097 or MPSA18 or even 2N5210.

NTE crosses the 2N5088 to their 123AP - which is their all purpose general use NPN signal transistor. the 5088 is a low noise type, the 123AP doesn't show a noise figure in its data sheet that I can spot.

Mouser sells the 2N5088 for 7 cents each, and the NTE 123AP for $1.25 each

And that pretty much tells the tale on NTE.

If you are in a hurry, and a local store stocks NTE, sure, why not? But if you are ordering anything, then I can see no reason to order anything but the real parts.

[jrfrond]

I have both the SE4002 (by attrition) as well as 2N5088 in stock (hundreds of them!) and the 2N5088, as a low-noise, hi-gain transistor, works just fine as a sub.

[earache]

Thanks To All

Thanks to everyone above for their input, I'll search out some 2N5088 or 2N5089's and make the change. After the sub I'll post the results for sake of completion of this thread.

[earache]

Back At The Kustom

Well, I've ordered and received some 2N5089 transistors to replace the SE4002 transistor that has been a problem. The amp is still not as loud as it should be and it distorts from about half volume on up.

Some of my previous trouble is self induced, I'm afraid. The transistor I replaced is an odd-ball early TO-106 package - it's got a rounded "plastic bead" look to it with only a very small flat on it's periphery. When I have been swapping in common TO-92 types I have been putting them in "backwards", with the emitter and collector swapped. I have that problem figured out now. Funny how it would still pass sound though...just not much.

So I left this beast for a little while and now I'm back trying things again. I went round the transistors on the main board (PC703) and took voltage readings as listed on the attached schematic

There are a few voltage readings that ldon't look right.

Transistor****Expected Voltage(s)****Measured Voltage(s)
Q701********-32.4 +.6************-26.6 +.67
Q702********-31.8****************-26.4 +.67
Q703********-32.4 -33. -3.7*******-27.2 -26.2 -9.5
Q706********+1.2 +1.*************+1.15 +.01
Q713********+9.32 +.51************+9.24 +8.07 +8.12

I'm afraid I sometimes have trouble trying to sort out the relationships between parts as shown on a schematic - pure inexperience I guess. Could someone take a look at the attached schematic and point me to some possible root causes?

TIA

[Enzo]

I think that +0.51 at the base of Q713 is a typo. I might believe 8.51.

[earache]

Kustom Fixed!

It's with great relief I can post that this amp is finally fixed. I went around the board testing some of the resistors and while replacing some of the out-of-spec ones, I found where I had caused a solder bridge. It likely happened when I was touching up solder joints previously.

The solder bridge was knocking down the -39.5V power to the Q701, Q702 and Q703 resistors.

You are correct Enzo, the +.51V at Q713 was a typo. Thanks for your help.

This thing is now LOUD AS HELL and without distortion! Whoohoo! I've been fiddling with this amp off-and-on for 4 months...but I am a MUCH better troubleshooter because of it.