Kustom 200B blowing fuses

[52 Bill]

I then saw I could just pull the sockets and test them without completely removing them, as they are isolated via the fitted wafer insulated washer, and plastic insulators for the screws.

I tried to tell you about the plugs on the E and B pins. I guess that I didn't make it clear, sorry.

Can someone suggest what I should purchase, and where, for the 36892 transistor. I'm assuming that exact one is not made anymore.

The output transistors were house numbered 2N3055 types. As R.G. suggests, you can use higher rated parts.

To test the drivers, do I need to remove them, or can I do the same type tests from the back of the board? Also, I'm assuming 38736 x 2 ,38737 x 2 , are the drivers . Why the different part #s?

You can test them in circuit, but there will be parallel paths, which will effect the readings. If you find some that are suspect, you may have to remove it to get a final test.

There are two different numbers, because there are two different transistors used as the drivers, one is an NPN and the other is a PNP. The standard numbers are 40409 and 40410. If you try and get NOS replacements, they will be fairly expensive. I have replaced them with more modern devices, but be careful as the pinouts may be different.

[R.G.]

Oh. If the drivers are the 40409/40410 types and are damaged, don't even try to get exact replacements. The combination TO-39 device and pressed on heat sink are unique. Count on using TO-220 devices and heat sinks, as well as perhaps wires on the board. It was common in layouts with the 404xx series to use the two mechanical support pins as extra collector pins for layout purposes. Suitable TO-220 replacements will be under US$0.50.

[Enzo]

Actually I still have a couple dozen NOS 40409/40410. They are in my storage unit, I'll see if I can find them. Pretty cool, they are RCA and still in the little individual boxes.

[R.G.]

Wow! They're still around! Neat.

I was expecting him to find a few on ebay for $50 each. I did a few amps early on with 40409/40410, and fixed a few others. The industry zoomed right past that kind of solution when TO-220s came into the market.

[J M Fahey]

Wow! They're still around! Neat.

I was expecting him to find a few on ebay for $50 each. I did a few amps early on with 40409/40410, and fixed a few others. The industry zoomed right past that kind of solution when TO-220s came into the market.

True, but TO220 were meant to replace TO66 , and there they did a thorough job, not one left.

[LarBal]

Haven't had a chance to test the drivers, but will these work for the outputs?https://www.newark.com/solid-state/m...o-3/dp/10P1534
I can't help but think I can find them cheaper. They were more expensive at Mouser, or obsolete.
52Bill, once i took the sockets and transistor apart, your suggestion made total sense, I just didn't realize they were in a socket at the time
R.G., yep from what I can tell they are in a TO-3 case
Enzo, if I find the drivers are faulty, I'd certainly appreciate those NOS parts!

[The Dude]

I haven't used those Solid State Inc. transistors before, but it seems like a legit company. Maybe someone else has experience with them. If not, I'd say give it a go.

[R.G.]

Yeah, give them a try. You're actuallyl buying Newark's assurance that these are quality devices. I trust Newark that much.

@juan:
Yeah, they were intended to replace TO-66s. I suspect that TO-126 and the UniWatt package were aimed at the TO-39. But the ability of the TO-220 to go down in power at a cheap price when paired with an aluminum channel heat sink likely killed off new designs with the TO-39. There are still a few types of 126 and UniWatt stuff being made, but my rationale is - why use them if they're not a lot cheaper and the TO-220 is higher power and likely to be tougher.

[vintagekiki]

I'm assuming 38736 x 2 ,38737 x 2 , are the drivers . Why the different part #s?

Underline
38736 is a NPN Si Transistor
38737 is a PNP Si Transistor

The K200B is an old-timer manufactured in the '70s. At that time there were no transistors that exist now.
If we want to keep as much of the original condition as possible, it would be best to use semiconductors from that era when repairing.
This is the least painful because the alterations are then the least.

Check all driver and power transistors with ohm meter¹⁾(range x1)
Faulty transistor can be open, leaky or shorted.

https://www.quora.com/How-do-you-identify-for-a-shorted-and-an-a-opened-transistor
How do you identify for a shorted and an a opened transistor?

http://120studio.com/tech/transistors.htm
Testing Transistors In-Circuit With a DMM

When replacing transistors, it is desirable that the replacements be from the same type family.
When replacing a transistor, match hfe in the limits +/- 10% and tested on the breakthrough voltage (min 100 V) The same goes for drivers transistors.

Each replacement driver or output transistor implies the setting of a quiet current (output) transistor.

Semiconductor Component Cross-reference Search
https://vetco.net/component-cross-reference

Equivalent replacement for the K200B

https://vetco.net/search/results?q=36892
https://vetco.net/products/2n3055-npn-si-transistor-60v-15a-nte130/nte130
36892 = 2N3055 NPN Si Transistor, 60V 15A - NTE130

https://vetco.net/search/results?q=38736
https://vetco.net/products/2n3053-npn-si-transistor-80v-1a-nte128/nte128
https://vetco.net/search/results?q=38869
38736 = 2N3053 NPN Si Transistor, 80V 1A - NTE128

https://vetco.net/search/results?q=38737
https://vetco.net/products/2n4037-pnp-si-transistor-80v-1a-nte129/nte129
https://vetco.net/search/results?q=38870
38737 = 2N4037 PNP Si Transistor, 80V 1A - NTE129

Edit:
In Circuit Transistor Tester
http://www.555-timer-circuits.com/transistor-tester.html

https://www.elprocus.com/simple-transistor-tester-circuit/

http://www.electronicecircuits.com/electronic-circuits/in-circuit-transistor-tester

¹⁾ Note on ohmmeter tests

(page 16-17)
http://www.cieri.net/Documenti/Schemi/Crown%20-%20Amplificatore%20DC300.pdf

The approximate values for measuring transistor resistance are shown below.
Large resistance means there will be little or no indication on Rx1 ohms scale. These values apply to transistor by itself outside the circuit.
For NPN transistor the first lead takes the positive meter probe. For PNP transistor the first lead takes the negative meter probe.

base-emitter low
emitter-base large
base-collector low
collector-base large
collector-emitter large
emitter- collector large