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K 100-2 Transistors [message #6068]

Wed, 10 August 2005 19:41

butler
Messages: 7
Registered: August 2005

Junior Member

Hey Kustom klan,

I have been to this sight several times and have found it to be very informative to say the least. I Want to thank every one for their knowledge of Kustom products. I have had this amp since 1978 and it still works great, except the reverb(trying to fix it now). It is the one with the plexi front panel and the spkr cab is slightly slanted with brushed aluminum ports, inside and out. Blue speckled tuck and roll! Okay; to my need for help: I am looking for the replacement Transistor for my K 100-2 combo. This Transistor does not seem to be able to cross in any reference book I have looked in, so any thoughts would be greatly appreciated. The PC board that I have in the head is labeled PC 104. The markins on the transistors read "PET8002" or "81-825", This transistors is Q105. The other Transistors are "PET8002" or "81-821" Theses are Q103,Q106,Q108,Q109,Q110,Q112,Q113,Q120.I have the schematic for this model (or atleast the newer version with some changes).On the schematic, the number says "form 1006 Rev 4, 1-70". This schematic has a transistor labeled Q131, which I do not have on my board, and many resistor values are different. Would anyone have the older form of this schematic with the correct values and Q131 omitted?

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Re: K 100-2 Transistors [message #6074 is a reply to message #6068]

Thu, 11 August 2005 12:54

stevem
Messages: 4775
Registered: June 2004
Location: NY

Senior Member

Hi, pet8002 crosses to a very common npn transistor, I have my info at home and will post it for you on friday.also kustom had many revisions on boards, so after the boards part number it would say rev-1 or what ever.

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Re: K 100-2 Transistors [message #6076 is a reply to message #6074]

Thu, 11 August 2005 15:42

butler
Messages: 7
Registered: August 2005

Junior Member

Thanks for the reply,

The transistors have two different numbers on them even though they both say "pet8002" one has 81-825 and the other has 81-821. Don't know if that part matters. Also my board just says, "KE1-1 PC 104". Looks like this is the original board before any revisions. I was curious what the function of Q 131 has on the system. Hooking up my reverb tank seems to eliminate any gain as I increase the intensity and a louder hum comes from this increase also. When I bump it, the springs do make a crashing sound from the speakers, which is normal, but I have no reverb to speak of. Any ideas?

Thanks for the help

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Re: K 100-2 Transistors [message #6086 is a reply to message #6076]

Fri, 12 August 2005 12:43

chicagobill
Messages: 2006
Registered: April 2003

Senior Member

Welcome to the board!

The PET8002 or SE4002 transistor is as Steve noted, a NPN Silicon transistor, and can be replaced with almost any reasonable quality unit. My cross-references suggest a ECG123A or ECG123AP transistor. Due to the minimal voltages that Kustom pre-amps use, I would think that a common variety 2N3904 will work as well. The second number 81-821/825 I believe to be date codes, and can be ignored.

At least 90% of all reverb problems in Hammond type tank systems are mechanical in nature. The first thing that I always check for are bad cables or connections. Then I check the wires inside the tank that connect the transducers to the RCA jacks. If you have access to an ohmmeter, check the resistance at both input and output RCA jacks. You should read about 180-200 ohms across either jack. From your description of crashing sounds from the speaker, your output transducer wires are OK. If you don't have an ohmmeter, you can check the input transducer wiring by plugging the "output" cable into the "input" jack and with the amp turned on, carefully shaking the tank. If you hear crashing through the speaker then your input wires are OK and the problem is somewhere in the input cable or the circuitry. Some Kustom reverb input cables are intentionally not shielded/grounded, so don't worry if yours isn't.

Now for the safety message: Working on any amp, plugged in or not, can lead to potentially leathal situations. Never work on any amp beyond your training or expertise! Serious damage can be done to yourself and or your amp.

Bill

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Re: K 100-2 Transistors [message #6088 is a reply to message #6086]

Sat, 13 August 2005 10:25

butler
Messages: 7
Registered: August 2005

Junior Member

Smile

Thanks Bill,

I appreciate your input Bill, I will replace the transistors in question with your suggestion of the ECG 123. The question of Q131 is still puzzling me though; I seem to believe that this has something to due with the inop of my reverb tank. Would you happen to know where I could get my hands on an early version of the schematic for this head? It is hard to trouble shoot with a schematic with so many changes! Also, thanks for the interest in safety. I am A licensed electrician and an electronic hobbiest and have repaired numerous electronic equipment so I understand where you are coming from. I love to work on old amps for fun Smile

Smile

Thanks Again
MIKE

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Re: K 100-2 Transistors [message #6095 is a reply to message #6088]

Mon, 15 August 2005 16:40

chicagobill
Messages: 2006
Registered: April 2003

Senior Member

Mike:
Sorry, I don't have any schematics for your amp. Have you tried the source here on the board? Even if it is not listed yet, maybe they have access to one.
Bill

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Re: K 100-2 Transistors [message #6097 is a reply to message #6068]

Tue, 16 August 2005 07:41

stevem
Messages: 4775
Registered: June 2004
Location: NY

Senior Member

I will look at my schematics tonight, I think my pc104 is only rev-1.

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Re: K 100-2 Transistors [message #6100 is a reply to message #6068]

Wed, 17 August 2005 07:55

stevem
Messages: 4775
Registered: June 2004
Location: NY

Senior Member

I looked last night, and I do not have a 104 layout.Sorry!

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Re: K 100-2 Transistors [message #6102 is a reply to message #6068]

Mon, 22 August 2005 09:08

Wattsyurz
Messages: 16
Registered: July 2005
Location: SC

Junior Member

I agree with Bill, the problem is probably in the tank, not the head. Anyways, if you've always owned this, the reverb must have worked w/o the mysterious transistor. If all else fails, FX pedal?

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Re: K 100-2 Transistors [message #6108 is a reply to message #6102]

Wed, 24 August 2005 20:49

butler
Messages: 7
Registered: August 2005

Junior Member

Thanks for the thoughts,

One problem though; even when i take out the reverb tank and turn the reverb control up, i loose all gain of the amp( the farther i turn it up, the more gain i loose). With the reverb tank in and i turn up the reverb control, i get tramendous feed-back and the output decreases the same as if it were out.This makes me believe that it is something in the board. I have changed some components, but the problem still persists. Any other ideas?
Thanks for the advice
Mike

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Re: K 100-2 Transistors [message #6109 is a reply to message #6108]

Thu, 25 August 2005 11:26

chicagobill
Messages: 2006
Registered: April 2003

Senior Member

Mike:
By feedback do you mean oscillation? Does the amp whistle as you turn up the control?
Bill

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Re: K 100-2 Transistors [message #6111 is a reply to message #6109]

Thu, 25 August 2005 22:17

butler
Messages: 7
Registered: August 2005

Junior Member

ok, lets see if i can explain this alittle better to you. By feedback i mean that it acts as a sustain would act. once i turn the reverb on the feedback starts out low but it continues to become louder and louder over a short period of time.(This only happens when the reverb is connected). If the reverb is taken out of the system, I don't get the "feedback" but by turning the reverb up, it causes a depletion of volume or gain. I guess you could call it oscillation but to me it is the same thing you would get if you stood in front of the amp holding a note on your guitar for a long time and it would start to squeel. I am not sure if i am explaining this in its simplest terms but i hope you get the idea.

Thanks for your input
Mike

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Re: K 100-2 Transistors [message #6117 is a reply to message #6111]

Fri, 26 August 2005 17:50

chicagobill
Messages: 2006
Registered: April 2003

Senior Member

Mike:
If I understand what you are describing, the feedback is the sound of the reverb tank feeding back. When you unplug the tank and turn up the reverb control, the loss of normal signal volume is probably normal. Some Kustom designs use the Reverb control as a balance control between normal signal and reverb signal. Full counter-clockwise = all normal signal, full clockwise = all reverb signal.

Try moving the speaker away from the amp head and see if the feedback stops or lessens when you turn up the control. I don't know if the tank is original to the amp, or if it has been replaced with the wrong type. You may need to replace it with the correct one, and or insulate it better to stop the howling.

If your reverb sound is still weak, then your problem lies in the input/drive section of the circuit. If your tank was replaced with a Fender type tank, this would cause the reverb to be weaker than normal, due to the fact that the input impedance of the Fender tank is too low to operate in the Kustom circuit.

Bill

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Re: K 100-2 Transistors [message #6118 is a reply to message #6068]

Sat, 27 August 2005 13:37

butler
Messages: 7
Registered: August 2005

Junior Member

cudos Bill,
As you mention it, the reverb tank is a replacement tank, but i got it from a guy out of ohio(as i recall) that supposably was a kustom dealer( I also obtained the schematic from him at the time). any way, I assumed i had the right reverb tank but i will run it by you to see what you think. The tank is a "accutronics", part # 4FB2CIA. It is 17 inches long with dual springs ( 4 total springs, two rows with two tied together in the middle) Not sure what the impedence is on this unit.Could you tell me if this is and exceptable replacement?

Thanks again
Mike

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Re: K 100-2 Transistors [message #6122 is a reply to message #6068]

Mon, 29 August 2005 14:05

chicagobill
Messages: 2006
Registered: April 2003

Senior Member

Mike:
Impedance wise, the 4FB2C1A reverb tank, should work in your amp. The input impedance is rated at 1475 ohms.

The only thing that I'm not sure of is, if the input jack on the tank is correct or not for your amp. Your tank has an insulated input jack, meaning that the ground of the input jack is not connected to the metal case of the tank. If your amp needs an non-insulated input jack, the ground connection of one of the cables at the circuit board may not be connected. Check to see if the cable shield from the circuit board to the input of the tank is connected to ground at the circuit board. If it isn't, try jumpering the tank input jack ground connection to the metal case of the tank.

Also, don't forget to check the cables, as well as the plugs and jacks for corrosion.

Bill

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Re: K 100-2 Transistors [message #6138 is a reply to message #6122]

Wed, 07 September 2005 15:47

butler
Messages: 7
Registered: August 2005

Junior Member

Thanks Bill Razz

Razz

Once again you have hit the nail on the head with your comments. Grounding the input side of the reverb tank fixed the problem and it seems to be working fine. As the schematic shows NOT to ground the input side of the shield, I was not inclined to even attempt it, but by grounding it, it came to life. Thanks again for all your help. If I ever run into another problem I will know who to contact.

Forever grateful
Mike

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Re: K 100-2 Transistors [message #6139 is a reply to message #6068]

Thu, 08 September 2005 11:52

chicagobill
Messages: 2006
Registered: April 2003

Senior Member

Mike:
Great news! I'm happy to hear that you got it working.

Sometimes it's the small things that we overlook that turn out to be the cause of the problems.

I'm glad to have been able to help.

Bill

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