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How Hard Is It Anyway/ [message #13478]

Tue, 27 April 2010 15:38

noexit
Messages: 21
Registered: February 2008
Location: Far North

Junior Member

I have a couple of K100-1's that have been giving me a lot of problems. I have had them both in to the only tech I know around these parts. He kept them for several months and did some stuff, but they still ain't right. One of them farts every time I hit a "D" with my bass. The other one sounds good for a few minutes then it starts to distort and lose volume till it's silent. I think it's a heat thing because it lasts a bit longer if I take it out of the box.
I also have a K100-2 that has issues with the reverb and the trem. The reverb is so grand canyon that you can hardly use it and the trem has very little presence even when cranked.
I would like to change them all to 3 prong plugs and do a few more mods as well such as maybe changing the transformer to a toroidal type. The thing is, I don't have to much experience with electronics other than simple soldering repairs but I do know how to do some stuff and understand other stuff.
Bottom line is I would like to use these amps when I play gigs but they have to be dependable. So where do I start? When I say start,I mean to say, what kind of gear should I buy to get started?

350!

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Re: How Hard Is It Anyway/ [message #13481 is a reply to message #13478]

Wed, 28 April 2010 05:57

stevem
Messages: 4733
Registered: June 2004
Location: NY

Senior Member

Non of the problems you have discribed with any of you K100s should be hard to fix for someone ( IE tech) who knows what they are doing!

In regards to the amp that you say is farting our I would have to say that its one of two things.

The first being a bad solder connection on the boards, a or a bad connection in regards to one of the slip on connections on one of the two output transistors, and these problems would be more of a issue on a non- piggy back amp/combo for bass due to the added vibration they get hit with.

The other problem with the amp could be its just in need of having the two big 50 volt at 2500 mfd power supply filters mounted on the floor of the amp replaced.

The second amp sounds like it has a bias problem in the output stage.
This could be due to the something as simple as the bais tracking diode that mounts in a clip inbetween the two output transisors being out of its clip, or it is the case sometimes due to vibration for one of its stiff brass like wires to snap off.
The problem could also be due to someone replacing one of its two output transistors during a repair session with a new one that is way way out of match range to the other.

The reverb problem is most likly do to having the wrong replacement pan in the amp, its tremolo problem I would say would take a Tech to trace out, but I guess we could help you step thru it little by little.

Is this reverb/trem problem in a K100 combo amp, or head as the circiut boards are different?

[Updated on: Wed, 28 April 2010 05:59]

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Re: How Hard Is It Anyway/ [message #13485 is a reply to message #13481]

Wed, 28 April 2010 10:54

noexit
Messages: 21
Registered: February 2008
Location: Far North

Junior Member

All 3 are heads. I have the schematics for both heads and my tech walked me through the trem and showed me what it probably is. He's a pretty good guy and has been working on these old amps pretty much since they were new. Problem is, I live 5 hours away from him and he will keep them for months as he is really busy.
I will have a look at the work order to see what he did exactly. They both worked good for a while after I got them back.
How can I tell if its the right or wrong reverb pan?

350!

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Re: How Hard Is It Anyway/ [message #13486 is a reply to message #13478]

Wed, 28 April 2010 11:09

stevem
Messages: 4733
Registered: June 2004
Location: NY

Senior Member

You need an ohm meter to check the resistance across the input and output RCA jacks respectivly.
They should check in at 175 to 200 ohms if its the right pan.

Also the input jack of the pan should not be grounded to the case of the pan, but the output jack should.

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Re: How Hard Is It Anyway/ [message #13487 is a reply to message #13478]

Wed, 28 April 2010 11:54

chicagobill
Messages: 2005
Registered: April 2003

Senior Member

I believe that the reverb pan on a K100-2 head should have the input and output connectors grounded.

If you have too much reverb, it may be a replacement tank with a longer than normal delay or maybe a three spring model. I've also seen a few tanks that were just really efficient and worked a little too well.

Are there any codes rubber stamped on the tank?

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Re: How Hard Is It Anyway/ [message #13488 is a reply to message #13478]

Wed, 28 April 2010 11:58

stevem
Messages: 4733
Registered: June 2004
Location: NY

Senior Member

I was not remembering it clearly so I pulled out my PC1500 layout and the input is not shown as being grounded, yet now as I dig out my test notes I have it marked as being grounded for both the K100s and 200s.

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Re: How Hard Is It Anyway/ [message #14666 is a reply to message #13478]

Fri, 29 October 2010 20:02

noexit
Messages: 21
Registered: February 2008
Location: Far North

Junior Member

Kinda got busy this year. Ok, so I was messing with the k100-1 head and cab. What it does is, while playing, a loud hum starts creeping up from very quiet to loud and at the same time the volume of the instrument starts to break up and disappear. It seems that the louder I have the volume, the faster it happens. If I turn the amp on and off, the hum goes away, but comes back quickly. Any ideas?

350!

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Re: How Hard Is It Anyway/ [message #14667 is a reply to message #14666]

Fri, 29 October 2010 20:48

pleat
Messages: 1452
Registered: June 2004
Location: Belding, Mi

Senior Member

quite a gap between April and October. From reading the other posts. you have Two K100-1 two channel heads, and one K100-2 single channel reverb/trem head.
The heating up and shutting down. Are you running a 8 Ohm cabinet to the head? The K100 piggyback amps want a 8 ohm load. Running a 4 ohm will heat the amp and may shut down.
PC103 the reverb model, there were some changes made, so you may have a K100-2 head that the mods weren't done after the amp was in the field.
The canyon reverb, to help turn down the reverb you need to short out Resistor 172.
The other mod that came out in the PC104 non reverb head. R184 may have a 4700 ohm resistor, it needs to change to 470 ohms. The other modification, Q126 and Q127 need to have a heat sink installed.

The reverb tanks are original Gibbs Type C 175-185 ohms input and output.
I'm not a tech, just reading off my Dealer update sheet that was sent to dealers after they learned of problems in the field.
pleat

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Re: How Hard Is It Anyway/ [message #14669 is a reply to message #14667]

Fri, 29 October 2010 22:04

noexit
Messages: 21
Registered: February 2008
Location: Far North

Junior Member

Like I said, I got pretty busy this year. Both of the K100-1's have 2x12 cts cabs. The head does the same thing plugged into either cab. I haven't even looked at the K100-2 in ages. I moved into a smaller place and it's packed away right now.

350!

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