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k200b-3 questions [message #11684] Fri, 28 August 2009 13:05 Go to next message
jccoombs is currently offline  jccoombs
Messages: 2
Registered: August 2009
Junior Member
Hi, I'm new to the board and to Kustom amps. I recently purchased a K200B-3 serial# 27081 with matching 2x15 cab. I purchased the head understanding it had some issues, mainly channel 2 was not functioning, the pilot bulb and lens was missing, and channel 1 had filthy pots and had some static. I opened up the amp when I got home and it was extremely dirty so I cleaned the pots and attempted to clean the dust out. It seemed to sound somewhat cleaner but still nothing from the second channel. In trying to work the second channel I noticed that working the selective boost knobs produces extremely loud pops. I left it at that yesterday and didn't mess with it anymore. Today I was playing through the first channel for maybe five minutes and the sound cut out and I was left with a loud, steady hum, almost like a shorted speaker. I ran another head through the cab and it sounded fine albeit a bit buzzy. I opened up the k200 and reconnected the cab and noticed a spark. My questions:
1) What could cause the sudden failure of the first channel?
2) Channel 2 seems like a bad input jack but what would cause the popping on the boost?
3) Does the missing lamp cause any issues other than appearance?
4) could the buzz in the cab be from a dirty jack? its noticeable across the full range and the speakers otherwise sound loud and full.
5) Am i correct that this cab would be 8ohm? the only markings are kustom by ross on the front and altec on the back plate.

Sorry for the long post and thank you for any help
Re: k200b-3 questions [message #11688 is a reply to message #11684] Sat, 29 August 2009 00:17 Go to previous messageGo to next message
oren hudson is currently offline  oren hudson
Messages: 256
Registered: March 2008
Location: Gastonia, NC
Senior Member
I can't help you with your problems, but did want to welcome you to the forum. Lots of knowledgeable folks on her willing to help. So, good luck. Cool
Re: k200b-3 questions [message #11692 is a reply to message #11688] Sat, 29 August 2009 11:34 Go to previous messageGo to next message
pleat is currently offline  pleat
Messages: 1408
Registered: June 2004
Location: Belding, Mi
Senior Member
Again, Welcome to the site. I'm not a tech but to help some of the other techs, they will first need to know what color your kustom is. LOL. You may want to state the channels as left and right channels. On your -3 head, left channel should be a straight volume, bass, treble, and bright switch. The right channel is the channel that has the selective boost and harmonic clipper. First off, if the amp is giving a loud hum, Seeing a voltage spark when you plug in the speaker leads me to think you have some serious issues with the power amp section, and may be pumping DC Voltage into your speakers and can fry them. Again I'm no tech and it may be AC Voltage, but I do know you can cook your speakers.
The popping sound when rotating the selective boost switch, is a issue that most have. In the few dash 4 heads I've owned they all did it, even after cleaning the 7 position switch. I really think you need to have a qualified tech take the amp and get the power amp working and then have him chase down why the pre amps are not working like they should. In any amps I have if I can't get something cleared up with some contact cleaner, I just take them to my repair guy and have him go through the complete amp.
Nothing worse that have the amp fail on a gig.
Don
Re: k200b-3 questions [message #11693 is a reply to message #11692] Sat, 29 August 2009 11:41 Go to previous messageGo to next message
pleat is currently offline  pleat
Messages: 1408
Registered: June 2004
Location: Belding, Mi
Senior Member
I forgot to answer your other questions, the 2x15 cabinet is 8 ohms, two 16 ohms speakers wired in parallel. Given the fact that they are indeed original speakers to the cabinet. After almost 40 years, a lot can happen, speakers blown and re coned with the wrong impedance. Original speakers removed and cheap replacements installed. Your jack plate says Altec but without pulling the back off, and actually making sure what's in the cabinet. A dirty speaker jack would not case a buzz, I think the amp has damaged the voice coils. A dirty jack would cause the cabinet to work or not work.
Don
Re: k200b-3 questions [message #11695 is a reply to message #11684] Sat, 29 August 2009 14:55 Go to previous messageGo to next message
chicagobill
Messages: 1934
Registered: April 2003
Senior Member
Welcome!
The bright channel pre-amp PC203 is designed with an added bright boost circuit that uses a bypass switch for the bright knob. If the switch becomes intermittent and does not make clean contact it will kill the signal through the pre-amp. Try switching it back and forth a few times and see if the sound is restored.

The Boost channel board PC403 has the selective boost and the harmonic clipper circuit. If you hear the noise from the boost switch, then that circuit is probably working. The noise is probably caused by a cap that is switched in the circuit that has a slight charge built up in it. Turning the switch causes the cap to discharge as it is being placed in and out of the circuit.

Have you tried switching on and off the clipper control? The clipper circuit falls between the boost and the pre-amp input stage. If the switch on the control is not clicked off the bypass circuit will not work.

If you have dc on the output, you will need to have the power amp looked at. If you have a voltmeter, see if there is any dc on the output jack (no speaker hooked up). I don't know what you were doing when the spark happened, but you should not have the amp on while connecting the speaker cable.

As for the pilot lamp, it will not cause any problems if it is missing the bulb. Just be sure to replace it with the correct one when you want to.

Buzz in the speakers is rarely caused by bad jacks or wiring. It is possible, but unlikely. Do both speakers sound the same? Is it something loose in the cabinet that could be buzzing?

Hope this helps.
Re: k200b-3 questions [message #11696 is a reply to message #11695] Sat, 29 August 2009 16:57 Go to previous messageGo to next message
jccoombs is currently offline  jccoombs
Messages: 2
Registered: August 2009
Junior Member
Hey thanks for the replies. I played my acoustic 320 throught the cab last night at practice and it sounded great, it is still a little buzzy but its not intrusive and like I said the cab sound loud and full. Other posts here have indicated that some of the altec cabs were 4 ohms. This would make sense since it sounded much louder than it should at 8 ohms. As for the head, I'll check the suggestions and if I have no luck then Ill send it to a tech.
Thanks again
Re: k200b-3 questions [message #11704 is a reply to message #11696] Sun, 30 August 2009 17:31 Go to previous messageGo to next message
BC
Messages: 570
Registered: March 2000
Location: Kentucky
Senior Member
I once bought a 2x15 cabinet with a buzz. Brought it home expectig to change a speaker and found the "Kustom" badge had one loose screw on one side and it vibrated on certain notes, so be sure to check everything! BC Cool
Re: k200b-3 questions [message #27187 is a reply to message #11684] Sun, 03 February 2019 11:35 Go to previous messageGo to next message
terminal is currently offline  terminal
Messages: 20
Registered: June 2009
Location: GEORGIA
Junior Member
I have a K200B-3 and the selective boost switch pops when selecting different positions as well. In the right most position it actually pops repeatedly. It seems to work correctly in all positions (except that last one, the popping is too startling to leave in that position). popping makes we think of a cap, maybe C418 or C419? (only caps in play...) Is popping normal for selective boost ? (can't imagine it would be...)

My PC403 is 100% functional except for the popping on the selective part.

jccoombs, did you sort your K200B-3 out?


I also noticed a couple mistakes in the factory service manual (FSM) for PC403 (on this website). on the layout diagram Q409 and Q410 are flip flopped and on the schematic the top part of the boost frequency selector switch shows a line between C418 and R453. This shorts out whatever resistor is selected by the switch. I studied the traces on the board and this is in fact as error (otherwise, no need for the switch!).

Re: k200b-3 questions [message #27188 is a reply to message #27187] Sun, 03 February 2019 16:41 Go to previous message
chicagobill
Messages: 1934
Registered: April 2003
Senior Member
If you check the later version of the schematic Rev. 3, that line has been removed.
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