|
Re: newbie with filter cap ? [message #19286 is a reply to message #19284] |
Mon, 02 September 2013 12:06 ![Go to previous message Go to previous message](/FUDforum/theme/vk30/images/up.png) ![Go to next message Go to next message](/FUDforum/theme/vk30/images/down.png) |
chicagobill
Messages: 2005 Registered: April 2003
|
Senior Member |
|
|
Welcome to the place. If you go to the Technical section of this site, you will find schematics for many of the K200B series amps. All of the power supplies are wired exactly the same, so it shouldn't be too hard to find one for your amp.
|
|
|
Re: newbie with filter cap ? [message #19287 is a reply to message #19286] |
Mon, 02 September 2013 13:12 ![Go to previous message Go to previous message](/FUDforum/theme/vk30/images/up.png) ![Go to next message Go to next message](/FUDforum/theme/vk30/images/down.png) |
smackoj
Messages: 67 Registered: September 2013
|
Member |
|
|
thanks CB, I finally found the schem with the 2 big filter caps. took a while but click enuf buttons and shazam, there it was and she's purrin' like a kitten at idle. however, now there is some kind of distorted sound on the guitar notes when any kind of gain used? sounds a lot like a cold solder joint or a bad connection somewhere? more t-shooting in store before she plays like she did in '68.
smacko jack
[Updated on: Mon, 02 September 2013 14:04] Report message to a moderator
|
|
|
Re: newbie with filter cap ? [message #19290 is a reply to message #19284] |
Tue, 03 September 2013 06:38 ![Go to previous message Go to previous message](/FUDforum/theme/vk30/images/up.png) ![Go to next message Go to next message](/FUDforum/theme/vk30/images/down.png) |
stevem
Messages: 4772 Registered: June 2004 Location: NY
|
Senior Member |
|
|
This distrotion you talk about,do you hear it mainly at the end of a note being played and not on the initial attack of the note?
If so, check and see on the under side of the amp chassis that all the 4 output transistors are RCA brand, if one or more is didfferent your distortion could be whats called crossover distortion and this takes place due to mismatched output transistors.
Since you said it looked like someone has done shabby work on the amp, this could be the cause.
It will aslo help out all the filters (electrolytic types) if you leave the amp on over night.
Non use is what condems these filters.
[Updated on: Tue, 03 September 2013 06:39] Report message to a moderator
|
|
|
|
|
|
|
Re: newbie with filter cap ? [message #19322 is a reply to message #19284] |
Thu, 05 September 2013 07:39 ![Go to previous message Go to previous message](/FUDforum/theme/vk30/images/up.png) ![Go to next message Go to next message](/FUDforum/theme/vk30/images/down.png) |
stevem
Messages: 4772 Registered: June 2004 Location: NY
|
Senior Member |
|
|
At this point after checking that the ground off of the round rectifier bridge is good, you need to face the fact that the two main filters are DONE!
Some of these hang in there way longer than 40+ years, but in a amp that did not see much use, or any use this late in its life the filters must go to get the 120 hz hum out.
Mouser electronics sells Sprague brand replacement/up grade part number 3GDY103F100CB2A, It a 10,000 mfd 100 volt filter can.
Mouser also carrys a Mallory brand with the same specs that is a 1 inch taller and works in amps with out reverb, but you may need to extend some of the wires to the filters.
At any rate, get those two orignal filters into the trash!
[Updated on: Thu, 05 September 2013 07:40] Report message to a moderator
|
|
|
|
|
|
|
|
|
Re: newbie with filter cap ? [message #19333 is a reply to message #19284] |
Thu, 05 September 2013 13:14 ![Go to previous message Go to previous message](/FUDforum/theme/vk30/images/up.png) ![Go to next message Go to next message](/FUDforum/theme/vk30/images/down.png) |
chicagobill
Messages: 2005 Registered: April 2003
|
Senior Member |
|
|
All of the Kustom amps have had the ground wiring routed to reduce the ground loop hums. If the wiring to the filter caps has been changed from the original factory wiring, that alone may be the cause of your problem.
The fast test for any Kustom main filter cap, is to parallel a known good cap of equal value and ratings across the original one. If the hum is reduced then the filter cap is suspect, if the hum doesn't change then changing the cap is probably not needed.
|
|
|
Re: newbie with filter cap ? [message #19337 is a reply to message #19333] |
Thu, 05 September 2013 17:58 ![Go to previous message Go to previous message](/FUDforum/theme/vk30/images/up.png) ![Go to next message Go to next message](/FUDforum/theme/vk30/images/down.png) |
smackoj
Messages: 67 Registered: September 2013
|
Member |
|
|
I appreciate the help. and yes, the wiring was moved by a previous owner, tech or backyard mechanic. I don't have a reference source for how they came from the factory though. The amp is a 1968 K200B-4.
I have a new set of filter caps I can jump across these old Mallories and I'll give an update asap.
ps. to Steve; the 'round rectifier' is gone and a newer square one is in place. that seems to be the reason that someone moved wires around before but other things could have happened and I wouldn't know it?
[Updated on: Thu, 05 September 2013 18:43] Report message to a moderator
|
|
|
|
Re: newbie with filter cap ? [message #19344 is a reply to message #19284] |
Fri, 06 September 2013 02:45 ![Go to previous message Go to previous message](/FUDforum/theme/vk30/images/up.png) ![Go to next message Go to next message](/FUDforum/theme/vk30/images/down.png) |
chicagobill
Messages: 2005 Registered: April 2003
|
Senior Member |
|
|
Please describe your wiring from the power transformer secondary to the rectifier and from the rectifier to the filter caps. As I remember it the important grounds are the center tap of the secondary and the speaker output ground wires.
This weekend I will pull out one of my K200B chassis' and detail the original wiring for you. Maybe it will help.
|
|
|
|
|
|
Re: newbie with filter cap ? [message #19351 is a reply to message #19284] |
Fri, 06 September 2013 13:55 ![Go to previous message Go to previous message](/FUDforum/theme/vk30/images/up.png) ![Go to next message Go to next message](/FUDforum/theme/vk30/images/down.png) |
chicagobill
Messages: 2005 Registered: April 2003
|
Senior Member |
|
|
Original transformers were pop riveted into the chassis. This doesn't mean that your transformer hasn't been replaced.
Off the top of my head, it sounds like too many grounding points. I won't know for sure until I pull out a chassis, but I think that the CT of the secondary has to go directly to the filter caps. Same with the ground wire from the output jacks. The entire power supply grounds to the chassis at the output jacks.
Check the date code on the transformer and compare it with the date codes on the pots. That may give you some insight as to the originality of the transformer.
Steve's suggestion of checking for dc on the output is a good one.
|
|
|
|
|
Re: newbie with filter cap ? [message #19359 is a reply to message #19284] |
Sat, 07 September 2013 02:29 ![Go to previous message Go to previous message](/FUDforum/theme/vk30/images/up.png) ![Go to next message Go to next message](/FUDforum/theme/vk30/images/down.png) |
chicagobill
Messages: 2005 Registered: April 2003
|
Senior Member |
|
|
Pleat, you may be right but we need to know what two wires have been cut and spliced.
What are the pot codes and the transformer code? As for the serial number, search the board here and find the serial number date list that Les Strickland posted. The list will give you an approximate date that the amp was produced.
I checked my K200B-1 and this is how the power supply secondary is wired. The two purple secondary wires connect directly to the AC inputs of the bridge rectifier.
The positive out from the bridge goes to the positive terminal of one filter cap. The negative out goes to the negative terminal of the second filter cap.
The gray secondary center tap wire goes to the negative terminal of the positive side filter cap. There is a black wire from the same negative terminal that grounds to the chassis at the speaker output jack. Finally there is a short black wire from that same negative terminal that connects to the positive terminal of the negative side filter cap.
So the entire power supply single point grounds to the positive filter cap's negative terminal and that terminal point grounds to the chassis at the speaker output jack.
A technical point here, the green ground wire from the ac cord should be (by code) connected directly to the chassis to its own screw terminal. Not a common point or to a mounting screw for something else. The green wire should also be longer than either the hot or neutral wires (black and white), so if the cord should be pulled out of the amp, the green wire will stay connected to the chassis after either the black or white wire has been pulled loose.
|
|
|
|
Re: newbie with filter cap ? [message #19366 is a reply to message #19364] |
Sat, 07 September 2013 09:24 ![Go to previous message Go to previous message](/FUDforum/theme/vk30/images/up.png) ![Go to next message Go to next message](/FUDforum/theme/vk30/images/down.png) |
smackoj
Messages: 67 Registered: September 2013
|
Member |
|
|
ok; changes made to wiring to copy factory, NO chg in hum. I am now looking at two possibles;
1. the pwr switch is bad?
2. having the reverb pan disconnected creates a hum?
I took the reverb pan off first thing and have done all my tests without it hooked to the amp.
thanks, smacko
ps. OOPs 3 poss.
3. the pilot light does not have a bulb in it? waiting for the 28 volt ones to get here via mail.
[Updated on: Sat, 07 September 2013 09:27] Report message to a moderator
|
|
|
Re: newbie with filter cap ? [message #19367 is a reply to message #19366] |
Sat, 07 September 2013 10:21 ![Go to previous message Go to previous message](/FUDforum/theme/vk30/images/up.png) ![Go to next message Go to next message](/FUDforum/theme/vk30/images/down.png) |
smackoj
Messages: 67 Registered: September 2013
|
Member |
|
|
further tests: with no input signal and spkr connected, humming gets much louder by raising vol on the right side channel aka pc403. adding vol. to other channel, pc303 does not add any hum.
power tran code 1005836
pot code 304813
ser. num. 27851
gracias amigos
[Updated on: Sat, 07 September 2013 10:27] Report message to a moderator
|
|
|
|
|
Re: newbie with filter cap ? [message #19370 is a reply to message #19284] |
Sat, 07 September 2013 12:25 ![Go to previous message Go to previous message](/FUDforum/theme/vk30/images/up.png) ![Go to next message Go to next message](/FUDforum/theme/vk30/images/down.png) |
chicagobill
Messages: 2005 Registered: April 2003
|
Senior Member |
|
|
Pleat is right, the switch can not cause your hum.
Now you tell us that the hum is changed by the controls on the right channel. If that's the case, then there may be a problem with the grounding connection or with the board itself. Maybe a bad cap or transistor. The quick test is to unhook the blue output wire that connects the board to the power amp board. If the hum goes away then you have found your problem.
If you turn down the reverb control or turn off the reverb with the foot switch there should not be any hum from the reverb circuit.
Not having the pilot lamp installed will not cause any hum.
The pot code and transformer code dates the amp to a probable 1968 construction.
The preamp boards make their ground connection through the input jack wiring. The power supply grounds through the speaker jacks, and the power amp grounds with a small wire that gets screwed down by one of the pc board mounting screws. If any of these connections get loose, dirty, oxidized, etc. there can be problems with the amp.
|
|
|
|
Re: newbie with filter cap ? [message #19373 is a reply to message #19371] |
Sat, 07 September 2013 13:47 ![Go to previous message Go to previous message](/FUDforum/theme/vk30/images/up.png) ![Go to next message Go to next message](/FUDforum/theme/vk30/images/down.png) |
smackoj
Messages: 67 Registered: September 2013
|
Member |
|
|
all inputs pulled off chassis and checked/filed shorting pin with no imprv. the blue feed wire from the pwr amp disconnected. at last, 50% imprv. but still a lot of hum. I think I need to re-visit the pwr filter caps? I continue my quest to slay the monster....wish me luck.
jack
[Updated on: Sat, 07 September 2013 14:36] Report message to a moderator
|
|
|
Re: newbie with filter cap ? [message #19374 is a reply to message #19373] |
Sat, 07 September 2013 19:00 ![Go to previous message Go to previous message](/FUDforum/theme/vk30/images/up.png) ![Go to next message Go to next message](/FUDforum/theme/vk30/images/down.png) |
smackoj
Messages: 67 Registered: September 2013
|
Member |
|
|
Stardate Log; 2296.5; the K200 is alive 60% less hum. I believe the remaining hum is a combination of power filter dry rot and poor grounding along the front panel (14 pots and switches)maybe still an issue with the four input jacks also? thanks to all my new friends for your eager input.
jacko
[Updated on: Sat, 07 September 2013 23:31] Report message to a moderator
|
|
|
|
|
Re: newbie with filter cap ? [message #19377 is a reply to message #19284] |
Sun, 08 September 2013 14:46 ![Go to previous message Go to previous message](/FUDforum/theme/vk30/images/up.png) ![Go to next message Go to next message](/FUDforum/theme/vk30/images/down.png) |
chicagobill
Messages: 2005 Registered: April 2003
|
Senior Member |
|
|
Well, I'm glad that you got it working to your satisfaction. I would like to know what your reasoning for adding the resistor to what I assume is the 120 volt ac primary is?
I personally would not add that resistor. You are treating the symptom, not curing the disease.
|
|
|
|