|
|
|
|
|
|
| Re: Schematic Accuracy [message #20104 is a reply to message #20097] |
Mon, 10 February 2014 10:26   |
bluezebra
Messages: 89
Registered: February 2014
Location: Lafayette, LA
|
Member |
|
|
|
Actually this is a result of a thumping noise in the tremolo circuit I'm trying to fix. I have already completed all of the recommendations that are mentioned on this forum. It has been recapped, cleaned, treated with Deoxit, new bridge rectifier, replaced every tantalum capacitor, all new transistors, new connections wires, all diodes checked, new three prong cord. The amp works fine (reverb and tremolo) and is now "studio" quiet, but has a thump in the tremolo that is affected only by the speed pot.
|
|
|
|
| Re: Schematic Accuracy [message #20106 is a reply to message #20097] |
Mon, 10 February 2014 12:40 |
chicagobill
Messages: 2006
Registered: April 2003
|
Senior Member |
|
|
Like all manufacturers, all of the production changes at Kustom may or may not have been fully documented. And even if they were, they may not have made it to the general dealership network where most of the available on-line schematics have come from.
I usually don't worry about mismatches unless there is a known common problem that can be fixed by a circuit revision.
Regarding the tremolo thumping, when you turn down the intensity control does it go away? And of course, if you turn it off with the footswitch it stops, correct?
|
|
|
|
|
|
|
|
|
|
| Re: Schematic Accuracy [message #20111 is a reply to message #20097] |
Mon, 10 February 2014 16:24 |
chicagobill
Messages: 2006
Registered: April 2003
|
Senior Member |
|
|
There are a few ways that the trem could cause a constant thump. One is because the intensity control doesn't really turn off the modulating signal and the another way is through the power supply lines.
Try directly grounding the wiper of the intensity pot and see if that helps. If the intensity control is working then try checking the plus and minus 8 volt lines for any signs of interference.
Beyond this, there could be interference from wiring or lead dress.
|
|
|
|
|
|
|
|
| Re: Schematic Accuracy [message #20114 is a reply to message #20097] |
Tue, 11 February 2014 12:22 |
chicagobill
Messages: 2006
Registered: April 2003
|
Senior Member |
|
|
The higher voltages could be caused by modern line voltages, but I'm more surprised to see the big difference between the two 8 volt supplies.
The negative supply tracks the positive one, so you don't normally see that much difference between the two. Maybe that could contribute to the thumping problem.
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
| Re: Schematic Accuracy [message #20121 is a reply to message #20097] |
Thu, 13 February 2014 10:43 |
chicagobill
Messages: 2006
Registered: April 2003
|
Senior Member |
|
|
I don't own a 100 head so I can't help with a photo.
The question regarding the two PNP transistors is simple, while each one is rated for 80 volts they have different current ratings. The bigger one is used as the pass transistor for the regulator while the smaller one is just used to control the bigger one.
The 1N3754 diode is part of the bias string for the two output transistors. The only thing that it will change is the voltages at the bases of the drivers Q127 and Q128.
As for the caps in the regulators, unless there is a major circuit meltdown, they will never see the 40 volts from the main power supply.
|
|
|
|
|
|
| Re: Schematic Accuracy [message #20123 is a reply to message #20097] |
Thu, 13 February 2014 14:40 |
chicagobill
Messages: 2006
Registered: April 2003
|
Senior Member |
|
|
Okay, I didn't understand and I also didn't look at the schematic. The 2N4249 is the generic number, the 38734 is the Kustom part number for the equivalent transistor.
What is it about the main 40 volt supply that you are trying to fix?
Q131 is shown on the transistor layout between Q115 and Q107 just above the speed control R148.
|
|
|
|
|
|
|
|
| Re: Schematic Accuracy [message #20126 is a reply to message #20097] |
Thu, 13 February 2014 16:14 |
chicagobill
Messages: 2006
Registered: April 2003
|
Senior Member |
|
|
|
I have access to two versions of the schematic Rev.3 and Rev.4, the Q131 circuit mod is shown on both and the transistor is drawn in on the location diagram directly under the "sis" in word transistor.
|
|
|
|
|
|
|
|
|
|
|
|
| Re: Schematic Accuracy [message #20135 is a reply to message #20097] |
Fri, 14 February 2014 13:04 |
chicagobill
Messages: 2006
Registered: April 2003
|
Senior Member |
|
|
If your board is early enough, there may not be a Q131. I haven't been able to find any earlier K100-2 schematics than Rev.3.
On the Rev.3 version the entire section that contains Q131 is in bold, which usually means that it has been revised from the original version. So maybe it was added in later to correct some problem.
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
| Re: Schematic Accuracy [message #20168 is a reply to message #20097] |
Mon, 17 February 2014 13:25 |
chicagobill
Messages: 2006
Registered: April 2003
|
Senior Member |
|
|
The 40 volt power supplies will rarely be exactly equal. There are far too many variables that can cause a volt or two difference.
The 8 volt supplies are normally fairly close in value, as the negative supply tracks or follows the positive supply.
As far as R152 is concerned, it is there to limit the amount of signal from the low frequency oscillator going to the tremolo modulator. So it is sort of like a pre-depth control resistor that will limit how deep the effect will go.
If you take a voltage reading at R152, you should find a rising and falling voltage that changes rate with the speed control. If you don't find this voltage, then the oscillator may not be running.
|
|
|
|
|
|
|
|
|
|
VintageKustom.com
Search
Help
Members
Register
Login
Home
]