Surge Recovery - Burned PC board issue. Techs?

There is a small area arround one of the valve-sockets after surge that was fryed with leads to the cathode feed elements 47uF/100V cap, 1k resistor and 10Ohm bias-resistor.
The cap in fryed area has a voltage 53.4uV drop to 10mA current(I assume it's damaged)
I've also measured cathode feeds for the different bulbs and they seem to be 2% less of the nominated value while the manufactured tolerance is no less than +-0.25%.
My cautions are that even if I replace the damaged elements the fryed PC board area can have an unwanted voltage drop.
Should I somehow cut out this area as whole and wire-up the surrounding elements instead?
848a036e efd3 4d69 a7de 31c247c14aadmarakanetz
What i would do in such a case is measure the resistance of the trace and connections themselves. If they seem to be resistive, it is probably best to bypass them. You can simply use a Dremel type tool with the correct tip or a sharp blade and slice the traces prior to arriving at the damaged area. From there, you can wire from the good side of the trace to the point where the trace terminates at. You should try following the path and length of the trace as closely as possible.

Some would say that you could forget the whole trace and wire point to point, which is another valid approach, but you might also change the impedance of the circuit quite drastically by doing such. The method that i suggested should maintain any pre-calculated impedances within the circuit as closely as possible. Just bare in mind that double sided boards ( if properly designed ) also take into account the capacitance between the top and bottom plating, so try to keep the wire as close to the board as possible. With that in mind, some people will simply solder wire on top of the damaged trace, reinforcing it with solder. All of these are valid approaches with different takes on how to solve a relatively common problem.

Bare in mind that burning or arcing can many times leave carbon residue. Carbon is conductive and can literally bridge circuits, detune impedances and / or even ignite if provided with enough voltage and current. As such, you can try using a chemical electronics type cleaner or very high purity alcohol and an old toothbrush to scrub the board clean. Just make sure that you do your best to drain off any excess liquid AND allow adequate drying time prior to firing the unit back up. In severe cases where arcing has actually burned into the board and there is a large quantity of carbon residue, i have seen circuit boards literally "flame up" due to stray conductivity. The only solution here is to cut out / remove the damaged area of the board and bridge / jump connections as needed. Not a pretty site, but it is better than tossing an otherwise functional device into the garbage. Sean

Sean, Your help is always appreciated!
1.Fortunately the PC-board is not double-sided and I don't have to count on the capacitance between the sides of the PC-board! Tracing the signal path is relatively easy for me as I can open the other monoblock that is OK:)
2.Unfortunately the fry-hole is sufficiently deep(but not large), conductive and inflict the supply voltage to enter the signal flow path. I probably might have to drill it completely out and If it's not the case, what is the best chemical that I need to use to exterminate and clean all the carbon and how I can acquire one? At least I might have to clean the carbon dust arround the rest of functioning elements and the board.
3.What gauge of jump-wires should I use if the DC supply of VTL is 50V on the cathode? The leads on PC-board are 4mm on the signal path and 5...5.5mm on the ground path.
5.The cap's body as well as resistor body is damaged and fryed arround the surge area and I will order them just in case. I know that there could be some tolerance on the caps but I believe that 53uV for 10mA current is large enough drop whad'ya say?
M: 2) You can use VERY high purity alcohol ( at least 91% and preferably 99% ) if you like. The lower the percentage of purity, the more water and contaminants it will contain and the longer it will take to fully dry out. As such, avoid firing the product up until you are certain it is dry.

Other than that, any good "non-lubricating" electronic component cleaner can be used. You can typically find these at MCM Electronics, etc... Just be careful if using a solvent that can eat plastic and damage painted finishes ( and most "good" solvents do ). If you are this far involved in a project, i probably need not mention it to you. I mentioned this primarily for those that might be just starting out. As such, placing an old towel around the area to be sprayed "should" catch the majority of run-off. You may have to spray and scrub or even "chip" the carbon off if severe enough. If it is that severe though, simply using a Dremel type tool with a small "dental" type bit can drastically speed up the process AND reduce the chances of the board flaking or cracking in other nearby areas.

3) I am not good at converting surface area of a conductor to a specific gauge. Hopefully someone will volunteer the info that you need or you'll be able to find some type of conversion chart on the net.

Having said that, i would try to stick with wiring that was very close to the gauge of the OEM trace. That is, if you are trying to maintain the same appr circuit stability and voltage drops, etc... from one monoblock to the other. While you could simply say "heavier is better" so as to minimize series resistance, the amps may actually perform slightly different under heavy loads.

One other caution. Pay close attention to wire routing and the voltage rating of the wires that you are using. When you are playing with tubes, some voltages can be hundreds if not thousands of volts. Using wire rated for well above the specific circuit voltage is important and paying attention to wire spacing is always advised. Once again, i state this for those that may not have a lot of experience in this area.

5) First of all, what happened to #4 ??? : ) I can't say if that is acceptable or not, but it does not sound unreasonable. If i were in your situation, i would measure the other amp ( if you have it handy ) and see how that one checks out. Once again, it is not so much a matter of "working / not working" as it is keeping them running within similar parameters.

Hope this helps. Sean