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Wiring and PCBs
Hi Guys

I just posted the text below in a different thread but thought it should be here for more general viewing.

In the modern age of computerised PCB layout and overall design, it is very easy to eliminate all the wiring or very nearly so, but this means the whole amp or product is on one board. The chassis must have one panel that can be removed if one is to install or remove the card. It all looks good on the monitor and the assembly is quick, plus the board is complete so it can be tested prior to mounting in the chassis. Even though I am aware of the trap and know better, I have done this myself.

Wiring is the repair person's salvation provided it is done carefully.PCBs on the front panel, PCBs on the rear panel, maybe other PCBs for the PSU etc, wired to each other with generous lead lengths - service loops as they are historically known - allow smaller portions of circuitry to be dealt with more easily. It may end up that to replace a panel pot, say, one has to free all the front panel pots, but if this means you do not also have to free up the rear panel items or other things, then it is one step closer to being a breeze to service. Breaking the control and jack boards into yet smaller pieces makes it quicker still.

The other thing having some wiring does for you is to improve the reliability with regard to mechanical strain due to flexure of the chassis. Typically the pots, jacks and switches secure the PCB to the panel and there can be strain on the solder connections depending on how much overall support there is for the card. A further benefit to having some wiring and smaller PCBs is that each is mechanically only related to a small part of the chassis and therefore measurement and placement is less critical and tolerances of the chassis bends and dimensions is less critical. The reality is that everything is designed at once in the same software, so mechanical alignment will be as good as the chassis fabrication allows.

In the case of the PA66, the PCB is supported by metal standoffs, four around each power tube and three on the front-end. The tube socket leads are bent over for mechanical integrity prior to soldering. The preamp PCBs are similar with enough mounting positions over the length of the board. This is actually quite robust provided one takes the normal amount of care during tube insertion and extraction.

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