Disadvantages of PCB Constructed Amps
I am not going to jump into untying the Gorgon's knot of the PCB vs. hand wired debate about PCBs sucking out tone. There's enough damning evidence without making that case. Here's a few major reasons hand wired still rules for tube amps.
1. PCB's are hard to repair:
A tube amp is meant to be repaired--it not a disposable piece of equipment. If you want an amp that will last a while get one that is hand-wired. Keith Richards has been using a Tweed Twin #006 (sixth off the line) since the late 80's. You don't see any PCB amps in service that long.
It should noted that PCB board amps don't necessary have to hard to work on. Ampeg use to make amps with a removable plates so you could easily access the components and had heavy duty boards. The vast majority of PCB amps are not like this. PCB construction is usually done save labor and cost so manufacturers rarely use high quality boards or consider the serviceability of the amp.
2. PCB's are difficult to mod.
If you get an amp you may want to make some changes to it. You can forget being able to do a proper job on a PCB amp. Maybe you can change a few parts but any groundbreaking mod--nope. You really cripple those possibilities with a PBC board amp. Of course if you like the amp out of the box it's not a problem.
3. PCB's are often poorly laid out.
Many PCB are designed by engineers that are not really musicians or tube fanatics. The PCBs in in may amps made to be as small as possible (so it costs less) but this can cause instability in the amp and places the components in close proximity which cause parasitic effects. For example a customer brought in a Re-issue Marshall 1987X that had a high pitched oscillation. It was caused by the PCB board's layout. Rather than fix the layout problems many manufacturers add bleed off caps that help the amp remain stable by dumping signal and making the amp sound dead.
4. PCB's are damaged by heat.
Tubes produce heat so PCB's eventually fail because of heat unless this issues is deal with. This problem is especially prevalent in amps where the power tubes are directly mounted on the PCB. Again since it is cheaper not to have good heat management so many companies fail to adequately protect the PCBs from heat.
5. PCB's can be damaged by vibration in combos.
While all combo amps make have problems caused by vibrations PCB boards are especially susceptible. The mounted components shake and eventually break the solder joints. Many of PCB board amps I repair have this type of damage. This can happen in hand wired amps but because there is more solder on the connections it doe not happen as often. If it does it's easier to repair.
What is good about a PCB:
1. The labor cost is less thus the price is lower.
This is good thing but the other disadvantages outweigh it unless you view you am as disposable.
PCB board amps are really consistent since most of the construction is exactly the same.
Hand wiring is ONLY superior if it is done correctly. Poor layouts and direct copying of old amps happen a lot in this business and this often makes hand wired amps noisier. At Carl's Custom Amps we do it right. Decades of hindsight allow us to make quieter, more reliable, and safer amps that still sound like they should.