Cathode bypass capacitors are not absolutely necessary in a circuit. However, their presence or absence in an amplifier affects three things: gain, frequency response, and hum.

If you feel that your amp is lacking in any of these aspects, determining whether the cathodes are bypassed is a good place to start.

The filter capacitors in many amps are mounted in a metal can, which can be an obstacle to successfully recapping the amp. These days, filter cans are only made in a limited values, so it's hard to find the exact match. Mounting the caps outside of the can is another option, but finding the space can be tricky. Removing the can can leave a giant hole, which can allow dust to enter the chassis over time. So, what's the best way to replace can-style filter capacitors?

We have a few Wurlitzer 200 circuit boards that we use for parts. Most of repairing vintage equipment is maintaining a large hoard. Just because a component is obsolete doesn't mean it's useless: a lot of old transistors and diodes are both absolutely necessary and hard to source. We do our best to keep a surplus when possible.