I found this blog on the RS web page and scanned through it. It looks like an interesting read with a few tips.
https://www.rs-online.com/designspark/building-a-valve-amplifier-part-1-design-components-and-layout
https://www.rs-online.com/designspark/building-a-valve-amplifier-part-2-single-channel-prototype-and-loudspeakers-assembly
https://www.rs-online.com/designspark/building-a-valve-amplifier-part-3-testing-the-prototype-adjusting-the-design-and-planning-the-enclosure
https://www.rs-online.com/designspark/building-a-valve-amplifier-part-1-design-components-and-layout
https://www.rs-online.com/designspark/building-a-valve-amplifier-part-2-single-channel-prototype-and-loudspeakers-assembly
https://www.rs-online.com/designspark/building-a-valve-amplifier-part-3-testing-the-prototype-adjusting-the-design-and-planning-the-enclosure
