Greetings to all my audio tube lovers. 300B and 6A3!

Hi! I have just completed assembling an Elekit TU-8550 preamp. Wonderful kit; sounds awesome.
just an item of note . . .

Just finished a Elekit TU-8550 preamp. It works beautifully, but when I turn it off (with the power amp still on) it gives a strong POP through the speakers.
???
Thank you all!

Chuck