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Radio Record, Volume V, Issue 4, 7 August 1931, Page 32

[T* you get an unpleasant "pong" every time you touch your detector valve you can often overcome this by fixing a little plasticine or chewing gum on the top of the valve and embedding a small piece of lead in this to change the natural vibration period of the valve. TE you are building a portable set remember that the modern antimicrophonic valve holder allows of considerable movement of the valves, and that to protect these sponge rubber, or some similar shock-absorbing material, will be necessary.