Need help with a Crack modification

[InnerTube]

I bought this amp from a member, however, I have not received a reply from him regarding this component. This piece fell off the amp and I am having trouble knowing what it is and how to replace it. I am attaching photo of the component as it was attached to the amp and also a couple of photos of the component alone. The amp still plays so I am wondering if this is an essential part, it it should be reattached or replaced with a new one.

Thanks in advance for very much appreciated help, JS

 

[Paul Birkeland]

That is a critical part.  While the amp may pass signal as it is now, the B+ voltage will be pretty low without that part installed.