[Amps] Source of 811A or 572B tubes?

[RCM]

> On Dec 29, 2020, at 14:33, Benjamin Deovlet via Amps <amps at contesting.com> wrote:
> 
> I used MFJ 811A tubes in my Collins 30L-1 amplifier.  Apparently they aren't suitable for horizontal mounting.   

I’m not where I can look it up, but there are notes in handbooks about which pins should in a vertical line.

Something about sagging filament or grid.

Guess newer manufacturers messed with the internal structure.