On 2012 Jan 31, at 7:14 PM, Ian King wrote:
 I have a 561A that makes me happy.  :-)  I do need to clean its
 switches,
 though.  FWIW, I'd love to find a 3A74 plug-in for it.  There's enough
 stuff that I do with vintage machines, requiring not screaming hot
 bandwidth but multiple inputs, that the 3A74 would just be far too
 cool
 for words.  Just sayin' 
There is a 4-channel plug-in (presumably a 3A74) in one of the 500
series Tek scopes at the radio museum here. Not sure which 5xx base
it is in. I'd love to be working on it.
I have this nagging fear one day I will go in to the museum and
somebody will have thrown out the tek scopes. 
Have you ever heard the phrase "justifiable homicide"?  OK, kidding -
mostly.  - Ian