[Amps] grid fuses

[Joe Subich, W4TV]

> > If fusing the grid is so "safe" why is it not used in commercial
> > transmitters?
> 
> If seatbelts are so safe, why weren't they installed in our 
> 1940 Chevy?

Non-sequitur, grid fusing was not installed even in the newest tube 
transmitters.  In fact, the grids were generally bolted directly to the 
chassis wherever possible.  If they can't be bolted to the chassis, 
they are grounded through far less than 200 Ohms Xc. 

> > If it protects a tube so well, why has no tube manufacturer 
> > recommended it (they recommend a surge limiting resistor
> > in the anode circuit)?
> 
> Tube mfgs finally approved the glitch R in the + lead of HV-PS --  
> years after some Amateur Radio amplifier builders figured out that 
> it was a good idea.

And a long time after commercial amplifier (broadcast, ISM, etc.) 
designers were using them.  Tube manufacturers have always been 
slow to update their data in view of field experience.  However, 
grid fusing has the potential to cause more problems than it solves 
particularly when other options are available to protect the grid 
in the event of a fault. 

> As I see it, HF transmitting amplifier engineers are/were reluctant  
> to admit that VHF and UHFparasitics are not an impossibility, even  
> though it was pretty obvious that they were rather blissfully  
> ignoring the feedback-C spec from tube mfgs.

Every commercial transmitter I have seen has taken more than adequate 
steps to prevent parasitic operation.  None of that has included 
floating any grid under any circumstance. 

> That's one of my favorites, Joe, but I recently found out that the  
> statement came from a competitor of P. T. Barnum.
> http://www.historybuff.com/library/refbarnum.html

Exactly why I said "is credited with saying" ... nobody knows about 
Hannum. 

73, 

   ... Joe, W4TV