[Amps] grid fuses

[GGLL]

Joe Subich, W4TV escribió:
> Lon W. Cottingham writes: 
> 
> 
>>but why pay $200 ++  for a 3-500Z when a 6 cent, 1/4 watt resistor, 
>>can/will save them from certain demise from several very common 
>>faults?
> 
> 
> If fusing the grid is so "safe" why is it not used in commercial 
> transmitters?  If it protects a tube so well, why has no tube 
> manufacturer recommended it (they recommend a surge limiting resistor
> in the anode circuit)?  
> 
> I have worked on many commercial and broadcast transmitters over the 
> past 30+ years and not one had any kind of grid fusing.  Every one of 
> them had current limiting in the anode circuit and many had electronic 
> "trips" that would dump the stored charge in the power supply (known 
> as a "crowbar") in the event of a fault.  In fact, a "fuse" in the 
> grid circuit is the opposite of what a qualified design engineer would 
> use as it would keep the transmitter off the air until a maintenance 
> person could physically strip down an amplifier to replace the fuse 
> rather than simply reset/recycle when the fault clears. 
> 

	IMHO, an electronic protection system in a commercial transmitter (I mean for 
TV or broadcast) where it must be on the air continuously is the optimum 
solution. I do not work in that area but I figure they are designed as in RF 
heating machines, where in case of a fault (mostly arcs, a failure of 
intermittent nature)  it trips upto a number of times, recycling power off and 
on. In case of a severe permanent fault, and being completed the recycling 
times scheme, the machine stops working.
	But for an amateur transmitter, you can replace a resistor (yes, a little 
more work involved) and get on the air again. If the fault is severe, both 
systems will keep you busy until the problem is resolved.
	An electronic protection board is welcome, I don't see anybody disqualify 
this option, but it is not so simple and more costly, speaking in terms of 
amateur amplifiers


Best regards
Guillermo - LU8EYW.