pentalab wrote:
<snip>
### Not quite. The GRID RING is bonded to the chassis !! This
is not a case like Rich using 1/2 watt resistor's as "grid fuses" [
which WILL leave the grid floating]
agreed
### same deal on a YC-156 and also a socketed 3000/6000.
yeah... and how sweet it is!
### I use several 6 A diodes between chassis and B-... [and also across all the meter's] . When the grid fuse blows the cathode can't float more than +/- .7 V.
That's good and also the 1K safety resistor makes it all good ;)
Also have a 3 A cathode fuse [also a 3agc] in the center tap of
the fil xfmr circuit [ along with the 60 x 6A10 6-A , rotary
switched bias diodes. ] This 3 A cathode fuse has a 1k- 25
watt ressitor across it.
TONY SEZ a little low, use something like 15K to 20K across the
fuse. When the fuse blows you will have an increase in bias that will cut the tube off and will develop a voltage proportional to that needed to cut it off.
### partially agreed. Trbl is... you can STILL drive it.. and get
say 40% output [Class C] I tried a 10-100k across the grid fuse as well. IF the grid fuse blows.... the bias developed will do exactly the same thing as if the cathode fuse blows. [cathode fuse with 1k to 100 kw across it] u still get 40% output.
And that still takes us to electronic protection...
### You can remove the resistor across the grid fuse with NO problem at all. Works better too. With no path for dc grid current... u get zero watts out. Still don't know where the 800+
watts of drive has gone ??
Question is... what's an easy way to obtain a visual indication /led/neon/etc.... to let us know said fuses are blown
???
TONY SEZ if the cutoff bias is high enough, a neon bulb with a
series resistor could be used as an indicator.
### I'm gonna measure the cutoff bias on the existing 100 k 2 w mf
in the vac t/r set up.... on RX. and measure it.
continued below...
I enjoy reading your posts Jim!
## tnx. I didn't know whether to take my marbles home or not.LOL
Best thing I have seen is to use one of the triode control boards and
use the protection circuitry they provide. You will find there's hardly
any failure that will can not be detected and reacted to almost instantly. You might have to make a few adaptations to meet the need for
QRO++ but the principle is the same. This is especially good because it
can trip the amp off line so you don't have high drive going into a
malfunctioning amp.
### I have looked at both triode boards in the past. Some of it would need extensive mods, etc.
But the price is nominal for them... use the pieces you need. Take a little time looking at Paul Hewitt's board (WD7S). He has done some nice work and all his trimmers are multi turn pots.
As far as a grid over
current device goes... the ones depicted in the handbooks work very
well... albeit they all add varying bias.... cuz of the grid current flowing through a resistor [ vdrop used to trigger the 2n222
etc... then a 4pdt latching relay.... hotswitching amp offline,
latching to itself... turning on a led etc. ] I have seen and built
Orr's plate over current device same deal. [ just don't use the
vac relay.. used to open off the HV ]
### During a "glitch".... it's a whole nuther ball game. They all use series diodes... such that during normal operation... slightly excess grid/plate current will simply kick amp offline. During a
glitch.... with huge currents flowing... the safety diodes on the plate/grid protection devices will turn on..limiting voltage to a
safe value.. so the grid/plate overcurrent protection device doesn't
get fried.
## IF plate grid current are slightly over XXX.... the fast fuses
take a long time to blow. During a glitch.... the fuse blow REAL
fast.. and protect the tubes grid, etc. The eletronic stuff...
while fast... still has to activate a mech relay. U can get small
mech relays that will op in <2 msecs however.
### I'm going to try and incorporate BOTH fast fuses and electronic grid/plate current protection... I'll let u know.
I think you're thinking in the right direction. Paul uses solid state relays in primary leads but I'd think they would be difficult to find and very expensive for really big stuff. Of course they can open the circuit quicker than anything else. Only problem is, with that huge capacitor bank, speed on the primary might not be the saving grace.
### also a 2nd high reflected power kick out device b4 the big amp would help.... help to kick the IPA + xcvr off line... IF the
grid fuse in the big amp blew.
Paul does do some neat sensing and comparing input and output. worth looking at!
Love reading your technical details!
73, Tony W4ZT
