So here I am tinkering around with a pretty much done deal home brew amp.
Today I hooked up a variac to the HV transformer to bring this amp up
slowly.
Now I have questions since I popped a glitch resistor at 1kv. The gu84b tube
uses 330v on the
Screen grid, -130 on the control grid and I had 1kv on the plate. The
cathode is essentially grounded.
When I move the voltage on the control grid to -60 no rf input the control
grid (has a 50ohm resistor
To ground), I get a good show of cathode current, ( I tapped onto the
cathode and a .7ohm resistor to ground.)
Reading the specs for this tube(tons of times) there are various test
methods they use to show
You how it runs, some have 750v on the plate, some have 2kv, I am ASSUMING,
that with the control grid at
-60v and 330v on the screen grid, this tube is going into conduction. I
raised this to -70v and I still get quite
a bit of cathode current, then the glitch resistor popped. I heated this
tube for a good 5 or so hours before
putting it into this testing.(I know some say 12-15hrs) Perhaps its still
gassy and hence the "glitch"? I have a 22ohm 5w which is probably
way small. I wanted it to blow at this low plate volts if any problems
arose. I can put a meter across the 22ohm
and see what the tube is pulling for current. Also I noticed that when going
into "conduction" the plate voltage
dropped a LOT say to 750 or so. Is the variac causing me issues with
current? It's a type 100r genrad
anyway throw some thoughts at me, I'm listening before the next glitch r
goes :-)
chuck
http://www.tomstubes.com/gu84b.htm
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