[AMPS] tuning up a tetrode amp

[Michael S. Mitchell, W6RW]

Hi Lane....I own a homebrew 4CX1500B amplifier......the most important thing to
watch in the tune up procedure is the screen current......the screen in a
4CX1500B only has 12 watts of dissipation available....
I generally adjust the tune control for a dip in the plate current and the load
control for a dip in the screen current.....I dip the plate first without a lot
of drive and then as I start to add drive, I adjust the load control for minimum
screen current. After that, I tweek the two controls for maximum power out while
watching the screen current to keep it as low as possible. Just remember with
350 volts of screen bias, it only takes a little over 34 milliamps of screen
current to be over 12 watts of the maximum scrren dissipation available. I try
to keep the scrren current under 5 miiliamps when I am operating the amp. The
grid of a 4CX1500B has zero watts of grid dissipation available.....so I don't
watch the grid current because if I ever saw any at all the grid would probably
be toasted anyway. The 4CX1500B sings right along with 3KV on the plates drawing
an amp of plate current.....Nice Tube!!

I hope this helps...73 es cul de Mike/W6RW

Lane Zeitler wrote:

> I am almost embarassed to ask this. However, since my ego is inversely
> proportional to my waistline.........I have recently acquired a superb HB
> amp covering 160 to 10. Uses Dahl components in the PS, vac. variables in RF
> deck. built professionally by a EE (now SK, RIP). The tube is a single
> 4cx1500. My questions is how the heck do you tune this up? I have used
> triodes all of my life sans my TS-820/830 which use beam power pentodes in
> the final (2X 6146) but I just tune for max power on these. I have always
> avoided tetrodes mosly due to my ignorance of the tune up procedure.
>
> The amp has metering for screen I and E and also grid I and E as well as
> plate I and E. What is the value I need to watch? I assume that it is not
> safe to tune it like my 3-500zs which is usually just tuning for max power
> out with a string of dits at 60 wpm?
>
> Also, what is the going rate for a good 4cx1500 pull? I figure they are not
> too bad since the military used/uses them and they have been around longer
> than I have been alive.
>
> Lane
> Ku7i
> San Diego
>
> PS I am anxious to see how well my "new" Johnson Ranger will drive this!!!
>
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