There's no way to see if the tube breaks down with HV applied, other than by
putting HV on it. If your only source of HV is your amplifier, then you can
put a light bulb in series with the anode cap, so that the bulb will burn
out and act like a fuse if there's an internal short in the tube. (Be very
careful to observe safety precautions when you do this.) If it passes the
test, then repeat it, this time keying the amp relay so the amp will draw
resting current. Don't connect an exciter to the amplifier with any of these
tests. If you draw normal resting current (typically about 100mA) and the
bulb glows dimly, then there's no short in the tube.
Before you do any of the HV tests, however, you should try keying the amp up
with the plate cap disconnected with the meter switch in the grid current
position. Apply a LITTLE RF drive, not more than about a watt, and see if
the grid current meter kicks up. If it does, then there's no grid short in
the tube. Be careful not to apply too much RF drive if you do this, or
you'll burn out the grid.
73,
Jim W8ZR
> -----Original Message-----
> From: Amps [mailto:amps-bounces@contesting.com] On Behalf Of Drax Felton
> Sent: Friday, April 19, 2013 12:52 PM
> To: Amps@contesting.com
> Subject: [Amps] How to test an 8877 tube
>
> How can I test an 8877 tube for an internal short or other issues other
than
> blowing things up in an amp?
>
> Perhaps cold or with just the heater on?
>
>
>
> A simple continuity test doesn't show any connections from plate, to grid,
> to the pins.
>
>
>
>
>
> Drax KB3X
>
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