hi Les, Jim and all
I agree with Jim's answer.
I am also using 50-ohm 100-watt resistor on HV+ line
to avoid any failure of meters, tubes, diodes etc.
It works fine - it will make a big explosion to a small
peep.
I think you need more burn-in of your tube.
I reccomend more 24 hours without HV.
de Han JE1BMJ
----- Original Message -----
From: "Jim Thomson" <jim.thom@telus.net>
To: <amps@contesting.com>
Sent: Saturday, November 26, 2011 2:45 PM
Subject: [Amps] Arcing 8877
> Date: Wed, 23 Nov 2011 16:21:46 -0500
> From: "Les" <Listwa@comcast.net>
> Subject: [Amps] Arcing 8877
>
> Hi All,
>
> I have a 2nd hand 8877 based 144 Mhz amp, built like a rock. Has worked
> fine for over a year, then bang. I saw a flash and of course the fuse did
> its job. The tube in it was maybe 20 years old.
>
> It took out the shunt( resistor and diode) in the Grid and Meter which I
> replaced. I figure I would replace the tube since I had a newer used
> tube.
> I " burned" it in for about 18 hours with the filament and fan running and
> another 6 hours with the HV on, just for good luck.
>
> I keyed it and slowly brought the power up, worked fine at 5 W and at 10W
> in I measured 230W on the bird meter and it flashed again, fuse again. I
> replaced the fuse and powered it up and again at 10 Watts showing 230W,
> but
> the metering was gone and I looked through the vent screen and saw it
> arcing
> intermittently at the age of the fins, above the Anode strap that goes
> around it.
>
> I am looking for advise. Easy to fix the meter shunts, but is it a problem
> with the tube(s), the anode strap is as tight as it goes.... any guesses.
>
> 73s
> Les
> W2LPL
>
> ### Put some back to back diodes directly between B- of HV supply and
> chassis.
> The 6A10's have a 400A surge rating. Use 2 in parallel to make one assy.
> Make
> 2 x identical assy's. Wire em rvs connected as per above. Then do the
> same again across
> your grid and plate current meter. Put a 50 ohm/50-100 watt wire wound in
> series with your
> b+ lead. Install a Hv fuse just prior to the 50 ohm glitch resistor.
> Now you can't destroy
> anything thing inside the amp. The 50 ohm glitch R will limit the fault
> current, and the
> HV fuse will interrupt the fault current. The safety diodes will
> protect the meters. The safety
> diodes between B- and chassis will not let the B- wander more than +/-
> .7 vdc.
>
> later... Jim VE7RF
>
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