[Amps] Plate choke explodes

[Han Higasa]

Generally small plate RFC can burn with de-tune of the plate circuit
Or

1. two different chokes had similar holes on 50 MHz.
2. the tube oscillates with significant power.
3. the tube has troubles such as grid-cathode touch or
4. arc in the tube - insufficient aging or defect tube.

General setting up/hints are:

Clean up metal tips, dust or powder after any metal works.
Check for proper layout.
Use proper stopping and bypass capacitors around plate circuit.
Bypass cap of the plate RFC, plate output circuits and the input
circuits should share common, short and wide ground for stable
operation.
Always use a 50- or 30-ohm 10W protection resistor in series
of HV+  and cold-end of plate RFC to avoid any HV rush.
Check bias zener diode and bias resistors.
Take aging time (heather and cooling only) for 24 hours.
Use a proper dummy load and a connection cable.
Use lower HV, let it TX state and observe how IP rise.
Drive with 1-3 Watts and check IP and the output rise.
Tune input and output circuits.
Any arc, smoke, noise, fire or IP rush in case, stop immediately.
Rise HV/driving power and tune again...

GL, de Han JE1BMJ

----- Original Message ----- 
From: "Drax Felton" <draxfelton at me.com>
To: <amps at contesting.com>
Sent: Friday, April 12, 2013 9:26 PM
Subject: [Amps] Plate choke explodes


> So I've tried two different plate choke designs on my 6 meter 8877 amp I'm 
> trying to build.   Both times the plate chokes have violently exploded as 
> soon  as I apply 5 watt or less RF input to the amp.
>
> Any ideas what I did wrong?
>
> Sent from my iPhone
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