[Amps] Chinese Caps Defective @ RF

[Jim W7RY]

Well I had another Chinese cap blow up on me in my 8877 amplifier. I had 3ea 
1000PF 12KV caps in parallel for the plate blocking caps. I was tuning the 
amp on 10 meters and KERBLEWEY!

I have successfully used 2ea 1000PF 12KV in parallel plate blocking caps 
(just like Alpha does) in my 3CX800 amplifier and they lasted years in RTTY 
contesting. I replaced them a couple of years ago with doorknobs.

One of them shorted (just for a minute ). That blew up the 100K resistor 
that I had across the output of the tank for keeping the voltage from the 
antenna. No big deal.. BUT was the big deal, is the Jennings RJ1A relay 
welded the common to the NO contacts. I was transmitting into a dummy load. 
It also blew the ceramic off of the 25 ohm 25 watt surge resistor that is on 
the WD7S power supply board. The resistor survived but I replaced it anyway.
No other damage other than that.

The effected caps are shown here:

http://www.ebay.com/itm/10-15KV-1000PF-High-Voltage-Ceramic-Disc-Capacitor-Y5T-/150781333576?pt=LH_DefaultDomain_0&hash=item231b449048

I don't think this is the vendor where I bought my caps but they are the 
same blue caps.

I also had a .01 6KV Chinese cap blow up at the base of a TL-922 plate 
choke. Replaced with a Vishay/Sprague/Cerra-Mite .01 6KV and all is well 
(Mouser P/N 75-564R60GAS10 ). But at almost $6.00 a copy, I was trying to 
save a few bucks... How did that work out?

I'm still using the Chinese caps in the 8877 amp to buy-pass the HV in the 
power supply and on the back of the RF deck where the high voltage connects 
(little to no RF here). But I'm using a Visay/Sprague/Cerra-Mite .01 6KV cap 
at the base of the plate choke.

Bottom line... Be careful when using these caps in a high RF environment.
73
Jim W7RY