[Amps] 2nd grid resistor blow Ameritron AMP 811H

D Pipes dpipes at earthlink.net
Mon Aug 15 10:46:32 EDT 2005


late last year I purchased a Ameritron 811-H amp. First amp I have had in years. Back in January i posted on this list my problem that I had blown a grid resistor on the back right side tube. With the help of this list i learn much and replaced the resistor after i also found what I had assumed to be the total reason for the blown resistor. The tube in that socket had a visible defect where the top spring like wires actually had blown loose and cold be shook up and down with light shaking. Anyway replaced the tube with a set of Taylor select (4 matched) from RF Parts. That was in January and all has been perfect.. not an arc not a pop and tuned fine. I kept the 3 "good" tubes and tossed the obvious bad tube.

Well now to the point of this email. Last week I came in to do a little ham radio.. switched on the radio and then as always switched on the amp. POW! arc and glow. Same resistor same tube. I pulled cover replaced the resistor and replaced the tube with one of the original "good" tubes I had. Amp is back to working perfect.

Any ideas? The last fix lasted 7 months.. all perfect. Both times the problem occurred at switch on. opr mode in standby no RF load just when the switch power was turned on. I did re-check the tube that appeared bad (no physical defects seen) and proved that the tube has an internal short. (blew the replaced resistor) .. anyway re-replaced the resistor and put the older "good" tube back in and all is just fine... right now...

Question is.. does this sound  like a tube problem an amp problem or both??

I do have a 3rd party soft start nit that my amp is plugged into and the amp is wired for 240 v

Any suggestions? 
Thanks for nay and all help... 


D Pipes
dpipes at earthlink.net


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