[Amps] QRO 2500DX MARK lll 4CX800

[Bob Gibson]

Thanks for all the input..I have not done any checking on the amp other than see if I have plate voltage and screen voltage which I do..at least at the meter..I will check the tube socket for voltage as well as the swamping resistor on the input...The few times that I did run the amp I only used 20 watts in for 3k out..which I think is about right for a three tube 4cx800.. I have been building a box to burn in the new tubes..I'm going to send those down to be checked before I burn those in... 

   73s Bob W5RG
 

    On Sunday, March 31, 2019, 7:07:01 AM CDT, Alek Petkovic <vk6apk at bigpond.com> wrote:  
 
 Same thing happened with a Russian GU84B tetrode in the Emtron DX-2SP, 
at my local radio club.  The resistive cathode to grid connection only 
becomes evident as the valve heats up. Strange.

73, Alek. VK6APK

On 30/03/2019 4:37 AM, Bob Gibson via Amps wrote:
> After sending all three tubes down to be checked at D&C Electronics all three tubes came back bad..the test showed..that once the tube comes up to operating temperature there is a resistive cathode to grid short present possibly indicating a warped grid or screen.. My question is why would all three come back the same..I knew one tube was bad but to have all tubes test the same was a little odd..Anyone have any ideas..Bob W5RG
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