[Amps] TL-922A - Loud Pop, Blown Fuses

Sun Dec 5 20:17:04 EST 2004

I think the filaments are in series in the 922, so you cannot pull one 
tube and test the amp that way. 
73, Rob, NC0B

Tom Cathey wrote:

>Hi Clay,
>
>That's good - you've made some progress and eliminated 1/2 of the rig.
>
>I take it you have no good 3-500Z spares to try. If not, I wouldn't worry
>about blowing anything up by popping fuses.  Pull one tube out and fire it
>up. If the amp works, try to load it up on 2100V to see if the amp puts out
>some RF. If it does, then switch to the other single tube and see if it pops
>the fuse. It's a 50-50 guess if it's only one tube.
>
>It could be other things too, but this is the shortest path to get right to
>the heart of the problem.
>
>BTW, do the fil pins have ample air going by them? Your overheated fil choke
>might be a clue that there's no air flow below the chassis. I have two
>3-500Z amplifiers here. One has chimneys and is FB. The other had just a fan
>and no air below. It was melting solder out of the fil pins. I ended up
>adding a blower below to correct this and all is FB.  ie, Hopefully you
>didn't damage a tube's seals and loose the vacuum, etc. I assume that they
>both still light up OK?
>
>Check the tubes as above and post again.
>
>73,
>Tom, K1JJ
>
>
>  
>
>>Thanks for the responses.  I didn't think about an internal tube short as
>>    
>>
>a
>  
>
>>possibility.  I removed the plate caps from the 3-500's and the HV
>>    
>>
>measures
>  
>
>>normal (2100V CW, 3100V SSB). Is it logical to assume that one (or
>>    
>>
>possibly
>  
>
>>both) of the 3-500's has developed an internal problem or should I be
>>looking for other causes as well, such as a bias supply problem.  I don't
>>have access to a hy-pot tester, but a simple resistance check from
>>    
>>
>filament
>  
>
>>to grid on both tubes doesn't reveal a short.
>>
>>One thing I didn't mention earlier (because I don't believe it's relevant)
>>is that the small filament choke (L20) that connects to the filament
>>transformer center tap, has overheated in the past.  Since one of the tube
>>filaments came unsoldered from the pin (a simple soldering job fixed it),
>>    
>>
>I
>  
>
>>figure all of the extra current flowing through the small choke was the
>>cause of that.  Other than some discoloration, it appears ok.
>>
>>Any and all suggestions are welcome.  I don't want to risk my power supply
>>by blowing more fuses trying to determine which of the tubes might be at
>>fault.
>>
>>73,
>>Clay  W7CE
>>
>>
>>----- Original Message ----- 
>>From: "K7RDX" <k7rdx at earthlink.net>
>>To: "Clay Curtiss W7CE" <w7ce at curtiss.net>
>>Sent: Saturday, December 04, 2004 5:42 PM
>>Subject: Re: [Amps] TL-922A - Loud Pop, Blown Fuses
>>
>>
>>    
>>
>>>Hi Clay, pull the tubes and start the amp again. If plate voltage is
>>>      
>>>
>>normal
>>    
>>
>>>and the fuse doesn`t blow again, shut everything down and inspect the
>>>      
>>>
>tube
>  
>
>>>sockets for burnt or damaged rf chokes from the three grid pins to
>>>      
>>>
>ground.
>  
>
>>>If one of the tubes flashed over, some of  these chokes will probably be
>>>destroyed or at least damaged. 3-500z tubes sometimes develop a short
>>>      
>>>
>from
>  
>
>>>grid to filament after a period of use and will flash over on the next
>>>start-up. If you have access to a hypot tester, a shorted tube is easy
>>>      
>>>
>to
>  
>
>>>spot...Hope this helps you find the problem...A flashover might damage
>>>      
>>>
>the
>  
>
>>>bias as well as the high voltage supply. 73,Jim.
>>>----- Original Message -----
>>>From: "Clay Curtiss W7CE" <w7ce at curtiss.net>
>>>To: <amps at contesting.com>
>>>Sent: Saturday, December 04, 2004 12:05 PM
>>>Subject: [Amps] TL-922A - Loud Pop, Blown Fuses
>>>
>>>
>>>      
>>>
>>>>Yesterday morning when I turned on my TL-922A, there was a very loud
>>>>        
>>>>
>pop
>  
>
>>>>followed by blown fuses.  I replaced the fuses, changed the setting to
>>>>        
>>>>
>>CW
>>    
>>
>>>to
>>>      
>>>
>>>>reduce the B+ voltage and tried again.  Similar result with several
>>>>        
>>>>
>>>smaller
>>>      
>>>
>>>>pops and then blown fuses.  I use a footswitch for T/R control and it
>>>>        
>>>>
>>>wasn't
>>>      
>>>
>>>>depressed nor was I transmitting with the exciter when I powered up.
>>>>        
>>>>
>I
>  
>
>>>>should also mention that I've heard a pop on power up two times
>>>>        
>>>>
>>>previously,
>>>      
>>>
>>>>but neither time caused a blown fuse.  I opened it up today for a
>>>>        
>>>>
>visual
>  
>
>>>>inspection and see no signs of arcing or anything unusual.
>>>>
>>>>Before I dig into this thing, has anyone else experienced this
>>>>        
>>>>
>problem?
>  
>
>>>Any
>>>      
>>>
>>>>hints or suggestions to reduce the troubleshooting time will be
>>>>        
>>>>
>>>appreciated.
>>>      
>>>
>>>>Thanks and 73,
>>>>Clay  W7CE
>>>>
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>>>>http://lists.contesting.com/mailman/listinfo/amps
>>>>        
>>>>
>>>      
>>>
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>>    
>>
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