[Amps] Amps Digest, Vol 81, Issue 17

[K3vw at aol.com]

In a message dated 9/9/2009 3:00:34 P.M. Eastern Daylight Time,  
amps-request at contesting.com writes:

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Today's Topics:

1. LK500-ZB (Paul  Decker)
2. Re: LK500-ZB (Roy)
3. Re: LK500-ZB  (TexasRF at aol.com)


----------------------------------------------------------------------

Message:  1
Date: Wed, 9 Sep 2009 18:36:50 +0000 (UTC)
From: Paul Decker  <kg7hf at comcast.net>
Subject: [Amps] LK500-ZB
To:  amps at contesting.com
Message-ID:
<802931850.144221252521410630.JavaMail.root at sz0009a.westchester.pa.mail.comc
ast.net>

Content-Type: text/plain; charset=utf-8



I saw a  thread about LK500 and negative grid current.? Was that ever 
solved?  





My LK500-ZB is acting up.?? OK, I think it is my  fault, the amp was on, 
but in standby and I was in the shack hanging a picture  and dropped the 
hammer ontop of the amp (cover on and all) ?  



No visible damage to the case, but now when the amp is turned  on, but in 
standby, the plate current reads about 200mA and the grid current  is pegged 
negative.? Plate voltage is lower than what it used to be, about  2600 V.?? 
Switching between RX/TX doesn't seem to have any affect, I can hear  the 
relay kick.?? One final observation, in RX, one tube starts to glow  orange, 
while the other stays the normal light yellow color.?  



It seems as if maybe somehow the tube is internally shorted or  
something.?? Ideas, suggestions.. 



thanks, 

Paul (KG7HF)  




------------------------------

Message: 2
Date:  Wed, 9 Sep 2009 13:45:32 -0500
From: "Roy"  <royanjoy at ncn.net>
Subject: Re: [Amps] LK500-ZB
To:  <amps at contesting.com>
Message-ID:  <955C343C1BC147E0ADE8A1FB8A496287 at RoyPC>
Content-Type: text/plain;  format=flowed; charset="iso-8859-1";
reply-type=original

About:


"...No visible damage to the  case, but now when the amp is turned on, but 
in 
standby, the plate current  reads about 200mA and the grid current is 
pegged 
negative. Plate voltage  is lower than what it used to be, about 2600 V. 
Switching between RX/TX  doesn't seem to have any affect, I can hear the 
relay kick. One final  observation, in RX, one tube starts to glow orange, 
while the other stays  the normal light yellow color...(etc.)"


My ZB had that happen  several times when using Eimac tubes AND before I 
installed a good in-rush  protection circuit plus ridded it of parasitics. 
Never has occured since  (with RFP tubes). It's surely a grid - to - fil 
internal  short.

73,   Roy      K6XK





------------------------------

Message:  3
Date: Wed, 9 Sep 2009 14:54:17 EDT
From: TexasRF at aol.com
Subject:  Re: [Amps] LK500-ZB
To: royanjoy at ncn.net,  amps at contesting.com
Message-ID:  <d57.333a4d82.37d953d9 at aol.com>
Content-Type: text/plain;  charset="US-ASCII"

Has anyone tried to blow a grid to cathode short  with a high current pulse 
 
of energy? Such as touching the shorted  pins for an instant with a car 
battery.  At this point seems not much  to loose by trying.

73,
Gerald K5GW




In a message  dated 9/9/2009 1:46:57 P.M. Central Daylight Time,  
royanjoy at ncn.net  writes:

About:


"...No visible damage to the case, but now  when the  amp is turned on, but 
in 
standby, the plate current  reads about 200mA and  the grid current is 
pegged 
negative. Plate  voltage is lower than what it  used to be, about 2600 V. 
Switching  between RX/TX doesn't seem to have any  affect, I can hear the 
relay  kick. One final observation, in RX, one tube  starts to glow orange, 
 
while the other stays the normal light yellow   color...(etc.)"


My ZB had that happen several times when  using  Eimac tubes AND before I 
installed a good in-rush protection  circuit plus  ridded it of parasitics. 
Never has occured since (with  RFP tubes). It's  surely a grid - to - fil 
internal  short.

73,   Roy     K6XK



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End  of Amps Digest, Vol 81, Issue  17
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