[AMPS] 8873 replacement

[Rich Measures]

>
>
>On Mon, 12 Oct 1998 11:12:10 +0100 "Doug Klein, K4LT" <k4lt@fuse.net>
>writes:
......
>>Ok, hello out there to all the technical guru's!  This is Doug, K4LT 
>>and I am NOT much of a technical wiz.  Can anybody help me?
>>
>>I have my Henry 2k Ultra on the workbench and am wondering two things (it 
has a pair of 8873's in it)
>>
>>1.  Is 700 watts output normal for this amp?  Should I replace the 
>>tubes to get - say 1,200 watts or even 1,500 watts output?
>
Low output suggests the possibility of gold-sputtering poisoning the 
emissivity of the cathode.  (see Eimac Letter on my Web site) 
Gold sputtering can be checked for with a high pot. tester.  Use 5kV.  If 
the leakage is more than ten or so uA, it is one possibility.  If there 
is more leakage with the anode pos. than neg., gold sputtering is 
indicated.  However, gold poisoning of the cathode is not necessarily 
permanent.  
>
>1000-1200 W is the safe max and even then keep the heat sink cool.
> New tubes are around $500 each so the choice is yours.
>
 Eimac's  key-down current rating for a pair is 700mA maximum.  However, 
if one tunes up with tuning pulser or with a keyer sending 50+wpm dits, 
the current rating is 1000mA, which you can't see on a meter.   For SSB 
voice operation, the indicated meter reading is around 30% of the actual 
peak current, so 300mA indicated is about right.  .   On a pep wattmeter, 
1000mA peak at 2200v input ought to indicate c. 1300pep.w into a 50 ohm 
termination.  

Rich. Measures.  Web site:  www.vcnet.com/measures


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