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[Amps] 3CX1500D3 Triodes

To: <>
Subject: [Amps] 3CX1500D3 Triodes
From: "Jim Thomson" <>
Date: Mon, 3 Dec 2018 11:07:54 -0800
List-post: <>
Date: Mon, 3 Dec 2018 09:41:49 -0500
From: Bob Maser <>
Subject: [Amps] 3CX1500D3 Triodes

<I acquired a couple of 3CX1500D3 tubes and wonder if I can just plug them
<in.  They are medium mu tubes.  The tube I have been
<running in my homebrew amp uses 3CX1200D7 which are Hi mu triodes.  The
<filament specs are the same and the plate HV specs are
<similiar. My power supply has an output of 4200V which is within the specs
<for both tubes.  Physically, the two tubes are identical and
<the price was right.
<Bob W6TR

##  Nope, wont work.  The MU is too low, being only a mu of 24.  With zero 
bias, the tube will
idle at 1.8 A   at  4.8 kv !     Would require  100 vdc  of bias to get the 
idle current down to  100 ma. 
You would then require one heluva lot more drive to overcome the    100 vdc of 
This is why low mu triodes are not used in GG.  Look at the constant current 
chart at the bottom.
Then u can see where the zero bias line intersects with plate current.   Then 
look again, this time with bias
then u will see how much  bias required to get the idle down to a reasonable 
level.   The tube was designed 
for grid driven, Class C, industrial heating. 

Jim   VE7RF

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