[Amps] 3cx3000a7 HV

[Jim Thomson]

Date: Fri, 18 Nov 2011 03:37:14 -0600
From: e73m at e73m.com
Subject: [Amps] 3cx3000a7 HV

Hello,

does anybody know would it 3cx3000a7 work at 3500V for plate (under 
load) in order to use air capacitors in PI tank?

Goal is solid 1500w out with 100w drive.


Thanks, Danny E73M

##  good question.  With 4.8 kv under load, the 3x3 will do an easy 1500 watts out with just 50 watts 
of drive. [150 ma of idle current].   With 100 w of drive and 4.8 kv it will do an easy 2.5 kw out.
150 w drive = 3.5 kw.   200w = 5.2 kw. 

## OK, on paper, with  3.5 kv [ under load]  and  100 watts of drive it should do   1250 watts out. 
 So you end up short.  If you had more drive, you could get your 1.5 kw.  I have never seen this tube
operated with less than 4 kv on it.  Never seen one with out a vac tune cap in it  either  [ with the sole exception
being the henry 8 k ultra, which used a myriad of solenoid operated  doorknobs].  The 8 k used the roller coil
as the "tune control"    The vac  load cap in the 8 k was a small 500 pf @ 5 kv thing..which was also heavily padded.
The modified solenoids just grnded the cold ends of  both the tune cap doorknobs and also the load cap padder's.
That way, no conventional tune cap used at all.  The exact amount of doorknobs for each band was switched in.
On 20m, they used a single 25 pf @ 15 kv HT-57 cap  [ HEC brand].   Above 20m, no cap was used at all, since the
3x3 tube already has 24 pf of anode to grid C.... plus once into the socket,, it rises to 33 pf, due to the proximity of
the lower anode fins to the chassis.  

## To keep the plate load Z  reasonable, you don't want to operate it with high B+  and real low plate current. 
With  only 3.5 kv.... you can reduce the bias a whole bunch, which will make it a little easier to drive, still, the gain
has dropped a lot with the 'low'  3.5 kv B+.     I'd say you will either get ur 1.5 kw, or very close to it.

Later... Jim   VE7RF