[Amps] Tank eff.. with more B+

[Jim Thomson]

Date: Mon, 15 Feb 2010 08:28:31 EST
From: TexasRF at aol.com
Subject: Re: [Amps] Tank eff... with more B+
To: Jim.thom at telus.net, amps at contesting.com
Message-ID: <2d55.3ebd8eeb.38aaa5ff at aol.com>
Content-Type: text/plain; charset="US-ASCII"

 
Hi Jim, I will rephrase a bit.
 
I used peak power in the efficiency numbers and should have used rms power. 
 My bad.
 
Assuming the plate current is 1A for both examples, low power would  
generate 2200w peak, 1555w rms with a d.c. plate power of 2700w and  efficiency is 
57.6%, high power would generate 3000w. peak, 2121w rms with a  plate power 
of 3500w and efficiency of 60.6%. The difference then is 3% more  
efficiency. Again, this is for the tube only, no tank losses.

## which is abt what I see  toggling between  625 w and  1290 w
, when switching B+ on a L4B .  Plate load  Z stays the same,
and so does the loaded Q 


  
Well, the plate tank circuit does have loss. Assuming you use the same  
band switch position, the plate inductor is the same one for high power and  low 
power. When you tune the tank circuit for maximum power out, the current is 
 higher with the higher plate voltage because the amount of power is 
higher.  Higher power comes with higher voltages and inductor current rises as a 
result.  Another way to say this is that the loaded Q is higher.

## agreed,  but if u increase the plate current by the same %,
plate load Z stays the same.. and so does the loaded Q. 

   
The above example would imply an unloaded Q of 78. If this Q was improved  
to say 200, then the loss at low power would be 78w , power out would be 
1477w  and efficiency of 54.7%. At high power Q=13.63, loss is 145w, power out 
is 1976w  and efficiency of 56.5%. The difference in efficiency being 1.8%.

##  use either bigger tubing for 10m.. or better yet, wide, flat strap,
wound flat...[ like a suppressor]   Strap coils will conduct RF  on BOTH
sides of the strap, and C between  adjacent turns is zip. 

## use a tiny bit of uh  b4  main tank coil [ or center tap the
existing 10m coil with the hot end off the tune cap].. and loaded
Q on 10m will drop like a rock = cooler running tank coil.  Un loaded
Q's  well above  200 are achievable



  
All of the commercial amplifiers with high/low voltage switching were  
intended to tune on cw to establish a plate power match to 1kw power input and  
that would produce maybe 550 to 600w output. Then upon switching to higher  
voltage, the tuning was left untouched for a corresponding increase of plate 
 current that produced the same load impedance. If the voltage is increased 
 by 44% and the current by 44% then the plate load impedance remains the 
same and  power input and output is doubled.

##  agreed,  it's actually sq root of 2 = 41%.. moot point.  Double
or  1/2  the plate V.. [ and ditto with plate current].. and power
goes up/down  6db. 


Anyway, all this was in answer to "why would efficiency improve with more  
B+". This is why. Think of the higher% plate voltage swing.

## yes, you are correct, I'm glad you pointed that out.... and the
constant current charts prove it.  They all flip up a bit at the bottom.

take care.... Jim  VE7RF

 
73,
Gerald K5GW