[AMPS] Q Swing

[km1h @ juno.com]

On Tue, 19 Aug 1997 23:36:41 -0700 "Ron Angle (AB6ZX)" <dom@shocking.com>
writes:
>Following up on the excellent series "tuning your amp", I wish to 
>present the following scenario.
>
>I am rebuilding a sixties-era homebrew amp running a pair of 4-400s in 
>GG. The power supply is a full-wave, capacitive input circuit. 
>Recently I discovered that the high-low voltage switch on the power 
>supply actually switched between two primary taps labeled 5,000 volts 
>and 2,500 volts, respectively,  for the secondary. I have not yet 
>tested the PS for actual DC output.

Is that a full wave or full wave bridge?  I am hoping it is just a
standard full wave with a center tap. In that case you will have roughly
3500  and  1750VDC at the filter with no load. If that is a bridge setup
it will probably blow the tubes out of the sockets on the high tap.   


>The output circuit is a standard Pi tank with fixed inductor taps on 
>B&W coil stock. The values of  C (tune) and C (load) and the 
>inductance are unknown.
>
>The question: changing the Ep by fifty percent (50%) while keeping 
>most of the other variables constant will  vary the Q and should 
>require retuning.

Not necessarily. With 1750/3500VDC  voltages you may very well luck out 
and wind up with half the Ip in the low position. But why bother? 
Assuming about 3100VDC at a 700-800ma load; you will be at an excellent
voltage for those tubes. Reduce drive if you want to drop power and leave
the rest alone. 

Inductance is easy to determine with B&W coil stock. All you need is the
diameter and TPI and look it up in a B&W sheet. Since the inductance is
linear all you need to do is look up the total L for a  full 10" length
and then measure your lengths.

If the caps have a part #, I or someone can look it up. I also have all
B&W info. 

Hopefully I didnt get too deep!

73....Carl   KM1H

  
 Assuming the Q at one voltage is within the 
>"acceptable" range, should I expect the Q at the alternate Ep to be 
>beyond acceptable with a voltage swing of approximately 2,500v?
>
>Input appreciated; please keep the technobabble appropriate for a 
>geographer...hi!
>73 and thanks to all who contribute to this list...I learn a lot.
> 
>
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