[AMPS] B&W 850 in PI-L network

km1h@juno.com km1h@juno.com
Sat, 30 Jan 1999 18:30:42 -0500




On Fri, 29 Jan 1999 17:10:52 -0500 (EST) "William L. Fuqua III"
<wlfuqu00@pop.uky.edu> writes:
>
> I would like to use a B&W 850 with an additional coil w/switch
>to make a PI-L network for my 4-1000A GG amp. I will be running
>5 or 6 KV plate voltage which takes me up past 5Kohms plate 
>impedance.
>The Q of the 850 is pretty high in that case.


It sure is Bill but there is no Golden Rule that says you must use a Q of
12. That is only a ham lore number. The size of the 850 coil and switch
surface indicates that there is plenty of room to play. In practice I
have used that network in a few dozen single and dual 4-1000A amps in
days gone by and the only changes were on the 15M tap and the 10M coil
turns to coincide with the almost minimum C of various vacuum variables.

I would suggest a straight Pi design and do any necessary filtering at
the 50 Ohm level with external filtering. The 4X1 can be squirelly enough
without adding complications.
 
>  Actually, the inductance values seem to work out just about right 
>according to the "Radio Handbook" if I offset the switch by one 
>position.
>That is to make 80 Meter postion the 40 meter one, etc. 

That was part of some late evening 75M QSO's back when the 4-1000A and
the 850 were still popular. As is typical, no consesus was formed and I
never tried it since Plug-n-Play worked for me. I ran 4200-5500V on the
tubes; the customers usually provided the iron.

Also mentioned here several times is that the Irvin Hoff, W6FFC,  ( still
alive??)  article in June 1978 HRM is amongst the best published for Pi
and Pi-L designs.


73  Carl  KM1H


.


>  Is there a problem running the 850 at these higer Qs?
>Does it get HOT? or burn out contacts? If anyone has any experience
>with this please reply. 
>
>73
>Bill wa4lav
>
>  William L. Fuqua III  P.E.  E-mail WLFUQU00@POP.UKY.EDU  Phone (606) 
>257-4155
>  Department of Physics and Astronomy      CP-177 Chem. Phys. Bldg.  
>  University of Kentucky ,                 Lexington, Ky 40506-0055
> 
>  
>
>
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