[Amps] input circuit design problem TSPA

John T. M. Lyles jtml at lanl.gov
Wed Jan 18 11:20:39 EST 2006


The 30 ohm input Z may be suspect.

One more thing, (probably not related to your circuit problem) I 
noted that you are using 0.01 mica capacitors across the filament and 
as blocker. Have you verified that the caps you used (with the lead 
lengths) are not self-resonant at or below your operating frequency. 
This could screw up your circuit performance. Maybe measure one with 
a dip meter, impedance meter or the like? If thise micas don't bypass 
the 2 filament leads well, you might consider ceramic chip 
capacitors, the ones with flat leads for stripline mounting. Or 
change the value of the micas until they really look like a good RF 
short at your freq.

73
John
K5PRO

>An attempt was made to hook-up single 10 meter a pi-network input to
>a GS-35B.  Unfortunately, it didn't work although seemed to check out
>okay on the bench and when it was installed in the amp on  the bench.



>The pi-network C2, less 20 pF to compensate for the tube's input
>capacitance, was connected to one of the GS-35B's filament
>connections.  L was attached to the same point on the filament and C1
>and the 0.01 uF mica blocking capacitor to the other end of L.  A
>similar 0.01 mica capacitor is connected between the filament
>terminals.  A 30 Ohm resistor was connected across C2 and the MFJ259
>connected to the free end of the 0.01 uF blocking capacitor.  The
>circuit checked out okay.  The filament choke was connected to the
>filament connections when the measurement was taken.  The 30 Ohm
>resistor and MFJ259 were removed and the RG58 cable from the input
>relay was connected to the 0.01 blocking capacitor.


>          73,
>          Mike, K4GMH



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