I agree with Vic, try type 6 material for the core.
The input of the GS-35B appears to be higher on 10 meters and may be on
the order of 90 Ohms. These values have been used with success on a
single tube: Cin = 100 pf, L = 0.02-0.08 uh variable, Cout = 180 pf.
Be sure your RF is connected to the larger diameter connection which is
the one that has the cathode connected directly to it. Also use a
separate cathode choke to feed B- instead of the filament transformer
center tap.
73, Tony W4ZT
Mike wrote:
> Hello,
>
> 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.
>
> Details:
> The input network was designed using the spread sheet pi calculator
> by Phil, VE3OZZ, with the following entered parameters; Freq. =28.3
> MHz, Q=2, Rin=50 Ohms, Rout=30 Ohms. The 30 Ohms was derived from
> review of the archives on GS-35B input impedance and from the
> equation Eg/(Ip+Ig) where likely operating parameters would be Eg=30
> V, Ip=0.8 A, Ig=0.2 A.
>
> The spread sheet produced the values of C1=142 pF, C2=139 pF, L=0.22 uH.
>
> L was wound on a T68-2 with six turns of number 18 gauge wire. The
> six turns was calculated using Amidon information.
>
> The circuit was assembled on FR4 perf. board with a 30 Ohm
> composition resistor across C2.
>
> The pi-network was tested with a MFJ259 connected across pi network
> input, C1, by ~3 feet of RG58.
>
> The circuit didn't work as the resonance was ~26 MHz.
>
> C1 and C2 were adjusted for a minimum SWR (~1.1 : 1) at 50 Ohms on
> the MFJ259 at 28.3 MHz. The values for C1 and C2 are, respectively,
> 130 pF and 80 pF.
>
> 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.
>
> The xcvr connected and amp. turned on. When the amplifier was keyed,
> the xcvr registered a SWR greater than 3 to 1 at 28.3 MHz. No
> resonance was seen by a dip in the SWR reading in the xcvr over the
> 10 meter band.
>
> Okay, where did I go wrong in my thinking and/or implementation?
>
>
> 73,
> Mike, K4GMH
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