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MODIFICATION OF R-140 LINEAR AMPLIFIER

IMPROVEMENTS OF TETRODE GU-43b OR Q-1P/42

OUTPUT PI NETWORK

by F1FRV

Rev 3:  November 2006  New pictures & measurements results

Rev 4:  March 2014   New arrangement for higher power in low bands.

After testing and checking of original circuit, idea was to modify arrangement of capacitors in the amplifier output PI network. As power output (with same input) was measured ridiculously less in low bands than in higher bands (sometimes, impossible to match in low bands), some additional mods have to be done. This in order to have better results on all ham bands.

Spectral purity after modification measured in all bands is excellent.

Measurements and curves of the modified amplifier

The modifications are quite simple.You will have to modify the contacts arrangement in the 5 positions rotary band switch, and modify fixed capacitors arrangement.

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EXCEL spreadsheets APPROXIMATIVE calculations. Results are not perfectly accurate, due to the variable parasitic parallel capacitance of the variometre L2, impossible to take into account here .. Nevertheless, it works....

WORKS HERE WERE REALIZED ON NEW MODEL 6M1

The 5 bands rotary switch ( "Trommel" ) and modifications in band 2

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Fixed capacitors arrangement

The new 20 pF 10 kV capacitor & new placement of the 12 pF

Download modification documents: PI GU43b MODIFICATIONS.zip

Link to R-140 amplifier main page

Dominique - f1frv@sfr.fr OR

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