>
>Does anyone have any experience with parasitic suppression techniques for
>valve amplifiers at 70MHz. Note this is not anything to do with HF
>amplifiers etc. The HF methods of supressing VHF parasitics will not work at
>VHF for obvious reasons. This the other way round, how to supress Audio, HF
>and UHF parasitics at VHF.
70MHz is clearly beyond the realm of coil/resistor suppressors. For
stable operation at 70MHz with a tube type amplifier, the Tune-C should
be fairly close to the anode. Based on my experiences, I would use
semi-resistive conductors between the anode and the Tune-C. However,
beyond the Tune-C, high Q conductors are clearly the only game in town.
// In an 8169 amplifier, I seemed to have ok stability by using 4-mil
Ni-Cr-Fe shimstock, cut into a strip about 25mm/1" wide, for all of the
conductors between the anode and the Tune-C. // notes: this alloy has
about 1/40 the conductivity of copper. / The ideal width for such
conductors is whatever will produce a modicum of heating with the
hammer-down. . Mo' efficiency is not always mo' betta. . Better to
dissipate a few extra watts at the fundamental than to raise the Q of the
anode-resonance and risk venturing into the land of parasites.
>
cheers, Mike
- Rich..., 805.386.3734, www.vcnet.com/measures.
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