>I have an sb 1000 converted to six meters that is definitely oscillating
>it still uses the 3-500z but after reading Rick Measures web site I see
>now that the
>anode supressor that was built was not going to supress much. It was an
>1 turn copper coil and 10 watt 37.5 ohm resistor network consisting of 2
>75ohm resistors, one inside the coil and one outside the coil. When the
>amp went into oscillation (i think partially due to a combination of an
>bad zener diode
? Typically, zeners go bad (short) during a VHF parasitic oscillation
due to the surge in grid-I.
>and me playing with the input pi network tuning cap) it
>blew the outer resistor only.
>the inner was spared.
>I now want to try to get this amp to be stable but all the reference
>material I see on the net or in the ARRL HB deals primarily with 3-500z
>tubes in HF amps, not on 6 meters. I know I had other problems ( maybe a
>dead tube or the Zener) but I want to
>at least give the tube a fighting chance. Also is a good test bed for
>including the henry amp that needs a similar upgrade.
? I have two ideas for perhaps improving the VHF stability.of the
3-500Z: 1. Add a VHF snubber from the cathode to ground (R-C-L series
circuit). 2. Build an all Ni-Cr anode lead to decrease VHF Q at the
anode resonance (usually c. 150MHz.. My guess is that these
modifications may cost a 5% power decrease at 50MHz, but they may make
the amplifier stable. If you are willing to have a go at this, give me
your telephone number and a suggested calling time so that we can discuss
it. Or, you can telephone me if you like.
- cheers, George
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