>
>Well, at the start of the CQWW CW Contest, my SB-220
>smoked. One of a near new set of Eimac 3-500Z's developed
>a grid-cathode short and smoked the grid bypass choke.
>After some research, it appears that this is a common
>failure mode of a VHF parasitic. I will be changing
>the parasitic suppressors out but I am also considering
>strapping the grids directly to the chassis. I assume
>that a mod is also needed in the grid current metering
>circuitry.
>
>My questions:
>Have you done a directly grounded grid mod to your SB-220?
Yes, however, the grid-resonance moved only a small amount. I reversed
the mod so that I could use grid fusing resistors.
>Did it do the job of stabilizing the amp?
The amplifier was apparently stable either way. At the time, I was using
lower VHF Q parasitic-suppressors.
>Any additional mods required (grid metering, etc.) ?
>
No metering modification is needed.
cheers, Mike.
- Rich..., 805.386.3734, www.vcnet.com/measures.
--
FAQ on WWW: http://www.contesting.com/ampsfaq.html
Submissions: amps@contesting.com
Administrative requests: amps-REQUEST@contesting.com
Problems: owner-amps@contesting.com
Search: http://www.contesting.com/km9p/search.htm
|