>
>Anybody have experience with ALC and the grid control board
>in this amp? ALC levels seem to be different for each band,
>making use of ALC as a protective control device useless.
>
? A work-around is to set the transceiver's power output control so that
the 600mA per tube current rating is not exceeded for the band in use.
>In contest situation, quick band change, tired operator;
>just blinking a red light doesn't feel like enough protection.
>
>Thoughts/comments? Recent feedback on the beast, in general?
? The 425 I worked on exhibited - with a Funderberg high-pot
gold-sputtering test, migrant gold damage in both 3cx800A7s. This was
causing B+ arcs between the anode and the grounded grid during signal
peaks. The loose gold meltballs were successfully resetled into the
base of the tubes by hammering on the top of the anode connections with
the flat side of a 4oz ballpeen hammer. Yeah, I know this sounds nuts,
but it worked. To reduce the chance of more gold-sputtering, lower-Q VHF
parasitic oscillation suppressors were retrofitted. A friend on the
East Coast had the same symptons with his 425. He took the amplifier to
Ten-Tec for repair, but they were not successful. He telephoned me and I
told him what I found. He tried better suppressors and the fireworks
stopped. He wrote a letter to Ten-Tec telling them that how the problem
had been fixed. Their reply was that they had read the article about
low-Q VHF suppressors in the October, 1988 *QST*, they tried them but
found they got very hot on 10m, so they chose not to use them.
- If you have access to a dipmeter, please measure the VHF resonance on
either side of the DC blocking cap in ur 425. ¿ Is the dip sharp or not
?
>Doesn't seem to have been much chatter on this reflector in some
>months.
>
? Things slow considerably when our recognized amplifier "expert" is not
participating on AMPS. (p.72, Technical Topics, Sept., 1994, *QST*)
cheerz, Jim Jarvis
- R. L. Measures, a.k.a. Rich..., 805.386.3734,AG6K,
www.vcnet.com/measures.
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