Folks,
Thanks for the on & off list replies. I'd
checked out the push switch, resistors
relating to the grid & ALC circuits. All
were fine in the CB-2 Control board. All
the caps were WNL. The diodes were all
responding normally except D211 which
offered a beep in each direction with the
DVM so I was on the right track
Removed the diode and it was fine out of
the circuit but it shouldn't have done
that so looking at the 2N304 transistors,
rather than test each one with the DVM, I
just pulled and replaced them. Since I had
the board out, I replaced Q202 (MJE802)
using a liquid metal thermal compound for
better heat transfer instead of the
original paste compound), I'd already done
that with the 24V regulator a few months
back. 2nd step was replacing Q203 (2N3904)
as that diode connects to 203's base,
retested the diode and it now properly
only passed in one direction.
I assume that was the only problem but as
mentioned, I replaced all the inexpensive
2N3904 transistors related to ALC & Grid,
put everything back, fired her up and now
the ALC works as expected and the grid
current is reading properly as well.
Yesterday when I did the sleuthing &
repair it was my Birthday, so fixing it,
'twas a nice present I gave myself. :)
Thanks again for those who offered
suggestions.
73,
Gary
KA1J
> The day before Thanksgiving I was
> listening on 160 & lightning hit close to
> the antennas. Heard a sizzle in the shack
> and lost a few things. Guess Polyphasers
> in the coax and a good ground isn't enough
> to dodge the bullet.
>
> Among the things damaged were the LP-100A,
> the P3 Wattmeter, Computer BIOS, GPSDO and
> now I find the grid metering is not
> working on the Alpha. When putting the amp
> to the load/tune settings I have written
> down, it performs normally and my signal
> report was 59+ with excellent audio.
>
> All the other meter functions are working
> as before but not the grid metering. When
> I transmit the grid goes to .7 MA and
> stays there unless I increase the input
> power significantly and then it raises.
>
> Adjusting the load does not affect the
> meter but if I increase the load out of
> limits, the ALC meter does light and then
> goes out when I back off the load. It
> appears the ALC is still intact.
>
> I'm not enough of an engineer or tech to
> adequately understand the schematic, but
> looking at circuit board CB-2, the control
> board, I see Q202 & Q203 as well as a few
> diodes are in the metering path. I have no
> way to test the transistors but they are
> inexpensive enough I can just replace
> them.
>
> I made a 3 page PDF of the schematic for
> the push switch for grid and the control
> board.
>
> http://doctorgary.net/grid-circuit.pdf
>
>
> The entire pdf manual is here at Alpha RF
> systems
>
> https://tinyurl.com/sndumoa
>
>
> Any suggestions for what I might check
> would be greatly appreciated.
>
> 73,
>
> Gary
> KA1J
>
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>
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