Re: Amp Supply LK800 Meter/ALO Board Question
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Plate/Grid flash over.?
With a manual tune amplifier, a likely suspect is a band change and failure to tune the plate and load at low power.?
Another way is returning to from a break in operation then upon return switching bands or switching antennas without retuning the amp¡ªwith Steppir antennas this is an easy mistake to make. Specially when you have automatic antenna selection from your
rig to the antenna switch and/or automatic band selection to the Steppir.
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The worst thing for a shack is to have a manual operation set-up required in an otherwise fully automatic switching shack from
a modern transceiver.
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73,
Dave, w6de
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From: [email protected] <[email protected]>
On Behalf Of Mark KE1IU via groups.io
Sent: 26 November, 2024 23:24
To: [email protected]
Subject: Re: [ham-amplifiers] Amp Supply LK800 Meter/ALO Board Question
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All-
I gave the amplifier a try tonight at very low drive, slowly working my way up to legal limit to ensure the meter did not peg to the right due to an incorrect resistor value.? Everything seems normal (grid current of ca. 30 mA when tuned,
and turning the load control clockwise reduces it), so that resistor R29 is indeed 18 ohms.? If anyone knows why that might have?blown, I would?be interested in your thoughts.
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The PDF file here works for me.? I have seen this manual before.? It has no information on the ALO/metering board.? Yes, there are two meters in the schematic, but my LK800a does not have the same wiring of those meters.
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I have an Amp Supply Company LK800A amplifier that puts out full power.? However, I noticed recently that it shows no grid current reading when transmitting on multiple bands.? This is odd behavior, as the grid current normally runs ca.
20-50 mA from my past experience.? I know the meter is fine, because when I turn the meter switch to measure plate voltage, I get the expected reading.? I looked at the meter/ALO board and found that R29 was somewhat charred and had a reading of 180 K ohms.?
No other parts look visibly damaged.
The LK-800 series manual does not have a schematic for this board.? I was able to find one at
.? While the manual is for the LK-400 / LK-500 series, it does have a description of the ALO/Meter board.? The resistor R29 is in the grid current metering circuit and
is claimed to have a value of 18 ohms (p. 27 and 29).? I suspect this is the problem.? The other parts on my board seem to match what is listed on p. 29, and the parts list on p. 29 suggests the board works in the LK-800 series amps because it references the
heavy resistor R30 as being unique to the LK-800 (and is present on my board).
My question - can someone verify that R29 should indeed be 18 ohms?? I would hate for there to be a misprint in the manual and find my grid current meter to be blown when I try this out, as I suspect they are very difficult to obtain.?
Also, do you have any insights as to what would blow this resistor?? A current of 120 mA through that resistor would deliver 0.25 watts...? I have always kept the grid current low, but I did loan the amplifier out a few years ago and don't know if the other
user experienced an issue.
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