Dave, the ALO boards on these amps are for the most part worthless. They don’t
trip on the important factors anyway. When they go bad I usually just bypass
them. Not worth the effort to repair them unless it’s something obvious. The
LK550 HD as 3 3-500 tubes. As long as your meters are working properly you
don’t need any trip circuits. With the LK800 amps the ALO board has a timer on
it to hold off RF until the cathodes warm up, there it’s a must! But even
still I don’t believe it trips on grid overload. If you are concerned about
real protection most tubes benefit from a simple grid trip circuit which is a
lot less complicated than the ALO board. Some ALO boards do have grid shunt
series resistors that will occasionally open up with tube arcs. They usually
can be seen as bad when inspected closely.
Sent from the all new AOL app for iOS
On Wednesday, November 1, 2023, 5:29 PM, wb0gaz via Amps <amps@contesting.com>
wrote:
Thanks (Dave) for insight on the panel meters.
Arriving to the point (on LK550) that the ALO/Meter board is suspect - either
was damaged or caused damage in it's prior life. Several traces handling 12V
path were badly overheated, one to the point of destruction, and the board
(with a couple of previously added jumpers to bypass two of the smoked traces)
is still dragging the 12V DC control power supply (simple half-wave rectified
off the low voltage transformer) down to near zero when amplifier is enabled
(XMIT on the XMIT/STBY switch.)
Now intend to delete ALO/Meter and rewire as if it were a LK500 or other model
without ALO/Meter (hence why I wanted to understand the nature of the two panel
meters.)
Next step is to find pair of nylon 6-pin connectors (equal to what are
currently on the ALO/Meter board); they are physically polarized and a search
through digikey hasn't found anything equivalent so far. Although could remove
the connectors from the (suspect) ALO/Meter board, would rather set it aside
as-is for now and source replacement connectors (on the PCB, the two connector
housing are female, and the (6) pins are male.) My supply of pins doesn't
include any that are the same dimension as the one used on the PCB (else I'd
just stuff equivalent pins into the needed positions on the end-of-wire
connectors and call it a day.)
Thanks again for the hand-holding through this saga!
Dave
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