> I am attempting to repair an AL-811H for a friend. The amp has been
> abused due to mishandling as aircraft baggage making several trips to the
> Caribbean and back. The outer case shows several dings and one of the
> threaded holes in the chassis metal which holds the cover in place has
> been broken open.
>
> The reported symptoms are: When attempting to tune the amp upon return to
> home QTH, there was a pop and a flash inside the amp.
>
> ::Sounds like someone took a picture. Did you pose?
>
> On my bench, I am driving the amp using an Icom 751-A. The only visible
> signs of damage evident to any of the electronic components was one of the
> two 1000pF DC blocking capacitors from the anode/plate RFC to the tank
> circuit was cracked open slightly. I replaced these with two 500pF (6KV)
> capacitors for test purposes with no apparent difference in result. Using
> an ohm meter, it appears that the DC input blocking capacitors at the top
> end of the filament RF choke are good and that no short circuit to ground
> exists on the input. The tubes show no internal shorts using an ohm
> meter. The tubes light properly, the HV is 1700V and the anode idling
> current when keyed (without drive) is 150 mA (which is about right).
>
> I disassembled the rear pc board from the rear panel and inspected the
> traces for burns and shorts, but nothing was obvious.
>
> When attempting to operate the amp, the grid current and plate current
> swing up and down in synchronism with the drive, but NO RF output is
> observed. I am using a power meter and a Bird 2500 watt dummy load.
> Adjustment of the TUNE and LOAD capacitor produce no apparent dip nor
> power output. No unusual smell or noise is observed.
>
> ::This really sounds like a T-R relay not making contact, or possibly not
> even switching. I don't recall if the AL811H has a separate input relay
> and output relay, or if they're all one unit; however, the symptoms seem
> to indicate an open circuit between the plate tank and the coaxial output
> receptacle...
>
> Any suggestions would be greatly appreciated.
>
> Dave, WT8R
>
>
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