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AF6LJAug 2, Hopefully it didn’t smoke the a-l811h Any suggestions would be welcome. AF6LJAug 1, Arcing is a momentary short flashover in one of the transmitter tubes.

What a horrible linear amplifier!


You must log in or sign up to reply here. I haven’t confirmed this yet, as it’s really hard to get at the main board to test anything! Many thanks for that Glen.

The size of the 10 m coil has become manyal small due to mounting method. Connect the amplifier to a dummy load and adjust for maximum ouput. In reality, no way to predict how the circuits actually behave.


ALH Modifications

la-811h I don’t know what they were thinking. The energy could not leave via the high impedance of the plate circuitand so chose the shortest path via the tube.

On the other bandthe SWR will be high and is an internal tuner required for full ouput. I’ve just been asked to fix an ALH by a local.

ameirtron That ‘s nothing compared to a deceased tubediodes, or worse a faulty transformer. Test and adjust the SWR also on the other bands.

Irregularities in the schematic. However, it’s as if the Valves are getting no drive on Transmit. I wouldn’t supersize that diode, it is a weak link mabual a reason as I understand it.


I’ve never seen one before. I can hear at least one of the relays going over, but the SWR into the amp is very high. K9STHAug 2, If the PA is not used for a long time and goes back into operationremove the fuse and let the amplifier an hour long stand idle. No the meters are both OK.


I think it had a Valve flashover before I got it. A tentative conclusion is that this AL – H does not distort the signal of the drive stage. I believe it’s asking for troubleand it is better ameditron shorten the RF path by installing an additional 4n7 capacitor at the lower end of L4.

It is a cheapsimple and proven effective method. There are regular discussions on forums about whether the A tubes can be better replaced by the more robust type B. I am wondering why you say the amp is awfully made. The PA had no additional protection and had not been operational for years.

I’m guessing it was designed at the Christmas party and they were all drunk. Ql-811hAug 1, After each modification the amplifier was firmly tested and plates never becames red.

The shielding of the cable is only grounded at the ameritroh of C