Ameritron AL-811 Input tune help

[RichardHartman]

I have an older 811 I bought from a gentleman that used it on 11 meter. I open the cabinet and it did not have any of the update / safety mods done to it. I ordered all the upgrade kits from W8JI and a new set of 811 tubes. I tore down the inside cleaned up and added the updates. I noticed that the input tune slugs appear to have been messed with. I have looked at the different manuals and searched the internet and youtube for information on how to service the input tune or even how to properly check the input tune and I haven't found what I was looking for. It's probably so simple and Im just over thinking it.

Is this maybe what I should do?

Radio to swr meter to amplifier to dummy load. While in bypass on the amplifier manually key the relay and tune coils for best swr? Just trying to understand how to check/tune the input circuit. Any help would be appreciated.

73

KC8DVE

 

[AudioShockwav]

A cliff notes version from the web:

The AL-811 has an excellent tuned input circuit easily getting the input SWR down to 1.5 or less. Unless it has been tampered with as might be the case here, Do this. Put an SWR meter between the radio and amp input, connect the amp to a dummy load. Power everything up and put your radio in CW mode medium output key her up and adjust the Amp's plate and load for max output. While keying up check the SWR meter to see what the input SWR is. If it is high over 1.5 adjust the coils to bring it down. Once you do that readjust the plate and load on the amp again, then check input SWR. Keep doing this until you get the lowest input SWR.
I also wanted to add you obviously have to do this for each band.

End Quote
Because the input coils are for more than one band there may be some comprise but it should be good enough to run the amp.
Possibly the 11 meter operator twiddled the 10 meter input tune but that should not effect the other bands.
Maybe he Twiddled all of them?

73
Jeff

 

[RichardHartman]

Thank you Jeff.

here are some pics

73
kc8dve

 

[nomadradio]

The input adjustment is affected by the output tuning. If turning the input-coil causes the power to increase, re-peak the Tune and Load before reading the input-side SWR. Might have to go back and forth between input slug and output tuning a time or two.

73

 

[linearone]

Both responses are correct, also one thing to take note of is that your state of tune will change depending on the amount of drive you apply. So if you tune this thing for one level of power, it'll change a little bit if you lower the drive significantly