Ameritron AL-811 Tuned Input Optimization

[N8BOS]

The manual for the Ameritron AL-811 (3 tube) HF amp indicates that the slug-tuned input coils for each band accessed thru holes in the rear panel are adjustable for best "optimization."  How do I know if I need to adjust them and if I do, how do ya do that???  The manual offers no hint of a procedure to follow. Thanks for any advice.  Bill, AB0ZZ@ARRL.NET

[NI0C]

Check an SWR meter (your transceiver probably has one) that indicates the SWR of the match between your transceiver and the amplifier input (with the amplifier keyed).  If the SWR is 2:1 or higher, your (presumably) solid-state finals in the transceiver may reduce the drive power to your amplifier.  In this case you may need to adjust the tuned input coils in order to get all the drive power to your amp that you need.  This usually won't be a problem on say 80m or 40m; however if you wish to operate both 15m and 17m (or 10m and 12m) where you have a single bandswitch setting for both bands, your adjustments to improve things for one band may make things worse for the other band.  In this case you may need to come up with a compromise setting.  If your transceiver has an auto-tuner feature, try using that in lieu of adjusting the coils.  

73 & GL,

Chuck  NI0C

[K8AC]

Take a look at the SWR that the transceiver sees when feeding the amplifier.  If the SWR is excessive on any band or portion of a band, you might want to tweak the input coil for that band. A better way to do this is with an analyzer like the MFJ-259B in place of the transceiver.  If you use that approach, don't forget to key the amplifier relay so the analyzer is seeing the input network and not the antenna.  I don't know how the AL-811 input is designed, but I assume it's like some of the other Ameritron amps (AL-80B, AL-800H) where 20/30 meters shares a common input coil as does 15/17, and 12/10.  In that case, you'd want to adjust for an SWR as low as possible on the two bands.  Unless the input SWR is high enough to cause your transceiver to fold back the output power, there's probably no reason to fiddle with the coils.  If your transceiver has an internal tuner, you can always turn that on to reduce the SWR to a low value anyway.