[Amps] Alpha 87A Auto Band-Switching

[Michael Tope]

I discovered that if you turn the potentiometer R20 in the frequency 
counter portion of the Input T/R PWB (Assy ABX-X182) fully clockwise,  
it disables the frequency counter and auto band-switching that goes with 
it. Assuming the proper load and tune capacitor settings are stored for 
each band and segment, manual band-switching works perfectly and will 
get me by for now.

73, Mike W4EF................................


On 3/2/2026 3:30 AM, Michael Tope wrote:
> One of my Alpha 87A has a problem with the frequency counter that is 
> used by the amplifier to automatically switch bands based on the 
> frequency of the input signal. Normally this is a desirable feature, 
> however, my amp has this problem whereby it will work fine for a 
> while, then the frequency counter will start to malfunction. The 
> counter appears to produce erroneous readings whereby it thinks its on 
> a different frequency than it actually is. This causes the unit will 
> try to re-tune right in the middle of a transmission. Eventually it 
> gets so bad that it renders the amp unusable.
>
> Does anyone know if there is an easy way to turn-off or the disable 
> the frequency counter in such a way that the amplifier won't be able 
> to recognize the frequency of the input signal, but it will otherwise 
> operate normally (with the exception that you would have to select the 
> band manually). I tried doing this with remote control software, but 
> that didn't work. I think that just turns off the auto-tuning whereby 
> it defaults to the stored tuning parameters for the band determined by 
> the frequency counter instead of following the AlphaMax auto-tuning 
> algorithm. Eventually I'll want a proper fix for this problem, but I 
> need to use the amplifier in the short-term, so I need a band-aid that 
> won't involve hours of troubleshooting.
>
> 73, Mike W4EF................
>