[Amps] AL-80A - Won't tune on 160m.

[Vic Rosenthal 4X6GP]

This is a common problem with this amp and the SB-1000 which is similar. 
You don't need to operate on 160m for this to happen. Here is an article 
which discusses the placement of a "corona washer" on the bandswitch to 
prevent this. Make sure you install such a washer when you fix the switch:

<http://www.northland-drifters.net/SB1000Project.htm>

The article also suggests replacing the parasitic suppressor with a 
different type. The original style parasitic suppressor is fine as long 
as the carbon resistor hasn't changed in value or even opened up. I 
would check this resistor and replace it if necessary. The nichrome type 
of suppressor isn't better and heats up more on 10 meters than the stock 
type.

Also while you are at it check the plate RF choke. There were several 
different chokes used in the manufacture of the AL80A and the early ones 
had a series resonance on 17m, which caused them to burn out if operated 
on that band. If the choke is one solid winding without gaps, replace it 
with an AL80B choke that you can get from Ameritron.

73,
Vic, 4X6GP
Rehovot, Israel
Formerly K2VCO
http://www.qsl.net/k2vco/

On 3 Sep 2016 03:11, Bill Coleman wrote:
>
>> On Jun 22, 2016, at 6:56 PM, Bill Coleman <aa4lr at arrl.net> wrote:
>>
>> I managed to fix my issues with the metering circuits on the
>> AL-80A. However, while it appears to work correctly on 80-10m, I
>> cannot get the output network circuit to resonate on 160m.
>>
>> I hooked it up to a dummy load, fed about 35 watts, keyed and tune.
>> Peak output is achieved at maximum C for both Plate and Load, but
>> it’s only maybe 100 watts out, and the tuning is very broad.
>> Nothing like 80m, which works fine.
>>
>> Any suggestions?
>
> I finally got the AL-80A on the bench again and found that the switch
> contacts for the extra plate circuit capacitance are burnt away.
> Since I’ve never used the amp on 160m, this wasn’t me, but probably
> the previous owner.
>
> So, this problem is at least identified. I’ll have to either replace
> the contacts, or the entire switch wafer.
>
> Bill Coleman, AA4LR, PP-ASEL        Mail: aa4lr at arrl.net Web:
> http://boringhamradiopart.blogspot.com Quote: "Not within a thousand
> years will man ever fly!" -- Wilbur Wright, 1901
>
> _______________________________________________ Amps mailing list
> Amps at contesting.com
> http://lists.contesting.com/mailman/listinfo/amps
>