Hi Chris,
> Hello all
>
> I've looked through the archives and can't see much about the AL-80.
> I've just purchased an early model AL-80 and would like to modify
> it/upgrade it before using it.
>
> I know that there were some parasitic oscillation problems with these
> early models - can anyone tell me how the AL-80A and AL-80B have been
> improved ?
I never heard that rumor about early AL-80's, except from Rich
Measures. He attributes any failure, no matter what the actual
cause, to parasitics.
If you feel more comfortable, make mods...but they won't cure
problems that aren't there.
The bulk of failures in early AL-80's (made by Amp Supply prior to
Prime Instruments recalling the line do to a bad debt) were:
1.) 1/8 watt 250 volt rated resistors across the diodes.
2.) Wrong input circuit values
3.) Too much tank Q on 160
4.) Jennings door knobs (200 pF) across the tuning cap caused
drift on 160, they need to be replaced with 170 pF HEC and the
tank coil made larger
5.) Carbon resistors across the electrolytics that were dissipating
over 2 watts in a two watt resistor
6.) Inadequate air flow across the tube, and poor air flow system
design This resulted in tube seal failures and tube arcing.
7.) A QSK system that never worked. Denny Had copied it from a
Heathkit two meter amplifier never understanding it used 1/4 wave
lines at two meters and wouldn't work on 160 through ten.
You can tell if your unit was one of the "Amp Supply" AL-80's by
looking at the serial number and meter scale, and looking inside at
the components. If the meter has a two scale face, only volts and
single ampere scale, it one of the Lemon units. Ameritron bought
most of them back and rebuilt the others at no charge, but that
program has long expired. Any AL-80 above S/N 350 is OK.
Personally, I'd avoid the AL80 and try to find an 80A or 80B model.
73, Tom W8JI
w8ji@contesting.com
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