>Hi guys,
>
>I just bought an AL80A.
>All bands are working well at exception of 160m.
>After a quick inspection I founded the reason why:
>The additionnal Plate capacitor (C15 170pF doorknob) is broken and the
>contacts of the rotating connector S1C (both) are completely molten and
>distroyed.
My guess is that the open contacts for the 160m padder were burned by
parasitic arcing c. 150MHz. Photos are available on my Web site.
Ameritron's alleged fix is a "corona washer" - even though the supply is
only 3kV. . The fix that seems to work is a new bandswitch and a VHF
parasitic suppressor with a lower Rp (parallel equivalent resistance than
the original suppressor.)
>I dont know the reason of the failure.
> -Is it due to high VSWR at antenna port?
no
> -Is it due to bad band selection (the previous owner tried to tune
>the AL80A with the 160m bandswitch selection on an other frequency band?
Probably not. When the tank is not resonant, peak voltages are at a
minimum.
> -Is it due to default in conception of the AL80A?
Perhaps. You can find the answer yourself by replacing the toasted
parts, installing a better suppressor (and some glitch protection). If
the mysterious arcing does not reoccur, the problem was parasitic
related. The good news is that the AL-80 is more stable than the SB-220,
TL-922 and AL-82. .
> -Any other idea to explain is welcome
>
>
>I'm looking for any part for their replacement.
>I'll be in Greensborro (NC) for my job in october the 17th and 18th, is it
>possible to find the two broken parts around
>-170pF N750, 850 series doorknob (AR-559)
>-a bandswitch or only one wheel (AR-136-2)
>
>If any store for amps is around there, please let me know.
>If not, do you have any other adress to propose?
>
MFJ/Ameritron is the best source for a new bandswitch. While you have
the AL-80 apart, more than 1000pF is needed for a hv bypass capacitor.
The bandswitch and tank need a cooling fan. A glitch protection resistor
is also needed. The relays need to switch faster to prevent hot
switching with modern radios. - note - After the needed circuit
improvements are made, if the amplifier is ever returned to
Ameritron-MFJ, Mr. Tom Rauch told me that he will order "that they be
ripped out"
>73 de F6HLC
cheers, Christian
>
>
>
>
- Rich..., 805.386.3734, www.vcnet.com/measures.
end
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