Kent:
If you can find a replacement bandswitch with SHORTING contacts I
would think your problems would be solved. I experienced some bandswitch
arcing (Radio Switch #86) on my 8877 amp.
I operated my amp on 160 - 20m, didn't even have a 15 or 10 m band
switch tap until I wanted to work the P5. My old 3-500Z's were not doing
the job with the big pile-ups. So I added the 15m tap. It was then and
only then that I experienced bandswitch arc. I added a short jumper
with alligator clips from the 80m to 20m taps and eliminated the
problem. Of course the jumper comes off and I'm back on 160 through 20m.
One of these days I'll spend the big bucks and add a shorting model 86
and permanently fix the problem.
Dennis, w8nw
2 wrote:
>
>>A ham friend of mine asked me to troubleshoot his newly acquired but
>>inoperative AL-80A amp. yesterday. The first problem I found was the
>>antenna relay had been hit by something, knocked out of position and
>>bending the contacts.
>>
>>This was relatively easy to fix, but after that, a continued visual
>>inspection revealed that 2 of the 3 wafers of the band switch had
>>several vaporized contacts.
>
>
> This is usually the result of an intermittent parasitic oscillation c.
> 155MHz. Does the toasted bandswitch look like the AL-80 bandswitches at:
> http://WWW.VCNET.COM/measures/bandsw.html
> ?
> One solution is to trade the new, high gain tube that apparently
> oscillated for an old worn-out tube with lower gain that couldn't
> oscillate if you wanted it to. Wanna swap tubes? An alternative would
> be lower VHF-Q suppressors.
>
>
>>My next step will be to replace the
>>bandswitch, but now I am beginning to wonder if there may be a high
>>probability of other problems present that caused the extreme arcing of
>>the bandswitch. I have looked in the archives and see the info about vhf
>>parasitics as a potential problem, but are there other known problems
>>that I should look for ?
>>
>
> The burst of grid/cathode current that accompanies a vhf parasite
> creates an EMF that can bend the hot (1820?K) filament perpindicular to
> the flow of grid current. With repeated parasitic events, the tube may
> short. With a high-pot tester, a healthy tube will exhibit a
> withstanding potential of 5 to 8 kV. Also, metering damage is possible.
>
>
>>Also, is the bandswitch in the AL-80B interchangeable with the AL-80A
>>and are they still available from Ameritron ?
>>
>
> Yes, and for a reasonable price.
>
> cheers, Kent
>
> - R. L. Measures, a.k.a. Rich..., 805.386.3734, AG6K,
> www.vcnet.com/measures.
> end
>
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