[Amps] AL-572 high input SWR

[R.Measures]

On May 9, 2004, at 6:46 AM, K4RO Kirk Pickering wrote:

> A friend has asked me to look at his Ameritron AL-572.
> The amp quit functioning about 7 months ago, after two
> years of dependable service.  The amplifier was used
> almost exclusively on 17 meter SSB. The symptoms are
> as follows:
>
> Very low output - 100W on 20m-10m, 300W max on 160m-40m

Kirk --- Low output in 10m can be caused by a missing 10m contact in 
the L-tap section of the output bandswitch.
>
> Very high input SWR - > 3:1 on all bands, over 5:1 on 17
> meters. This is the SWR the radio "sees" looking into
> the input of the amplifier.
>
> My first guess was that a component (which is common to
> all bands) on the tuned input  circuit has smoked. A
> quick visual inspection does not reveal any burned parts.

Higher than normal input SWR with a multi-tube setup can be caused by a 
tube with an open filament.  I have seen this in an AL-811.
>
> Before I go digging deeper, does anybody have any
> experience with this amp or suggestions on what may
> have failed?  Thanks for any assistance.
>
> -Kirk  K4RO
>
>
>
Richard L. Measures, AG6K, 805.386.3734.  www.somis.org