[Amps] AL80-B fuse F101 blown;step-startnot working?

[John DiLorenzo]

I acquired this amplifier about two weeks ago, and when I received it,
neither theforward nor reflected power meters would indicate anything. As a
"test", Ireplaced the detector diodes (D114 and D115) with 1N914s as these
were diodes I had on hand.  My intent was to see if the meters would at
least register something, and if so, order the correct diodes (1N34s).
Well that worked,so I ordered the diodes.

They arrived, so I replaced the 1N914s with the correct 1N34s.  With the
unit all buttoned up again, I noticed while tuning up, the meter lamps
would dim, and the HV would sag significantly.  I wanted to test and record
some values when the amp shut down completely; this is what I had to that
point:

  HV
(volts) Ig
(mA) Ip
(mA)  Standby 3050 0 0  Keyed, no drive 3050 0 0  CW, 5W drive 2700 20 125
I discovered that F101 had blown in the amp.  This fuse is in series with
the step start resistor, so it seems my step-start was staying in the "low
current" mode, and when I keyed the amplifier, this 2A fuse blew as
expected.  I'm just not sure what broke.  The diodes I replaced aren't near
the rectifying diodes that pull the step-start relay.  Any insight into
common failures, where to start looking, or how to debug?

Thanks in advance,
John, K8DIL