Hi Fernando,
> After making the necessary conections I find out that
> something is wrong. I follow the procedure in the
> manual for cw tunning but things don't go as they
> should (I don't get beyod basic manual procedures
> cause I know nothing about amps):
> 1. HV on standby reads about 3750 volts (manual says
> absolutely no more than 3700)
Check the line voltage and the transformer wiring. While 3750 is
OK on the anode, I would worry about the filament. The filament
transformer has multiple taps. What is your line voltage?
> 2. when I key the exciter (no drive) the plate current
> on the 10000mA scale remains flat- manual says should
> read 75mA. When doing the same but on the SSB position
> the same thing happens (manual says plate current
> sohuld read 250mA).
Something might be wired wrong. Are you closing the antenna
relay and lighting the "XMT" LED on the front panel?
> 3. whatever drive I apply, the grid current remains
> flat.
Same problem as above
> 4. The SWR when I turn the switch from standby to OPR
> goes from 1:1 to abour 3:1. I don't use any antenna
> tuner (I don't need it). This seems odd to me.
You need to find out why the plate current stays at zero, and why
the grid current stays at zero. When that happens, input SWR will
also be wrong.
One cause could be an open filament on the tube. Another could
be a bad solder connection somewhere between the tube filament
connections and the filament transformer, or an open filament
transformer secondary. You should be able to find that with an ohm
meter.
There have been some manufacturing problems with older 8877
tubes, but the new ones made in San Carlos are much better. The
usual problem was a cathode to grid short caused by the wrong
material in the cathode support assembly that also getters the tube.
An open filament is very rare, but you may have one.
If you do have a tube problem, DON'T buy a surplus 8877. Some
are OK, but many are from bad batches. Someone on the west
coast (at Penta Labs) was relabeling bad batch 8877's as new
tubes and selling them, so be careful. The real Eimac tubes have
the Eimac logo embossed in the top. Avoid code dates in the 80's,
and some batches on tubes from the early to mid-90's were also
bad.
> Of course, after seeing these things happening I
> rechecked everything (cables, conections, switches,
> etc.) but found nothing that could explain this. Fan
> works, the 3 minute delay for the plate meter to light
> works, etc.
>
>
> The amp looks clean both outside and inside.
>
> Any ideas why this might be happening?
> The amp has a great price so I would like to give it a
> final chance before returning it. Thanks in advance.
> Ciao,
>
> Fernando
>
>
> ===
>
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>
73, Tom W8JI
w8ji@contesting.com
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