Hi Web-
I am a bit confused by your posts. In the original, you said it idled at 150
watts, but said in the second post you did not have the Hi-V turned on. These
amps are overbuilt, and despite they were set up for 50 watts (AM) from the
factory, I would guess that 150 watts overnight would not be fatal. Anyway, you
stated this problem has surfaced before and it now works.
The relative meter readings you posted seem OK. You did not post what plate
current was when you had no output -- did you have any? And what about plate
current with no drive?
In any event, I have had an AM-6155 for two years for both SSB and FM. With the
original tube, this amp will put out 450 watts on 2 meter FM. I have run this
amp for hours, keyed-down, while duplexing on ATV. The only problem I have ever
experienced during operation is slight output tuning drift after 1 minute or so
of key-down.
For what it's worth:
1) I experienced intermittent power output (but never dead) after the
conversion to 2 meters. The braid of the short coax jumpers that connects the
cavity to the outside world were
corroded where the shield is smooshed inside the N-connector - all of the
connectors were like this. The worst was the custom connector that forms the
output coupling (the one with the RA gear). You must unsolder the access plug
to replace the coax on this fitting; difficult, but mandatory.
2) I assume the filter and directional coupler have been removed; they are only
good for 60 watts or so.
3) Could you have an intermittent t/r relay (dirty)?
4) Someone mentioned it; could the inside of the cavity be corroded? I suppose
the amp could go dead, but it sure would change output tuning to the point of
no, or very low output.
If it only happened after installing the 4CX400, then:
1) Did you slightly bend the fingerstock to the anode? The 4CX400 is a slightly
smaller diameter than the Eimac.
2) Finally, and no offense, did you tune the amplifier after replacing the
tube? When you had no output, did you try tuning? Does it tune at all?
Sometimes the Allen setscrews on the knob or tuning rod couplers come loose.
Web, don't get discouraged. These are great amplifiers for what they cost.
Although I have not performed the 4CX400 mod, it seems like a worthy endeavor
for SSB. With proper bias, that amp should operate (and sound) fine.
Good luck!
John, N9RF
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