Shaking that tube probably caused some loose metal to generate a dead short.
Carl
KM1H
----- Original Message -----
From: <johndtate@post.com>
To: <amps@contesting.com>
Sent: Monday, April 12, 2010 3:19 PM
Subject: [Amps] Henry 2K4 troubleshooting
> Remember the Henry Hum thread(s)? Your help on that issue was greatly
> appreciated. Several people chimed in and the answer ended up being in
> a poorly designed filament choke. The stock filament choke was wound
> on a toroid but it was NOT bifilar wound. Each lead was wound
> separately on opposite sides of the toroid form, not interlaced in a
> bifilar fashion. I replaced it with a conventional bifilar wound rod
> type grounded grid filament choke and that took care of the hum.
>
> Now after enjoying the amplifier in mostly AM service, it has developed
> some more issues. Following a bad "squeal" that seemed to be coming
> from one of the 3-500Z's I decided to investigate a bit. This problem
> was intermittent but it scared the hell out of me. I wasn't sure If I
> was seeing any flashing or arcing coming from the rf deck but then
> again, I didn't wait that long to unkey. Reducing the drive a bit and
> rekeying seemed to bring everything up normally. But it happened
> another time a couple nights later and so I shut it down and proceeded
> to pull the rf deck and investigate any visible signs of stress or
> arcing. I should add that when previously observing the pair of
> 3-500Z's while keying up in what seemed to be a functioning amp, I
> noticed one of the tubes showed quite a bit of color only ONE side of
> the plates. Subsequently, I see that the inside glass on that one tube
> has darkened on one side, the side that the plate was showing more
> color.
>
> See
> http://www.flickr.com/photos/79319481@N00/4515561628/in/set-72157623715944749/
>
> I'm afraid that tube has led to my problems, as I can hear a springy
> sound when I handle it, as if something has dislodged inside. I missed
> this during this initial checkout and put everything back together
> after looking at the undersides of the sockets and my filament choke to
> make sure there wasn't something going on with my previous filament
> choke replacement but all seemed normal. So I put everything back
> together at that point, re-installed the pair of tubes and zipped it
> all up. When hitting the on switch the blower and panel lights turned
> on, but no output when keying... hmmm... looked inside and notice the
> filaments were not lit.
>
> I then reseated the pair of tubes for grins but this time... BOOM...
> overload relay tripped. Reset the overload relay and BRTTTDD
> BRTTTDD... heavey vibration for split second and the 15 amp circuit
> breaker (built into the amp) tripped with the overload relay.....
>
> Following the troubleshooting diagram.... determined at this point
> there was a HV short in the power supply. (The 15 amp CB keeps
> tripping even without the HV plugged into the rf deck now.) Found one
> "diode" in the FW Bridge rectifier to be shorted. The FW Bridge
> consists of two HV rectifier blocks where each block represents two
> diodes in series with 3 leads. With the rectifiers out of the
> powersupply, she powers up without tripping and I do have filament
> voltage at the sockets.
>
> Looks like I'm needing a couple of replacement HV rectifier blocks and
> some new 3-500Z's. I'm not understanding how a filament problem would
> have blew the diodes in the bridge, since the filament voltage comes
> from the filament windings on a separate secondary from the plate
> txfrmer.
>
> My line voltage is 242 volts not 220. The amp is indicating 3400 volts
> on the panel meter and 3200 volts under a load. Should be fine but I'm
> concerned about the filament voltage which is showing 6 vac instead of
> the target 5 vac. (Checked with a VOM at the empty sockets.) Could
> that have been the source of my sorrows? I sure don't want to spend
> the bucks on the HV rectifiers and a new pair of tubes only for all
> this to occur again after a couple months.
>
> Any thoughts and tips would be greatly appreciated!
>
> 73, John KX5JT
>
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