BTW, running filaments only does nothing except burn 50 watts. The anode
needs to run at least at a bright red to degass.
When the tube arcs even in the CW position it is usually a hard short but
the only way is to test it at 1000V or less which will not sustain a gas
arc.
Carl
----- Original Message -----
From: "Warren Volz" <warren@warrenvolz.com>
To: "amps" <amps@contesting.com>
Sent: Wednesday, July 12, 2017 2:40 AM
Subject: Re: [Amps] SB220 step start blows fuses
Well I have a major update!
The amp shipped with 2 3-500zs that are “not full output” according to the
seller. Since the amp was in shambles I didn’t have a way to test them
until now.
One of the 3-500zs is unmarked and missing the phenolic spacer below the
glass envelope. The other is clearly labeled as a Eimac. I tested each
tonight with the HV plugged in. The unmarked worked without issue but the
Eimac arced right after turning the amp on!
So, I guess I’m in the market for a new 3-500z. Based on what I see
online, there isn’t really a way to fix this gassy tube but I’m going to
let it sit with no HV and filament voltage for ~30-60 min to see if that
has any impact.
Tonight I also removed the fan and oiled the bearings + the surrounding
fiber. The fan is a lot louder than I expected, but with the oil it’s
slightly quieter.
Thank you all for your help!
-Warren
On Jul 11, 2017, at 6:35 PM, Warren Volz <warren@warrenvolz.com> wrote:
Again thank you all for the advice and guidance.
Replacement fuses showed up today so I'm being a little more
adventurous. As multiple people pointed out the dim bulb tester I have
as built won't work unless I can find at least one 300W bulb.
So, I remove the dim bulb tester and tried each tube in the amp. Good
news is that both filaments light up just fine! To me that rules out the
filament supply and paints a target on the HV supply as many of you have
suggested.
The amp as I received it was a pile of parts, and so I have no reference
in terms of working/not working prior to my mods. Both the QSK and the
RM220 were used pulls off of an auction site. The RM220 is squarely in
my sight now since it had a burned out metering resistor when I got it.
When I checked previously the diodes were all ok. Also, all components
(caps + resistors) on the filtering board are new.
I'll likely try reconnecting the HV primary without the plates connected
to see what that does next.
-Warren
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