Not necessarily, but you need to bring them up carefully.
If you have or can get access to a hi-pot tester, that might be the best
first step.
However, if it were mine:
1. Remove one of the tubes so you aren't trying to deal with two at a time.
2. Run filaments only for 3 to 4 hours.
3. Bring plate voltage up slowly (you will need to get a variac connected to
the HV primary so filaments will stay hot. Also, you should put a non-slow
fuse in series in case it decides to flash over.
4. When you get to a kilovolt or so, carefully apply some drive gradually
bringing it up (obviously you need a dummy load here that can take the power
for a period of time)
5. Bring up drive watching plate current carefully.
6. If it arcs, back down and repeat. One thing I have learned is that if
the tube arcs without destroying the grid or filament, the arc will have the
effect of cleaning some of the gas out of the tube (I know this doesn't make
sense, but years of bringing up really big tubes that were gassy has
confirmed this). The fuse is very important here to prevent damage to the
tube and the power supply.
6a. If it continues to flash over after a few tries, you might want to
consider that tube a lost cause.
5. Once you get drive to where the tube is saturating (as in more drive does
not yield more output) leave it there for a time. If the plates glow all the
better.
6. Start slowly raising the high voltage a bit at a time, adjusting drive
until you are at where the tube is at rated output (remember this is one of
two, so it will be half the normal output of the amp).
7. If you get to the point where you can get the plates reddish, leave it
there for an hour or so.
8. Repeat for the second tube.
Your mileage may vary. I'm sure others will comment and may have more
elegant methods. If you aren't comfortable doing this I suggest getting
some help. Remember, high voltage kills!! Be careful!!
Chris, AB6QK
ORIGINAL MESSAGE
----------------------------------------------------------------------
Message: 1
Date: Tue, 6 Jun 2017 10:20:47 -0500
From: Joe <nss@mwt.net>
To: Catherine James <catherine.james@att.net>, Amps group
<amps@contesting.com>, Kimberly Elmore <cw_de_n5op@sbcglobal.net>
Subject: Re: [Amps] 3-500Z cool down time
Message-ID: <fdf26300-3f43-cd29-249d-32d95dff9146@mwt.net>
Content-Type: text/plain; charset=utf-8; format=flowed
So this SB-220, that has been sitting since 1993, the tubes are most likely
toast?
Joe WB9SBD
Sig
The Original Rolling Ball Clock
Idle Tyme
Idle-Tyme.com
http://www.idle-tyme.com
On 6/6/2017 10:14 AM, Catherine James wrote:
> Kim,
>
> It's generally recognized that glass tubes have poor shelf life due to
slow leakage. I have heard many reports of this from people I trust.
>
> They will last much longer if the plate gets hot at least a few times
a year so that any leakage can be gettered away. For tubes in regular use
rather than on the shelf, it doesn't seem to be a problem, but it makes it
difficult to stock up with spares. Many amateur users rotate their shelf
stock into the amp at least once a year.
>
> Is the 3-500Z used much outside of ham radio today? If so, who are the
primary users?
>
> 73,
> Cathy
> N5WVR
>
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