SB-220 Power Output Decline

[W8JITom at aol.com]

In a message dated 97-02-11 12:45:36 EST, you write:

>
>I'm looking for information/advice/opinions to help me troubleshoot a SB-220

>amp.  It's output power is declining.  When I first put it into service in
>late 
>November, 1996, it output a kW on 80-15.  Output on 10 was low, around 300
>watts 
>max.  It served me well in the CQWW CW.  Ocassionally, the amp will emit a
>loud 
>POP! noise when turning on.  This POP! is an exception rather than a rule,
>and 
>it has happened with the tune/cw - ssb switch in either position.  History
of
>
>the amp is that it was built new in 1974, and has been in storage from 1985
>to 
>November, 1996.
>
>

The worse thing in the world is a long storage period for tubes like
3-500Z's. The seals slowly leak, and the tube gasses up. That can cause the
pop AND low emission.

The 500Z's getter (remove gas) via the gray coating on the anode. The
gettering agent is activated when the anode is heated to the point of turning
red. There is little hope the gettering material will absorb all the gas,
since the tubes have sat so long. The best try would be to remove the bias
(if the arcing hasn't already done so) or bias the cathode negative and idle
the tubes at 250 watts or so dissipation for several hours at low anode
voltage.

Most likely, you are sunk.  By they way, the change in power with frequency
makes no sense unless perhaps low emission has affected the input SWR. The
system is always more critical on the ten meter end. 

There could be another cause of the popping, and that would be an
electrolytic failure. Electrolytics are also subject to deterioration when a
PA sits dead for a long period of time.

73 Tom

>From bernie.mcclenny at mail.wdn.com (Bernie McClenny, W3UR)  Wed Feb 12 00:40:34 1997
From: bernie.mcclenny at mail.wdn.com (Bernie McClenny, W3UR) (Bernie McClenny, W3UR)
Date: Tue, 11 Feb 1997 16:40:34 -0800
Subject: Changing the date of the WPX CW contest
References: <373449 at mail.wdn.com>
Message-ID: <33011182.3DB0 at mail.wdn.com>

syam at Glue.umd.edu wrote:
> 
> On Mon, 10 Feb 1997, David L. Thompson wrote:
> 
> > Gang,
> >
> > Its nice to discuss changing the date of the CW WPX Contest, but unless you
> > get N8BJQ's ear
> > it will never happen.    CQ has a separate Director for each of the major
> > contests.   The Director must first be sold on the idea.   The Director has
> > considerable lattitude on internal changes, but requires CQ staff approval
> > on changing a "traditional" date.   This date is set for many reasons, but
> > the most important for a fairly new contest such as the CW WPX is the
> > current contest calendar.
> 
> Since the WPX is primarily a DX contest, it would also be interesting to
> see what contest now occupies the weekend being proposed as the new
> weekend for the WPX.  The sponsors of whatever contest it may be may not
> take kindly to usurpation of their long-held weekend in a gratuitous
> fashion by the WPX.  Need the reflector denizens be reminded once again
> that there are other countries in the world besides the USA?
> 
>                                          Very 73,
> 
>                                        Fred Laun, K3ZO

Fred has a good point.  I know many more US stations will be able to 
participate is this what the other countries want?  Will this interfer w/ any 
other Amateur Radio activities?  I think that N8BJQ should collect the data. 
 What say Steve?  de Bernie

-- 
Bernie McClenny W3UR (ex WR3E, WB3JRU)