----- Original Message -----
From: "R. Measures" <r@somis.org>
To: "W0OXJ" <rfjones@ris.net>
Cc: <amps@contesting.com>
Sent: Saturday, January 29, 2005 6:33 PM
Subject: Re: [Amps] TL-922 Troubles
>
> On Jan 29, 2005, at 4:33 PM, W0OXJ wrote:
>
> > I have been running a balanced pair of 3-500ZG's for 3 years.Recently
> > the
> > amp made a loud pop and began arcing while at idle.I turned it back on
> > after
> > a period of time and noticed a loud hum and the filament transformaer
> > was
> > getting warm.
>
> A filament got pushed sideways and shorted against the grid cage. Are
> you using the stock vhf suppressors? Did you install a glitch R?
The amp is 100 percent stock,Richard.What is a glitch R?
> > One tube has fresh paint on it and the other had faded paint which
> > seemed
> > strange.The tube with fresh paint does not look used at all.The tube
> > with
> > faded paint had a red plate after 45 seconds of excitation under low
> > drive
> > and a loaded final.I swapped out tubes with a spare Eimac 3-500 and
> > the tube
> > with fresh paint proved to be causing the heavy draw on the filament
> > transformer.I also notice no idle current where I used to have 150 ma.
> >
> > The amp seems normal,it loads but I didn't try to load it fully.The
> > relay
> > seems to operate OK,the 3-500ZG plate stills glows faintly red.
> >
> > In the past I have noticed one tube would turn red after a period of
> > keydown
> > but was not concerned as the amp has delivered 800 watts out for three
> > years
> > .
> >
> > Now I plan on replacing the defective 3-500ZG but would like to know
> > what
> > could be causing the imbalance? and is this the reason for the failed
> > tube.Will a new tube be matched enough to give good service with the
> > existing tube?Why no idle current?
> > Both tubes check out with an ohm meter,no shorts between the three
> > elements.
>
> The tube with the bent filament only shorts when the filament is hot.
> Operating a stock 922 with a grid-fil shorted tube will destroy T2.
> There is an article on the 922 on my Web site.
I'll take a look at your website and certainly consider the suppressors.
> > I can't do any voltage checks until I replace the 3-500ZG and will
> > follow
> > the instructions in the service manual.They mention a bad zener,bad
> > relay
> > and a bad tube as causes for this condition.
>
> The bad tube is the result of an intermittent oscillation c. 120MHz.
> Good luck, Bob.
As always thanks Richard.
> > Any advice or experiences would sure help as I would like to insure a
> > few
> > more years of reliable operation.
> >
> > Many thanks and 73,
> >
> > Bob
> > W0OXJ
> >
> > _______________________________________________
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> > Amps@contesting.com
> > http://lists.contesting.com/mailman/listinfo/amps
> >
> >
>
> Richard L. Measures, AG6K, 805.386.3734. www.somis.org
>
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