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[AMPS] Blown TL922A... What to do?

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Subject: [AMPS] Blown TL922A... What to do?
From: philk5pc@tyler.net (Phil Clements)
Date: Thu, 14 Sep 2000 05:47:29 -0500
> I understand that the AL-1500 has a grid-trip circuit.  The 8877 (s/n
> HSZ501)I tested this morning had gold-sputtering.  It was removed from an
> AL-1500.

Alas, the grid-trip circuit in the AL-1500 limits at a whopping 175ma Ig, and
is not adjustable.

> >An 8877 has no business having over 75 ma grid current flowing for any
> >reason.
>
> Only c. 5W?

At 2250 watts output, an 8877 draws less than 65 ma grid current.
75 ma limiting is plenty of headroom. A cap sits in the base circuit
of the TIP120 to prevent nuisence trips.

> >8877's are $700 + per pop (pun intended) now from RF Parts. The above is
> >really
> >cheap insurance. Works good, lasts a long time.
> >
> Ever ran an 8877 with no suppressor whatsoever?

I have not personally, but if you look at old Orr and ARRL Handbooks,
you will see several 8877 projects sans the Supp.

(((73)))
Phil, K5PC




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