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

[measures]

>
>> My guess is that gold-sputtering is caused by caused by UHF.
>
>> >Are you saying that during the sputtering no grid current flows?
>
>> no.  The grid can rectify MF, HF, VHF, UHF.  My guess is UHF because of
>> the typical pattern of missing gold on the grid.
>
>All my 8877 amps have a grid-trip circuit similar to those found in the ARRL
>Handbooks and Bill Orr's Handbooks.
>
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.  

>The voltage drop across the grid meter shunt is sampled through a 10k ohm
>pot that drives a TIP-120 transistor that latches up a relay to open the PTT
>line.
>An 8877 has no business having over 75 ma grid current flowing for any 
>reason.

Only c. 5W?

>If this current level is reached from whatever cause; MF, HF, VHF, UHF, 
>broken
>antenna/feedline, bad T-R relay sequencing, wrong band, wrong antenna....
>(reader can finish the list!) the relay latches when 75ma grid current is 
>reached.
>The same glitch diodes that protect the grid meter protect the grid-trip 
>circuit.
>This is faster and happens much earlier in a fault condition than fuses or 
>resistors.
>
>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?  

later, Phil, K5PC
>
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-  Rich..., 805.386.3734, www.vcnet.com/measures.  
end


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