Just to keep the record straight...I did not suggest replacing only the one
that went bad, but also its mate in the p-p amplifier as well, being mindful
that they should be matched and in the same beta group as the other six.
I am only relating what has worked for me in the past, and I consider it
folly to replace all eight transistors ( 2 in each of the 4 amplifiers) when
only two of them need to be replaced (the bad one and its mate).
Of course, if you would like to replace them all, that's certainly all right
with me.
73
Phil
----- Original Message -----
From: "Ken Brown" <ken.d.brown@verizon.net>
To: <ve1adh@accesswave.ca>; "Discussion of Ten-Tec Equipment"
<tentec@contesting.com>
Sent: Tuesday, November 15, 2005 11:25 PM
Subject: Re: [TenTec] repair of Herc II amp RE Phil (k4dpk)
> I have repaired dozens of GE Mastr II 100 Watt UHF PAs, and a few VHF
> ones too (the VHF ones have reverse power protection and do not fail as
> often). I have opened up the PA transistors (not recomended as you and
> inadvertantly inhale Berilium Oxide dust which is toxic) and looked at
> them under a magnifying glass. Every RF PA transistor I have looked at
> has multiple emitter wires and multiple collector wires connected to the
> silicon chip. It appears that they are actually several transistors on
> one chip, connected in parallel to the outside container package leads,
> or maybe just multiple parallel wires to a single transistor in order to
> reduce lead inductance. Often transistors that still work, but not up to
> par, have some of the little wires fused. My experience has been that
> when one transistor in a PA goes bad (or just partially bad) the other
> transisitors get stressed and you usually see toasty resistors in the
> Wilkinson power combiner. If you only replace the really bad
> transistors, the other ones go bad very soon thereafter. Replacing all
> of them at once saves enough labor that the parts cost is justified.
> Perhaps this is not the case with HF PAs.
>
> DE N6KB
>
> >These transistors have a
> >multi-emitter arrangement that enhances bandwidth. I
> >believe that if one or more of these multi-emitter
> >paths is open the transistor will still work but on
> >the mid or lower HF bands only. I don't think you can
> >tell the difference with ohmmeter checks.
> >
> >
> >
>
>
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>
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