[TenTec] repair of Herc II amp RE Phil (k4dpk)

[David McClafferty]

I have seen RF transistors that check OK for
continuity and will even make full power on 20 meters,
but they drop off on the higher bands and sometimes on
the lower bands. 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. I may be way
out in left field with my theory of how this happens,
but I have replaced transistors in several rigs that
had low output on 10 and somtimes 80 and the problem
was fixed.

Dave, VE1ADH

--- Sam Bridges <radiobridge at InfoAve.Net> wrote:

> Hello Phil:
>     I wondered about replacing all eight trans
> myself, but Gary at TT says that is the only safe
> way. I gather the reason is that (I am told) the
> trans must be matched in current drain or trouble
> will results. Secondly, it appears that RF trans in
> or out of circuit can appear to test good when in 
> fact they will not produce full output. This seems
> to be the result of the physical make up of the
> trans.,viz. part of it will be working but the rest
> will not. As a result the trans will not fail a
> continuity test but be bad. I am new to RF Trans so
> I could be wrong.
>     Anyone know what the resistance between the
> collector and the base should be of a MRF454 out of
> circuit?
>     Tnx de KJ4ZM Sam
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