[Drake] minor B-Line problem

[Dennis Monticelli]

I agree with Garey.  Most likely it is normal ageing of the neon lamp;
the trigger voltage drifts high over time.  That is why the lamp in
your power strip first starts to flicker and then eventually goes
dark.  Same mechanism.

An NE2E of the proper size is your best route.  I say this because the
lamp driver transistor, a 2N3877, is only rated for an OFF state
breakdown of  70V.  Resistor R150 is in there to limit the OFF state
voltage to  about 115V.  That is high enough to trigger a healthy neon
yet low enough to allow typical 2N3877's to survive because the neon
lamp limits the breakdown current (it is actually a collector-base
avalanche current) to a very low level.  But considering how far this
little transistor is being pushed as it is, I wouldn't push it any
further, despite what Drake apparently recommended.  If you are
ambitious you could replace the 2N3877 with a higher voltage
transistor, eliminate the breakdown issue altogether, and cut out that
100K (R150) that caps the trigger voltage.

I have small high voltage transistors laying around the bench and it
was still easier for me to just plop in a new NE2E in my R-4B.

Denny AE6C



On 12/26/06, Garey Barrell <k4oah at mindspring.com> wrote:
> Tom -
>
> The problem is most likely the neon bulb behind the dial.  Neon bulbs
> tend to increase their "triggering" voltage with age, especially when
> they are in a "dark" area.
>
> There are a couple of "almost official" fixes.
>
> 1.  Remove R150, the 100k resistor across the switching transistor Q10.
> This is the Drake fix, and is what they did when one came in for
> service.  R150 is located on the small board just behind the front panel
> under the chassis beneath the PTO
>
> 2.  Replace the neon bulb with an NE-2E.  The modern designator for this
> bulb is A9A.  Unfortunately, there doesn't appear to be a standard
> length for this type of bulb.  Some are too long to fit in the small
> aluminum light shade behind the dial.  This can make it difficult to
> order a replacement by mail!  Replacing the bulb can be frustrating, the
> leads are short, and the front panel must be removed to get to the
> wiring.  Three or more hands are a definite advantage!
>
> 73, Garey - K4OAH
> Atlanta
>
> Drake 2-B, 4-B & C-Line Service Supplement CDs
> <www.k4oah.com>
>
>  >
> Tom McDaris wrote:
> > I hope you folks can give me a tip on a B-Line problem.  Set is in fine working order except for the little light on the R-4B that is supposed to come on when you tranceive in the Receiver VFO controlled mode.  The light comes on when you first turn the R-4B on but goes out when you turn the switch to transmitter VFO control (as it should).  Problem is that when you turn the switch back to receiver control the light stays out.  I am talking about the switch on the T4XB.  Do you think the problem is in the switch or elsewhere?  Rig works fine and is clean as a whistle.  Thanks   AB8BW
> >
> >
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