[Boatanchors] HT-32

[rls19]

It should be noted that insulating a transformer or choke from the chassis can be dangerous to anyone subsequently working on the unit because the device becomes a shock hazard if there is a short to the frame.

73,
Bob AD3K

> On May 25, 2019, at 5:22 PM, Rob Atkinson <ranchorobbo at gmail.com> wrote:
> 
> Thermistors can work well under the right circumstances but two
> conditions apply:  1.  They are positioned so they can dissipate heat
> safely because they run hot.  2.  They have time to cool down before
> being used again.  In other words, if an AM rig is switched in and out
> of transmit by switching the primary of the PA plate supply
> transformer, then the thermistor in series with the transformer
> primary line needs some off-air time to cool down before being
> energized again.  The protection they offer goes away if they stay hot
> as in for example a number of brief closely spaced transmissions.  If
> the rig is operated in a net or roundtable where there are 15 or more
> minutes off-air then they're fine.
> 
> I speculate that if the rig has a 10H choke input filter and 10 or
> less mfd capacitor following the choke, then in-rush may not be so bad
> compared to a 30 or 40 mfd capacitor filter.  Then the transformer
> failure mode of concern may be a short from the secondary winding to
> the core and that can be guarded against by insulating the transformer
> from the chassis.
> 
> 73
> Rob
> K5UJ
> 
>> I have used the CL-60 inrush limiter (and others) in several Johnson 500 transmitter rebuilds and the limiters work great.
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