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RE: [linrad] RX2500

Hi Jim and all,

> I am building the power supplies needed in hopes of having an
> RX2500 for myself.
> Is there any danger of component damage if one of the supplies
> fails in some way? Either one or both could go to some combination
> of 0 volts or +24 volts, so I want to make the power supply failsafe, but
> only if need be.
The first component to fail on overvoltage will probably be the 470 
microfarad capacitor which is rated 25V. 

If you feed plus and minus 24 V to the unit for a long time it will
become much warmer than normal. 

The RX10700 and RX70 units will fail within a few minutes if you operate
the board outside it's box at much larger voltages than +/- 15V due to
inadequate cooling of the IF amplifiers.

At some level, probably around +40V the 7812 and/or 7912 will fail 
immediately. The 470 microfarad capacitors may open and disconnect 
themselves without breaking the fuse. I have not put overvoltage
to units until they fail so I do not really know what will happen.

For my own rig I will use an unregulated supply. Three transformers
from the three phases and full wave rectifiers. The thing will run 
continously and something with very high reliability and high efficiency
will be fine. An unregulated supply will affect the frequency stability,
mainly because the temperature will change with the power put into the 
boxes, but also because of the limited regulation of the 7812 and 7905
that supply DC to the LO transistors. I do not plan to put my boxed
in a well stabilized temperature anyway so it does not matter. If I ever
need better stability I will add phase-locking of the oscillators to
some frequency standard.


Leif / SM5BSZ