[R-390] 3TF7 replacement

[Tisha Hayes]

I have one of the plug-in sold state replacements made by Dr Kurt Schmid
(ebay: sigmapert) for the 3FT7. Here are some things to consider when
looking at a solid-state current regulator;

If you use a linear regulator the device must be capable of dissipating
about 8 watts of heat due to voltage drop. This requires some forethought
when coming up with a heat sink.

The specifications for the regulator are built right in to the model number
of the tube; 3FT7 means 300 mA, 7 V drop.

Ballast tube regulation is not all that good when compared to a solid-state
device. Not that it takes much regulation for the PTO/BFO to remain
frequency-stable.

NIB 3FT7's can cost $30-$60 USD.

You can buy a good solid state regulator for about the same and never have
to worry about it again.

A good article on the 3FT7 ballast can be found at;

http://www.radiomuseum.org/forum/ballast_tubes_in_filament_regulation_of_vfo_tubes.html

And on the particular regulator I have;

http://schmid-mainz.de/Flyer.pdf

*Ms. Tisha Hayes, AA4HA*
*"*There are many who live in the mountains and behave as if they were in **the
town; they are wasting their time.*
* It is possible to be a solitary in one's mind while living in a crowd;
and it is possible for those who are **solitary to live in the crowd of
their own thoughts.*"*
**-Amma Syncletica of Alexandria**