[Boatanchors] Thoughts on Reviving the Heathkit DX-100

[w5jo at brightok.net]

It has been a very long time since I have read how tube manufacturers 
specified the plate voltages for tubes, but I do remember that altitude has 
something to do with it  along with what type of envelope, the insulating 
material that holds the elements and more.

There is a lot of mis-information roaming around about that subject and 
other vacuum tube properties, so if you are concerned about voltages then I 
suggest some looking on the subject.  A couple of good books about tubes, 
applications and operation are the tube books printed by RCA.  While they do 
not cover the way the HV specifications are determined they do talk about 
what design considerations are taken into account when manufacturing tubes. 
There are two books, the Receiving Tube book and the Transmitting Tube book.

The books state the the AC input design voltage for the equipment is 117 
volts and most all mains adhere to  +/- 10% and that is 12 volts added to 
117 volts or  subtracted from it.  If your mains voltages run over 127-8 
volts then look at bucking or reducing the voltage.  As Glen says, the 
filament voltage is the import one to be sure of.

Jim
W5JO


-----Original Message----- 


Starting just after World War II, the 1625 was definitely run at higher 
plate voltages than the ratings.  Like the 6146, the 1625 can handle 
considerably more plate voltage than the 750-volt specifications.

It has been my experience that the DX-100 is not a "weak sister" and that it 
can take a lot of abuse.

The Hallicrafters HT-32- series, the HT-37, and the Collins 32V- series all 
have a serious power transformer problem with the rectifier filament 
windings tend to short out within the transformer.  Those transmitters 
really need the high voltage rectifiers changed to solid-state and the 
rectifier filament windings completely disconnected or used as "bucking" 
windings to reduce the primary voltage on the transformer.  But, such is not 
the case with the DX-100 or with the TX-1 Apache which uses the same power 
transformers.
Glen, K9STH

Website: http://k9sth.net