[Amps] 2 x 4-250A Amp

[Ian White GM3SEK]

Mark Kachel Wrote:
>>I need to build a power supply and from what I can see,
>>using the tetrode
>>board from IFWTech / G3SEK will make life a lot easier. I
>>was planning on
>>getting the screen bias voltage for the tetrode board by
>>taping across the
>>lower caps in the power supply. Not much current is drawn so
>>I don't see
>>that this will cause a problem. What do you think?>>
>>

W8JI replied:
>I think it is a very poor idea unless the amp has some very
>stout equalizing resistors. In the first place it would be
>very difficult to regulate the screen, and the screen needs
>regulated. It also needs a shunt regulator, or a series
>regulator with a heavy bleeder.  It also needs current
>limited.
>
>Personally I'd never even consider tapping down on a series
>string of electrolytics. It's just asking for problems.

Sorry to have missed the start of this thread (broken phone line).

When you look in more detail at the current requirements for a screen 
regulator, you'll find they are much higher than the current you would 
normally run through the equalizing resistors for a string of 
electrolytics. The downloadable user manual for the Tetrode Boards 
explains this in detail, and the same calculations apply to any kind of 
shunt regulator.

A series regulator would involve similar calculations, and would require 
similar currents.

My board would stabilize the voltage OK, but it requires separate 
transformer windings for the screen and control grids. I'm afraid these 
are just part of the added complexities when using tetrodes.



-- 
73 from Ian GM3SEK
www.ifwtech.co.uk/g3sek/boards