[AMRadio] Matching a 100 watt PA am to drive 833'S


Donald Chester k4kyv at hotmail.com
Wed Jan 5 18:48:43 EST 2005


>I'll take a very wild stab at it. From the RCA TT-4 handbook, the 833's at 
>3000VDC require 400V peak G-G volts, that is 242 V RMS. The drive is 20W. 
>That makes the current 82 mA. That makes the impedance 2950 ohms G-G.
>
>If you have an old output transformer such as a 6K CT to 0-4-8-16 ohm type, 
>and were to connect the transformer's 16 ohm winding to the 8 ohm winding 
>on the power amp, then the secondary would look like 3000 ohms, close 
>enough.
>
>You could also do a chinsel-cheeze method and use a dual-primary power 
>transformer (120V each primary) set up for 240VCT, and with a secondary 
>voltage of 12VAC. Use one with at least 5 amps rating on the 12v winding. 
>Hook the 12VAC winding to the power amp's 8 ohm output. The series'd two 
>120V windings of the power transformer (240VCT) now looks like 3200 ohms, 
>close enough. You might be surprised how good a power transformer can sound 
>when operated far below its ratings.

I think it would be a terrible mistake to mutilate a high quality 
transmitter by going from a design as superbly engineered as the BC-1F, and 
converting it to something as jury-rigged as using a power transformer for a 
driver transformer, or one output transformer feeding a second reverse 
connected output transformer to feed the grids.

Don K4KYV





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