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

Patrick Jankowiak recycler at swbell.net
Wed Jan 5 02:51:18 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.

> From: Don Moore R Moore <wa5ffk at juno.com>
> Subject: [AMRadio] Matching a 100 watt PA am to drive 833'S
> To: amradio at mailman.qth.net
> Cc: amradio at mailman.qth.net
> Message-ID: <20050103.231108.-433693.0.wa5ffk at juno.com>
> Content-Type: text/plain; charset=us-ascii
> I have a older BC 1F series gates transmitter.  I would like to do away
> with the 845 driver tubes and drive the 833's with a 100 watt PA amp. 
> Does anybody have any Ideas what I would need to match the amp to the
> driver transformer of the 833's.
> Don Moore

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