[Amps] 8122 x 12

[G3rzp at aol.com]

In a message dated 30/12/2004 07:57:33 GMT Standard Time,  
avilaseca at bluewin.ch writes:

>  I've got some papers from an IEE Conference on HF back in 63, where  they
> were described. There'a also a paper from STC about a 60kW tx:  

Could you please make some info available?



I can photocopy and mail next week - I could try getting the XYL to use her  
scanner if she has time before she goes off on her next business trip.
 
Personally, I'd just use the distributed amplifer as a source of parts. Use  
4 4CX250B's for 1kW out, and you'll get a relatively clean 1kW. 4CX250s  
aren't the most linear of tubes - bear in mind the basic design is 1946, and  they 
weren't looking for linearity much then -  but put some negative  feedback on 
it and you'll improve the linearity - I assume you're driving  from the usual 
transceiver power level, so you've plenty of power available in  passive grid. 
Use a shunt regulated screen supply, too. Easiest way to do NFB is  something 
like a 10ohm 2 watt metal film resistor in the common cathode lead to  the 4 
tubes, shunted by an RFC of around 10 or 20 microhenries, wound on a bit  of 
ferrite - you want an impedance of greater than 100 ohms over the operating  
range. You can often liberate suitable chokes from old switching power  supplies.
 
73
 
Peter G3RZP
 
10 4CX250B's for a kW is still a lot of electricity for the blower, heaters  
etc. And nobody describes distributed amplifiers as power efficient for narrow 
 band work.