[AMRadio] Johnson Valiant Audio Driver Xfmr - Wake Up Call


Jim Wilhite w5jo at brightok.net
Mon Oct 22 20:35:37 EDT 2007


The stock Valiant used 600 Volts for the HV section.  According to the 
book CCS is 480 and ICAS is 600 volts for Class C modulated RF amp. 
Given the duty cycle of ham transmitters using 600 volts is safe.  They 
actually will stand more than that.  The Apache/DX 100 used about 750 
volts loaded, which works just fine and the two transmitters had similar 
components.  When in Standby the Heath voltage rose to about 800.

The Valiant had three 6146s and gave 100+ watts, the DX 100 had two and 
gave the same power level.  Part of the HV increase you see is that your 
primary voltage is probably near 125 volts, whereas when the Valiant was 
built, the primary voltage was near 117-120 which accounts for some of 
the higher voltage.  If you are uncomfortable then put a variac on the 
primary and lower the voltage to the input.

The Viking 2 is almost the same transmitter as the Valiant with an 
internal VFO and different cabinet.  If everything is working right, the 
Viking 2 will do just fine, I have used them in the past with the 
voltages you mention.

Jim/W5JO



> How much plate voltage will the stock VKII tank components handle?  I
> have a VKII chassis in need of a serious rebuild and have been
> considering external MOD and a different final tube/s.  Without the 
> Mod
> circuit the available current can run upwards of 400 ma. and solid 
> state
> rectifiers put the Plate V around 800V or better without the Mod load.
>
> Bill KB3DKS/1



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