[AMRadio] Globe Champion 350 & HQ-170A


Jim Wilhite w5jo at brightok.net
Mon May 14 16:13:24 EDT 2007


I sort of think Leo liked as much power as he could 
advertise out of a small a radio as possible.  The Champ is 
about the size and weight of a DX 100 and put out about 
double the power.  So the AX 9909 fit that pretty well.  Too 
bad it was such a fragile tube.

Going to a 4CX 250B would have required a socket change. 
Like you, I worked with what I had so the sockets stayed the 
same and I used the 8643 rather than the 5894.   I had 
access to a lot of 5894s and a few 8643 since I spent many 
years in the land mobile business.  They were used by 
Motorola in their Micor line.  The only thing I had to 
fabricate was for the 8643 plate pins.  My friend Glen Zook 
suggested getting a 3 ft. piece of aluminum stock 1 inch X 
1/4 inch at the hardware store, cutting  two 1" pieces and 
drilling and tapping the holes for set screws.  Gives a bit 
of heat sink for the plates

I didn't like the fan set up either, mostly because of the 
noise.  I happened to have a small muffin fan that ran from 
110 VAC.  I mounted it on the other side of the shield from 
the tubes and the opening in the muffin fan fit the hole for 
the other.  I don't remember the model number of the fan, 
but it was about 2 inches square and 3/4 inch thick.  I did 
have to remove the shield and drill one hole for a mounting 
screw since the pattern was different.

It works but you have a better margin for tube HV.  I hope 
my holds out for a long time.

Jim/W5JO



>
>
> Kim et al:
>

>
> More importantly, none of the tubes were spec'd for the 
> kind of service used in the 350A although clearly they did 
> work for others. Just about only common tube I found that 
> had published specifications for AM operation at 1000 
> volts on the anode was the 4CX250B, which I had a few of. 
> The interelectrode capacitance and so on are also 
> extremely close. So that's what I did and it's worked ever 
> since, even after I dropped the rig on a dirt floor in a 
> friend's barn when the steps I was carrying it up 
> disintegrated under me :(
>
> It's a simple mod on the A, harder on the others. The fan 
> is removed and the tube socket sits in a tuna can mounted 
> vertically over the fan hole with the flat squirrel fan 
> mounted atop one of the transformers feeding a plastic 
> tube plenum. Electrically the filament has to be dropped 
> by .3 volts and the drive increased since it's a tetrode, 
> but as I recall that's all that's needed. A no-holes mod.
>
> I should write this up but it's been a tough ten years...
>
> 73,
> -Pete
> WB2QLL
> Somers, WI




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