[Hallicrafters] SX-117/HT-44

[Langston, Mike]

Hello everyone and Happy New Year,

 

I'm still struggling with output on my HT-44. Fortunately, there are so many combinations of VFO's and Heterodyne oscillators, it has helped me to correct a few problems already. The schematic for the cathode follower section of V-15 in the HT-44 showed R106 to be 470K but my rig had a 1Meg. I changed it out for the proper value and the HT-44 Het. Osc. now provides slightly more output on the high bands than the SX-117. I definitely have a problem with low output from the HT-44 VFO. Using either Het. Osc., the power output is about ½ using the HT-44 VFO vs. the SX-117 VFO. Swapping the 6EA8's from one to the other makes no difference so it's not the tube. I've peaked L2 in the 44 (made no difference as it was about right) and peaked L18 in the 117 (helped the output using the 117 VFO but just increased the difference from the 44 VFO).

 

So, that's my first problem, low VFO output on the HT-44.

 

Next, there seems to be a gain problem at the higher frequencies somewhere between the first mixer and the driver stage. Using the SX-117 VFO, the outputs are approximately 135 W/80, 135W/40, 75W/20, 35W/15 and 20W/10. Even on 40 and 80, it takes full rf level control to reach those outputs and the finals never reach saturation. The finals are NOS, matched and properly neutralized. Another symptom, on 80 and 40, when I run the rf level control up, the output power goes to 135W, then gradually sags back to about 115-120W. This power sag is evident on the higher bands but not as dramatic because I can't get enough output in the first place.

 

I've adjusted the driver and final plate mixer coils. My next step is to swap out the 1st mixer, IF amp, 2nd mixer and Driver tubes to see if that helps any. It seems to me that I should be able to drive the finals to saturation with the rf level control, even if the output is less than 100W.

 

The final bias is right, the rig has been re-capped and I've checked all the resistor values in the stages affecting gain. I also checked tube pin voltages against the manual. The only voltage that troubles me is pin 2 of V8 (2nd mixer), where the manual states 0.5 to 1.5v (MOX depending on band position) and -130v (standby). I actually measured -0.9 to -1.41v (MOX) and -107v (standby). Also, V7 (IF amp) pin 7 reads 115/132v (s/b 125/140v), and pins 2 and 9 read 0.5v (s/b 0.0v).

 

Any ideas, suggestions etc. would be greatly appreciated.

 

Tnx es 73,

Mike Langston

KL7CD

Dallas - Ft. Worth