WHY LOW GRID CURRENT ON 160 ONLY?..

[ve6pg]

..HI FROM TIM..MY VIKING 2 HAS TONS OF RF OUT,AND GRID CURRENT ON ALL BANDS,EXCEPT 160...BEST I CAN DO ON 160 IS ABT 4 MILS,AND GET ABT 75 WATTS OUTPUT...PLATE CURRENT IS BEST AT 200MILS..EVEN A DUMMY LOAD,NO DIFFERENCE ON THE OUT POOT....IDEAS?...SK..

[W3SLK]

Tim, I don't have the schematic in front of me but I would check the driver section of the rig. Sounds like a component changed value that isn't too significant at higher freq.

[Jim, W5JO]

Tim, are meter reading M1 and M2 OK?

[Warren]

Tim,
   I had a similar problem with a DX-100. Turned out to be the coil in between the driver output circuit and the PA grid. The DX-100 switches in extra coils as you go to  lower  frequency bands. The 160 coil had shorted turns and the grid drive was low. It can be tricky to diagnose since the coil will still read good on an ohmmeter.
73 & GL Warren K2ORS/WD2XGJ

[W2JBL]

replace the screen resistors in the oscillator and first multiplier stages (they tend to open up), and swap the 6AH6 to a 6AK6. you should have more than enough drive on all bands after that. same for the 122 VFO- replace all the resistors. they don't age well.

[WA1GFZ]

Good thought Chris. I did the VFO but never the osc / driver screen resistors.
My V2 has the same problem on 160. Changing tubes did nothing to help.
I have not looked at the voltages since '83. when i went PDM might be time to check again. BTW swapped out the modulators for the first time amd found no change so put the old 6DQ5 back in.
gfz