Kenwood Tl-922 Repair And Modifications With 40 Meter Output Test. 3-500Z Tubes

[@g0fvt]

My TL922 seemed to have a little more gain with grounded grids... not the best cooled amplifier of all time but elegant looking and I don't rag mine... you mention "self bias" presumably you are talking about the cut-off bias and the usual mod?

[@amprepairguy]

Self bias as in filament center tap / cathode return lifted with a 100k resistor to put tubes into cutoff and biased on by shorting the 100k resistor Stock setup is called forced bias. They rectified a winding on the filament t eta ma former which they fed into the cathode to put the tubes into cutoff. This winding also powers the two relay coils. If ever had a grid to filament short you would most likely damage this winding and then need a new filament transformer. Heathkit had the sb220 bias setup the same way. Grounding grids along with other mods get more stability . And as you said more gain. Stability issues are often most evident on the higher bands and some try different parasitic designs to correct. The mods I implement protect valuable components like the tubes , band switch , plate current meter , air variable capacitors for the output network , filament etc. Once implemented it is a rock solid pa. No issues with the cooling when run within its output specs. Great amp after all mods have been done. Would take one over any of the Ameritron amps any day