President Jackson very low output power

[James Unit 198]

President Jackson
PCB #PB042 AC
PLL MC145106
PA Final MFR455.
This model has Automatic Squelch ASC.

The output power is very low at 3 watts on AM and FM and about 7 watts on sideband. i have try adjust the power on AM with vr11 but this only turns the power down and max is 3 watts i have tested the MRF455 final and the driver 2SC2166 and are ok. i am stuck as to what to test next. Can anyone help.

James.

[Rick]

Check the bias on TR503 and TR502 you may find R241 o/c this is not uncommon. If it's o/c then change the driver (TR503) and C195. Let us know how you get on.

[James Unit 198]

you was right r241 was o/c and driver transistor has a leak from emitter to base. replaced r241 tr503 c195 but the power is still low at 6 watts am and 13 watts on ssb i have noted that the driver is getting very hot and i can not touch it as it is so hot. do you know what i need to do next?

James.

[Rick]

Try replacing C192 (390p) use a good quality cap mica is the best, it maybe best to replace C195 with mica type. I know the radio original caps were disc ceramic but to make the PA more reliable use mica type.

Check the bias, and if necessary re-set the driver for 50ma and the final for 120ma on mode SSB with the mic gain at minimum, TP9 and TP8 for Driver and TP9 and TP7 for Final.

[James Unit 198]

You certainly know your onions mate you was spot on. replace the 2 caps you told me to with mica ones put them on the copper side as the only ones i could get was 350 volts silver mica. set power to 10 watts on am and fm and 20 watts on ssb.

Thanks for all your help.

Happy Xmas.

James.