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President Jackson very low output power
Posted: Sunday 16th Dec 2007, 4:24
by 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.
Re: President Jackson very low output power
Posted: Sunday 16th Dec 2007, 11:04
by 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.
Posted: Wednesday 19th Dec 2007, 5:00
by 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.
Re: President Jackson very low output power.
Posted: Wednesday 19th Dec 2007, 8:17
by 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.
Posted: Thursday 20th Dec 2007, 3:00
by 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.