|JUMA PA100 Recommended Modifications 2013-05-14
The following modifications are recommended for JUMA PA100 especially in heavy use.
1. The capacitors in the RF low-pass filters (Applies only Main Board Rev A) which are between the two toroidal inductors must handle lot of RF current. It is recommended to replace the middle capacitor with two capacitors in parallel. This is especially important with C27 for 21MHz...28MHz bands. Suitable capacitor type is a ceramic C0G with a voltage rating of 100VDC or higher. Silver mica type capacitors can also be used. Remove the original capacitor and solder one capacitor on top and a second to the bottom layer of the board.
- C12 3300pF => 2 x 1500pF in parallel
- C15 2200pF => 2 x 1000pF in parallel
- C18 1000pF => 2 x 470pF in parallel
- C21 680pF => 2 x 330pF in parallel
- C24 330pF => 2 x 150pF in parallel
- C27 220pF => 2 x 100pF in parallel (this is the most essential LPF modification)
2. SWR bridge transformer T2 (Applies only Main Board Rev A) has little too low inductance and it can heat up especially in lower bands 1.8MHz and 3.5MHz. It is recommended to change the toroidal core from Amidon FT-37-61 ferrite toroidal core to bigger Amidon FT-50-61 core. The winding turns are the same as original pa100-toroidal-cores.pdf
3. Fan speed control circuit in Digital Control Module. Short circuit R1 (47R) to zero ohms. This will give full fan speed when needed. This modification applies only for model PA100-D.
Refer to the corresponding schematics, part lists and layout drawings in PA100 technical page.