Hi all, First off hello everyone. A little about me. I lurk but never post I am a local radio tech here in Rochester NY. I have been working on radios and amps for 35 years. My history is associate in electronics technology, work at Xerox as electronics and mechanical technician, have worked at Harris communications as a tech., and MKS instruments as a tech on all aspects from power supply up to combiners but mainly on super hi power RF amp boards used for plasma cutting and MRI machines. The HR2510 is a new radio for me and I have crammed so much in of info its ridiculous. Kudos go the my local neighbor DOC at Doc;s electronics Buffalo for pointing the way on a couple hard spots and Rogerbird for pointing out the troubled capacitor areas. I replaced all the 10v caps to 25v or better on the main board, and the usual power supply caps. Upgraded power wire from connector to board with 12g. Pre driver mod Q134 removing the network from the emitter. Modulation improvement a 1k resistor to the emitter of Q114. Added 680pf cap parallel to C127 a 330pf which is now become a 220pf, also a 220pf cap paralleled to C126 an 820pf now becoming ruffly 170pf, for more driver to final drive. Any help on these caps also appreciated. Better ground jumper for the 2166 driver. Replace antenna connector wire with a 18g Teflon wire from board to SO-239. Replaced VR112 pot with a ceramic pot of same 100 ohms. The adjusting is very touchy and I wish I could change it for another value that would act like a ten turn clarifier pot for better adjustment. Maybe then the following would happen so drastically. . This is a trouble area for me as the mA's are not steady at 80ma i set it to 75ma and the more I stay keyed down the ma bias value increases with time up to high 90's even 100 or more. . Not using the paralleled double caps on the final on foil side or a biasing diode. I will however add a .1uf 100V Mylar cap and 100 ohm 3 watt resistor for a feedback circuit on mrf455 from collector to base. L123 next to ring core reduced from 7.5T to 4.5Turns. ALL limiters AM, SSB replaced and intact. They were gone when I got this radio. The two receive diodes D111-112 with schottkys 1N5711's. Replaced various caps for HiFi receive and TX. I am looking for the directions found in an old post below. Only to verify pf PA cap values to my already started MRF455 mod that works great but still needs help. I have to upgrade the caps for the PA final output and I want to verify if I replace with 500v silver mica's of same pf or am I changing values here. Anyone done these PA caps and what values did you use if you did? Below is a copy of that post AND what was also suggested by JUSTme, and his suggestions rock.. Any help is greatly appreciated. As always I want to do it right. Thanks in advance! Joe N2WNY email@example.com The old Post\\\\\\\\\\\\\\\\\\\\\\\\\\\ here is a real good power modification for the hr-2510 Materials: 1 47uF to 100uF 25V capacitor. In this spot C119 I used a .47uf 160V suggested by DOCbut not sure why others are using a 100uf 35v here 1 68 ohms resistor 1/2w DONE 6 silver mica caps (values shows in pictures)(they are really needed)C112-117 I have no pic's Any others I should change maybe near the SSB ALC circuit 1 SD1446 Pill (more cheap than mrf455) DONE with MRF455 double black dot 1 small piece of wire DONE using 18 gauge Teflon wire from TP4 to incoming power wire Adjust am power to no more than 15 W dead carrier. Adjusted to 10W carrier when the radio is finally warmed up or else its 5W. working on that. looking at issue might be one or more of the 3 small red diodes. Download instructions here. Broken link http://rapidshare.com/files/125848670/HR2510-_____PowerMod__.zip.html Justme Posted a great response: First, this is just an ordinary improvement which can be found on the net, the only difference is you indeed replace the C's in the PA stage for larger power handling ones. no mention of value changes just higher power handling ones Secondly, i use thee MRF455 and get 65 watts easy, grounding the emitters is crucial, removing the - lead from where it is soldered to the PCB to the point where the emitter leads are of the new transistor will up the gain. DONE Secondly, you still let the DC go through the first ring-core which degrades the handling capability of said ringcore, disconnect the + through the ring-core, and bring the + directly from the + input wire through an decent rf choke and decoupling to the collector. Pulling 70 watts SSB and 20 watts carrier in AM and 75 modulated here. Then use screening to prevent the hf radiating into the rest of the radio. What type of screening? Copper tape formed around a paper cover over the ring cores only or the whole output section? More power is fine, but how about reception? Replace the first stage transistor with an decent transistor, i use thee European BFY90, you will find an replacement over there, the BFY90 is an low noise fist stage pre amp transistor with an cutoff frequency of 1300 MHz. Working on ordering this to replace Q103 but not sure if I need to also replace Q105 being thay are the same, even though it says first stage transistor. Then put in an xtal filter of 10.695 MHz in the MF replace the first C of 3 pF where you see 3 cans which serve as rude band-pass filter. I have a 10.695 MHz plain old crystal, the short oval case ones sold these days for cobra radio's, and its saying to put a crystal filter not a regular crystal in place of the 3pf cap found at C13. with this regular crystal suffice? This will prevent bleed through, sharpen the bandwidth of your MF, and improve reception.