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Help with HR2510 Final PA mica caps replacement and more.

Discussion in 'CB Radio Modifications' started by Xracerx13, Oct 8, 2017.

  1. Xracerx13

    Xracerx13
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    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 alcohol@rochester.rr.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.
     
    #1 Xracerx13, Oct 8, 2017
    Last edited: Oct 8, 2017

  2. bob85

    bob85
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    What do you mean not using a biasing diode?

    its normal for idle current to increase with temperature because bipolar transistors conduct harder the hotter they get,

    the mv1y diodes are there to reduce bias voltage as the transistor gets hotter to keep idle current more stable & stop thermal runaway,
    idle current will be up and down like a yoyo if you don't have the tracking diode,
    its a good idea to fully warm the rig up before setting idle current even when you do have a tracking diode,

    a 2 wire 10.695 crystal is not a filter,
    a filter has 3 wires with a center ground connection like 2 crystals in series,
    i use 15kc 10.695 filters from old cordless phones because they are less critical of incorrect terminating impedance & don't make the RX too narrow,

    2510's 2830's & early lincolns have a place on the board for an extra ssb filter like the jackson uses,
    if you look at the schematic around q104 you will see hand written additions to the schematic where they left out the filter & added a few components to bypass it,
    6kc or 7kc filters work ok in that position once you remove the bypass additions,

    later versions don't have the place for the extra filter.
     
  3. Xracerx13

    Xracerx13
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    Thanks for the reply,
    I am not using a biasing diode yet because I was told by Doc in Buffalo it wasn't needed. I new it needed it. Rogerbird did tell me to use one, btw..He suggested I try a 1n4003 and mount it so it rests against the ceramic with heat transfer compound

    As far as the crystal filter goes I couldn't edit my post to rewrite that I do in fact have an actual crystal filter that I made from CBC plans with two 10.695 crystals. Except CBC says to install at C15 and JUSTME says to install it at C13.
    Yes I have seen the 3 legged ones,

    I am not seeing the hand written stuff on any of the schematics I have for the 2510, and I believe I have a later version radio anyways..
     
  4. bob85

    bob85
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    You need the diode if you want some thermal runaway protection & more stable idle current,
    a 1n4003 will work ok, you can file a flat on the diode to get better thermal contact but its not critical to it working,

    either place will work for the filter, not sure if one is better than the other, both may effect the operation of the noise blanker,

    i have not seen a later 2510, the later version we got in the uk were Lincolns with the revised mainboard & crystal filter on the FM board,
    its 20 years or more since i was putting filters in them.
     
  5. Xracerx13

    Xracerx13
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    Good morning,
    I know its better to have the diode up against the transistor body so this is a dumb question. Why cant I just re-use the original and mount it to the heatsink direct to original place where the 477 used to be? In this spot it would not be directly behind the transistor.

    Picture below is not my radio, its something I found on the net for diode placement purpose. In this pic it shows the diode with the negative cathode coming down to the left. But wouldn't it be better if the positive anode is attached to the other emitter down on the board rather than the heatsink one. Also the board layout pic I have shows the diode complete opposite of which I believe is the wrong way and an error on the PCB layout. My MV1YH's are sealed in black epoxy so I cant see the diode but there is a white dot on the left, I take it for the positive side.
    Could you confirm this for me, please?.

    455protectiondiodeLarge.JPG hr2510_pb111ab_main_pcb.gif
     
    #5 Xracerx13, Oct 10, 2017
    Last edited: Oct 10, 2017
  6. bob85

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    i can't see which way the diode in the pic is connected,

    the cathode goes to ground, anode connects to the bias supply so that it shunts the bias supply to ground & only allows about .6v on the base of the transistor,
    if the diode is the wrong direction it won't do anything,

    you can measure the mv1y with a multimeter on diode test & compare it to a diode that has a clearly marked cathode to confirm which way round it goes,

    the diode or mv1y can be mounted on the heatsink as close as possible to the transistor or mounted on the transistor cap as shown in the pic,
    mounting it further away from the transistor slows response time due to thermal lag,
    for best tracking you want the diode as close as possible to the source of heat,

    if it was me doing the 455 final mod i would etch a small board like the factory 455 mod to minimise inductance but wires will probably work ok if you keep them short.
     
  7. Xracerx13

    Xracerx13
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    besides a 1n4003 that i don't have in stock, what else can i use?
    i have 1n4004 and 1N4001 and 1n4148 and 1n914.
    I measured the mv1y and apparently the side with the white dot is the negative.
     
  8. bob85

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    you can use most silicon diodes or the base emitter junction of a suitable bipolar transistor, not germanium or schottky diodes,
    any of the 4000 series should work.
     
  9. Xracerx13

    Xracerx13
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    Just in case this post is read meticulously I want to correct what i wrote accidentally C126 and C127 are now ruffly around 1000pf.

    I will try my local parts place for a 1n4003 since i need other stuff :D, if its a no go I will use the 1n4004. thanks Bob85.
     
  10. Xracerx13

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    Got the bias diode in just now. I used a 1n4004 and I was quite surprised that the Bias setting jumped down from 75ma to 35ma just from the addition of the diode.
    Its hooked up correctly. Is this normal?
    I'm waiting for the radio to warm up before I reset it to 75ma again.
     
  11. bob85

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    Yes that's normal, idle current should be easier to set & more stable.
     
  12. Xracerx13

    Xracerx13
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    The final bias is most certainly easier to set & more stable. I also installed my home made 10.695mhz crystal filter built using a CBC International schematic and that works great. I stuck it in C15.. the place CBC calls for rather than C13 as someone else mentioned.
    Looks pretty busy, don't it.

    IMG_20171012_154511.jpg IMG_20171012_155114.jpg
     
  13. bob85

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    looks like you have been busy with the iron.
     

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