I have the components but don't have instructions to install on a 148 nwst if anybody knows how or has instructions it be greatly appreciated
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irf520 mod on cobra 148 nwst?
- Thread starter pimphand442
- Start date
here is the only mosfet sheet for the 148 I know of for know. it states for the 4 pin mic radio only. so not sure about the 5 pin.
http://www.cbtricks.com/miscellaneous/fet_papers/ekl/graphics/erf2030_148gtl_mod.pdf
http://www.cbtricks.com/miscellaneous/fet_papers/ekl/graphics/erf2030_148gtl_mod.pdf
just thought of something, is your radio working fine with the final that is in it?
the mosfet is not that good on SSB when it is a addon. as staybolt said it will make it sound bad.
do not change the stock final if you are just looking for more power output. the only person that would know you are putting out a few more watts would be you. it will not show on the receive radio. the only way that would give more on receive if you went to 100 watts.
in fact buy yourself a rm kl203 small amp and it will do what you would want and about the cheapest wattage around.
Two suggestions, first if the radio works LEAVE IT BE and give it a proper tune & alignment. A cobra 148 was never intended to be a 30 watt radio so don't try to make it something it's not. Even if the final is blown find a replacement 1969 and go that route.
Last, I do notice the radio is a soundcrapper. They have a long list of performance issues that have been well discussed. When you have that radio tuned set it for 8-10 watts peak. Any more and the regulator cannot keep up and the audio goes to crap. This can really be heard on SSB.
In closing a mosfet mod in a 148 is not suggested. If you feel you must I guess it's better to destroy a soundcrapper then a Philippines built classic. Your radio your call.
Last, I do notice the radio is a soundcrapper. They have a long list of performance issues that have been well discussed. When you have that radio tuned set it for 8-10 watts peak. Any more and the regulator cannot keep up and the audio goes to crap. This can really be heard on SSB.
In closing a mosfet mod in a 148 is not suggested. If you feel you must I guess it's better to destroy a soundcrapper then a Philippines built classic. Your radio your call.
I don't use this radio bc it is a sound tracker but I wanted to test out the irf520 mod and it would be just an experiment radio although it does have the xtra channels added to it but again just an experiment radio.... thanks,
I used the mrf520 as final and used en-396-dr and I got a dk og 8 watts and swing to 35 and almost 50 out of ssb and tht was with a stock 2166 as a driver now I changed the 2166 to a 2029 final and adjusted the bias and results were 11w dk and 48-50 watts on am and on ssb about 65 surprisingly it performed really well on ssb got good reports back that was a shocker I read that mosfets are horrible on ssb now that's with the power almost all way down if I lower dk anything below 10w the am swing stops at 40 bt haven't changed any cap values yet I was getting late lastnight so ill have to try messing around with different values later. any thoughts on this or ideas to try im all ears its just an experiment radio if it goes poof owell lol thanks all 73's
before you play with it too much you might want to verify the output freq from the radio. say you are on 27.185 channel 19 it should read the same with a external freq counter to keep it sounding good. you start changing caps to get more out of it the freq may start changing on you. just be aware of this.
If it's really doing 65 watts peak, I'm very surprised you haven't let the smoke out yet. Look at the size of all the output components after the final in that radio. Notice all the puny little ceramic disk caps in the coupling and tuning stages? They can't handle the RF current or voltage produced at this power level and could easily arc over. The slugs inside the output and 54 Mhz. trap inductors must get smoking hot and probably lost their permeability.
Another thing people forget is these radios are not relay switching and they don't use expensive PIN diodes to switch the antenna between the transmitter and receiver. You'll find most CB's connect the receiver to the antenna through another very small cap that is designed to drop most of the transmit RF voltage across it and protect the receiver when the transmitter is on. Flash this capacitor and you'll trash the front end of the receiver real quick. I suggest we not try and get this much more power out of an existing stage since nothing was designed to handle it from the DC path feeding the final to the output circuits following it.
the back of the radio gets warm but not hot it looks like the person before me had changed a bunch of resisters in the driver and final area the resisters are bigger than the rest around it and some caps and some diodes and a couple 2999 transisters are installed my other 148 nw st has small resisters in the driver and final area also my other stock 148 has 2 ceramic disk capacitors on the soldier side of board and this one that I put this irf 520 in didn't however the tunning slug gets pretty warm when you touch it while in tx mode for some reason I think it even shocks/burns my finger when I touch it in tx what is a good dk for this radio I might have to change a resistor to the final to lower dk I was just aiming for practice on this radio but would like to learn the right way so wouldn't mind turning it down I just like to watch that meter swiiiing thanks all