I built a hot Cobra 29 for a local boy and he blew it up...

[mr_fx]

Robbing Peter to pay Paul is the issue, not knowing how to do this modification.

Where are you tapping this voltage from?

robbing peter to pay paul? that makes not sense... I know how to do the mod, I have done it several times... but I am not going to re-invent something that works... why would I?

you don;t have to tap anything... just use the internet like me, it's pretty simple... you are kinda over thinking the situation...
you basically remove a few components, build the biasing network, add a few caps, solder everything in, retune and you are done...

it has worked several times... and it will continue to work for as many radios as I choose to build.

the Mosfet conversion in the Cobra 29 is a tried and true setup, very popular for many reasons.

 

[mackmobile43]

robbing peter to pay paul? that makes not sense... I know how to do the mod, I have done it several times... but I am not going to re-invent something that works... why would I?

you don;t have to tap anything... just use the internet like me, it's pretty simple... you are kinda over thinking the situation...
you basically remove a few components, build the biasing network, add a few caps, solder everything in, retune and you are done...

it has worked several times... and it will continue to work for as many radios as I choose to build.

the Mosfet conversion in the Cobra 29 is a tried and true setup, very popular for many reasons.

*MPOWER is much better at this

Now lets see if you can try a duck this post with a half witty reply?

Where does this bias circuit get it's power from in this radio?

 

[mr_fx]

*MPOWER is much better at this

Now lets see if you can try a duck this post with a half witty reply?

Where does this bias circuit get it's power from in this radio?

I place the biasing network in place of R56... so that should about answer your question... that is where most people install the biasing network (be it pre-built (ie EKL-1230, or home made, there are a few designs for this...)

this seems to work fine... is that the answer you are looking for?

if you are asking me if I volt the finals... the answer is no, I do not... there is just no reason to do so on the 29

 

[mr_fx]

GREAT NEWS!!! turns out he radio is FINE... got it on my bench, my dummy load, my meters, my power supply... NO issues... still doing the same it was before

hooked it up to my base antenna... still sounding good to the locals...

so much for the radio being junk...

he picked up a 4 foot firestick wanna be with coax and mount (for a truck) he is in a metal work trailer, so that is going to work out just fine...

I am going to go by and tune the antenna for him later today...

seems some of you jumped to conclusions... I still don;t get why it only showed about 15 watts in the truck? getting a solid 48 over here on the dummy load and the same on my old A99... so I don't know

I decided to test my buddy's meter against mine and got the same results... just a little less than 50, but a little more than 45 watts on the PEP scale

so who knows... maybe there is a problem in my friend's install in the truck? my money is on the 3 puck mag mount he runs...

 

[mackmobile43]

I place the biasing network in place of R56... so that should about answer your question... that is where most people install the biasing network (be it pre-built (ie EKL-1230, or home made, there are a few designs for this...)

this seems to work fine... is that the answer you are looking for?

if you are asking me if I volt the finals... the answer is no, I do not... there is just no reason to do so on the 29

So when you remove R56 you have 12 volts I'm assuming which is ok to try and regulate down to a useable 4 to 6 volts you need to bias the mosfets but on the gate you can make the voltage goes as high as twenty volts so what's wrong with volting? Since you only have 13+ volts to work with this is not possible without using a 24 volt power supply and then regulating it down to a manageable level as most of the other components in the amp stage of the radio will not handle more than 16 volts, such as capacitors.

So isolating the higher voltage for the output mosfets would require it's own regulatory circuit but on the other hand not necessary since the mosfets rate of gain over the typical Bipolar transistor is superior but then there is the issue of heat that the mosfet produces due to that gain so is there an additional heat sink added?

 

[mr_fx]

but then there is the issue of heat that the mosfet produces due to that gain so is there an additional heat sink added?

I have not had issues with heat to be honest... but I have considered a heatsink or even bonding the current heatsink to the back plate of the case... not sure how well it would work, just tossing the idea around

not to mention the mosfet tends to run cooler watt for watt

 

[mackmobile43]

I have not had issues with heat to be honest... but I have considered a heatsink or even bonding the current heatsink to the back plate of the case... not sure how well it would work, just tossing the idea around

not to mention the mosfet tends to run cooler watt for watt

How can you say this when a Bipolar transistor biased in class ab has only .6 of a volt applied to the base and a mosfet has a full 4 to 6 volts of bias applied to the gate?

 

[mr_fx]

How can you say this when a Bipolar transistor biased in class ab has only .6 of a volt applied to the base and a mosfet has a full 4 to 6 volts of bias applied to the gate?

just observation... every mosfet based device I have used has ran nice and cool... now I realize my observation can be flawed... but that is just wat I have seen

 

[jon666]

re

i still want a hot rod Lincoln

 

[GLR]

i still want a hot rod Lincoln

We all do.

[youtube]vGpr-Zy_wRs[/youtube]

 

[mackmobile43]

There should be a "yeah what GLR said" button on this forum.

dude you are ate up... I am putting you on the ignore list... you have WAY too much time on your hands. BYE BYE