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AD203 Revisited

U

unit511

Member
Jan 21, 2012
51
10
18
I have installed a RM ad203 mosfet board in a trc453 radio in the past..... the radio crapped out and I had this board with no home. I could not just leave this thing alone. I had to play. I took the guts out of the trc453 and kept the AD203 in it. I bought a used trc453 off of ebay... but that is another day of playing. I bought a new meter to check swr and power . I am still running a Gainmaster with very low swr at 4.5 watts. on my CB's. The AD203 is only giving me 35 watts ssb and 10 watts am. I saw a video on Utube that will increase your wattage but if u think about it for awhile the power increase seems way too high for the board. So I will not cut r1 and jump to r3 and r4. I would more likely change the mosfets to a higher output mosfet. I would also think about cleaning the signal up. I would hate to sound like channel 6 apple splatters.
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Hey ROBB it's me Unit 511 from our contact on lower 39 on 2-6-2015 at about 5:00pm. I hot glued the switches in so it looks like a regular cb. I could spray paint the hs and hide it a bit I guess.
 
OK; now I see what you were talking about. Conditions were in and out when we were talking this afternoon, so I couldn't grip what you were saying at the time. Now it makes sense.

That's different. Honestly can say that I've never seen anything like this before.
73
 
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Your better off trying to find out why the amp will not work like it should, swapping mosfets would be an even bigger headache and disaster. You would have been money and time ahead just buying a KL-203 in the first place.
 
To replace all of the MOSFETs in this thing is not an expensive venture, you can buy them for a buck apiece. Soldering skills and knowledge of circuit biasing would also be necessary . . .
 
Robb do you think that board can handle and upgrade from the RM-3's with no other mods? I kinda doubt it. Most of those small RM italy amps and boards are throw away when they break.
 
9C1Driver said:
Robb do you think that board can handle and upgrade from the RM-3's with no other mods? I kinda doubt it. Most of those small RM italy amps and boards are throw away when they break.
Click to expand...
Good question.

I'm guessing here:
1) 13n10's used for replaceming/upgrading the MOSFETs from the RM-3's.
2) Gate voltage should be OK but should be checked.
3) Impedances should be the same or close, as MOSFETs usually have very high impedances.
4) Don't know anything about the input gain requirements; that is the one grey area here AFAIK.
5) Might have to add/remove some capacitance for the MOSFET input/source.

Ummm - yeah; why not?
Be interesting to find out - eh?

If it cost ~$3 to fix; then it isn't a tosser . . .
 
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Gonna drop in 4 new irf520n's. Really cheap on ebay. Will check output and deal from there. Don' t know much bout tronics but learnin'.
 
unit511 said:
Gonna drop in 4 new irf520n's. Really cheap on ebay. Will check output and deal from there. Don' t know much bout tronics but learnin'.
Click to expand...
Going to install mini 12v fan where mic connector was....also a multicolor led to on /off switch.....Robb gave me the idea to go with different mosfets so I will try them. The old mosfets were a struggle to remove. I will have to fix up some trace on the install. Like to get some watts out that I can talk about.
 
There is no guarantee that anything but RM-3's will replace them exactly. This might not work as expected. But as an experiment it could probably be made to work so long as all of the requirements for balancing the circuit input/output/voltage are met.

Be interested in hearing what you find out . . .
 
That's a kl203 board, 100w is usually no problem if they are working as they should,
5w input should get 50w+ output, but i would want a better heatsink if you run it that hard,

check the input divider resistors are the same as in the kl203.

RM3'S perform better than irf520's in those boards if they are working.
 
bob85 said:
That's a kl203 board, 100w is usually no problem if they are working as they should,
5w input should get 50w+ output, but i would want a better heatsink if you run it that hard,

check the input divider resistors are the same as in the kl203.

RM3'S perform better than irf520's in those boards if they are working.
Click to expand...
it's all good...just playing with stuff.
 
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Dropped in new 13n10's. Terrible output with high swr. Needs tuning?. No heat generated from transistors - hs cold. Added light to on -off switch so I know voltage present. Tried thermal pads on backs of mosfets but blew 6.3 amp fuse on board. Removed pads and fuse. Works again. But unit needs adjustments or proper mosfets...
 

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