DX 959 modded to dual finals... NO gain on the meter???

[mr_fx]

I started with a DX 959 (the newer one with mosfets from the factory)
I did not design this mod, I just copied the work done in Loosecannon's thread


This is what I did:

Q48 (IRF520)
D91 (5V6) (I took this from the DRIVER, replaced the driver with a 1N4148)
R242 (100K)
R243 (47K)
L34 (1K) ((resistor with ferrite bead on one lead, I used 1/2 watt since that is what I had. the other side is using 1/4 watt?))
C209 (.0015uF, used a pair of Ceramic disc parts)
C211 (.1uF, Mylar)
C212 (.1uF, Mylar)
VR11 (100K, Radioshack)
L35 to 4 turn, for this I just made the stock one shorter

The gate voltage is set to around

After that I powered up and tested it on the same meter. On AM I saw a drop in power, making around 24 watts PEP, as well as a lower dead key

Anyway, it's making around the same on SSB

I retuned the TX, circuit gate voltage is between 3.55-3.65 on the finals and the driver...

Everyone says it sounds real clear, it's just not making much power.

I must have missed something. Any ideas?

 

[wavrider]

I usually do not mess around with any power mods, just tune the radio for the cleanest ( on the scope) audio, 100% modulation with the mic gain wide open, then if it needs any more power I tell the owner to get him one of them there linears. That way he will have a clean signal if he decides to use an amplifier.

By tuning for max smoke on a meter instead of an o'scope it just invites splatter and QRM on the bands, low dead key max swing is an equation for SH*T audio.

Some mods do work well, and in the case where the final is no longer available and a mosfet is then installed the same goes, tune it for CLEAN audio on the scope and 100% modulation.

The rule of DB gain. It takes four times the power out to increase a signal by 6DB or one S unit. If the stock radio is 20 watt PEP then it will take 80 watts PEP to make one S unit on the receive end.

Sometimes those mods just do not do a whole lot of anything but show swing on a meter that is probably reading the transmitted RF frequency and all associated harmonics combined. Not saying the mod you are performing is not a good mod, just stating in a general manner about power mods.

Many ham rigs have 2sc2879 finals, a pair of them, yet max output ( unless messed with) is 100 watts PEP. they can be turned up to 150 or sometimes 200 watts PEP output, but by keeping the power out to 100 watts it keeps a clean signal and does not harm the bands with splatter.

 

[mr_fx]

wavrider I couldn't agree with you more however I am trying to keep busy.

I am well aware the low DK high swing = garbage.... that's why I am worried about this. Why would the AM Dead key get lower with dual finals?

also I think one of the final adjustment pots is screwed up. It's not working very well.

 

[mr_fx]

well I disconnected the OEM final and it remained the same ... so it looks like the OEM single final died?

 

[Robb]

I would only add just one thing to what wavrider said. You can tune up the TX coils for max output. They are really just an impedance matching network and can be legitimately peaked. But as far as the AM modulation or the SSB/ALC, keep them close to factory/less than 100%.

Don't disable the 3rd harmonic coils near the back of the radio - by smashing them/widening them down either. Leave them INTACT! That will DEFINITELY make for a nasty signal that will DEFINITELY get amplified if monkeyed with. You really don't need or want that. Remember - crap in; crap out!

For better signal running less than 100% modulation on AM and SSB, get a TopGun compressor module.
Much better/fatter audio and no distortion to get amplified.

Forget clipping the limiter too.
That should go w/o saying.

 

[mr_fx]

thanks Robb, it sounds like we have similar ideas on what to do here. I never clip limiters, or mess with harmonics coils... I have been trying to explain to people that while spreading those coils will make your meter read higher, it is not in the target frequency, so it's just basically noise

I was thinking about the Top Gun as I have read good things about it

I figure a dual IRF520 should do a solid 35-45 watts

 

[mr_fx]

The following quote is from CB Radio Talk forum:

When I modded my dx 959 i bought the proper 5.6v zener diode to go across the driver...and as a hint I can tell you to compare the schematic of a dual final galaxy base with the 959...if you give me a bit here I will go over what I added..I have to dig up the file I put it in...I had a 40+ watt output on ssb and pep on am..so I do know it works and works very well with no backswing on avg power.

The reason for the proper diode is biasing etc..I wont go into details but it is basically a clamping diode and a 1n4148 have a .7v forward drop and no reverse bias pass through unless you get into the breakdown region..where as these zeners regulate at 5.6v..try that and report back...I bet you will find it may fix your issue.

Good call! I threw a 6.1v zener in there (I have a 5.6v on order) Anyway, I had to rebias the driver, but it is running a solid 45 watts! That will do, before I was lucky to hit 25 with 2 finals, and barely got 20 with the single final, this should help out a little bit I think, and I am not so bored anymore

 

[freddbro]

Can I do A Duel Final Installation,which I would believe is a Paraell final
transistor, along with a 5.6 Zeiner Diode to get more output from my
Cobra 2000 or Pres. Wash. ??? Thank You..Freddbro@aol.com

 

[mr_fx]

you can do all sorts of things.but in the case of the 959, there is already a spot for it and all you need to do is add the components to the board

 

[9C1Driver]

Can I do A Duel Final Installation,which I would believe is a Paraell final
transistor, along with a 5.6 Zeiner Diode to get more output from my
Cobra 2000 or Pres. Wash. ??? Thank You..Freddbro@aol.com

Remember, classic old school Cobra 2000's, Washingtons, and Madison's were never intended to be 40+ watt radio's. They are outstanding sounding 12-18 watt radio's. Don't hack one all up with crazy new mods. If you need MOPOWA get an amplifier.

Also realize that if you do perform a power mod you better up-grade or change the power supply. The stock supply cannot keep up. I guess if you want a heavily modded (destroyed) Cobra 2000 go for it, it's your radio. Don't be surprised though if you ever go to sell it the value will be half what an original radio would be.

 

[Zman]

Not much you can do for the 2000. It doesnt even have a VR pot for the power supply. I had one once and i just left it be. Besides my amp was MUCH happier with a low powered rig running into it!!!!