X-Force 600HD Smoked

[Shadetree Mechanic]

Shade, Just out of curiosity, what’s the amp producing now with the lower drive and less voltage?

Also, is there a reason you dropped the voltage on the radio as opposed to just dropping the RF power? Granted I only use mine on SSB, so I don’t have to worry about changing the carrier...but it works for me.

With the lower drive and less voltage, the amp is putting out about 450w peak as opposed to 600w peak before. The reason for dropping the voltage on the radio is that the power adjustment knob only adjusts the carrier power. It would swing to 70w from any dead key setting. There is an AM high power adjustment inside the radio but I think it just adjusts the highest dead key from the front of the radio. I was told that it was peaked and tuned at Bells CB by the guy that I got it from so I don't know if this is how they operate out of the box. So basically dropping the radio voltage down to 10.5v I was able to get 40w peak out of the radio. This is working out great on AM but SSB has the amp relay trying to shut off between words because the drive is too low. I don't want to turn it back up for SSB because I don't want to have to change a bunch of things to switch back and forth because I switch back and forth a lot. I will probably put a remote key relay in the Stryker and have it key the amp directly. Now I just have to figure out how to do that. And that's the fun part.

 

[2NC995]

With the lower drive and less voltage, the amp is putting out about 450w peak as opposed to 600w peak before. The reason for dropping the voltage on the radio is that the power adjustment knob only adjusts the carrier power. It would swing to 70w from any dead key setting. There is an AM high power adjustment inside the radio but I think it just adjusts the highest dead key from the front of the radio. I was told that it was peaked and tuned at Bells CB by the guy that I got it from so I don't know if this is how they operate out of the box. So basically dropping the radio voltage down to 10.5v I was able to get 40w peak out of the radio. This is working out great on AM but SSB has the amp relay trying to shut off between words because the drive is too low. I don't want to turn it back up for SSB because I don't want to have to change a bunch of things to switch back and forth because I switch back and forth a lot. I will probably put a remote key relay in the Stryker and have it key the amp directly. Now I just have to figure out how to do that. And that's the fun part.

Good deal, Chris. As always, thanks to you for sharing your thoughts, results and the journey to get there

I know it’s been mentioned....but since modifying my Lincoln I’m a huge fan of a direct key. Mine is a slightly bastardized arrangement...but I love that the amp is instantly keyed when the PTT is in and instantly off when I let it go.

I want to never deal with another RF keying arrangement in my life

 

[kopcicle]

Wouldn't have it any other way

 

[2NC995]

Wouldn't have it any other way

Imo..the number one thing missing from “exports” and “cb” amps.

And CHEAP to implement.

 

[loosecannon]

shadetree,

turning down the voltage supply to the radio seems like kind of a drastic way to decrease the power. changes lots of things about how the radio operates including what the bias current on your driver and finals is with that new setting.
from the factory these are set by monitoring the idle current going into the radio when keyed up on SSB with no audio input.
when you lowered the voltage, you changed that voltage/current relationship.
hard to predict how much (for me anyway).

you should be able to use the internal VRs in the radio to get what you want.

use the AM high and low power VRs to set the deadkey range you want.
set the AM modulation with your scope.

then use the mic gain on the front of the radio to tone down the peaks.
you may find that you only need to turn your mic gain up to around 9 o clock to get the 40 watts PEP you are looking for.

also, on SSB, your mic gain is the same thing as a variable RF power control, so use it that way when on SSB.

once you find the settings you like, just turn the mic gain knob where you like it for each mode.
LC

 

[Crusher]

Just a heads up, should be 500pf across the input transformers. If not, it will never Tune flat. Also, if you can tune flat with trimmer. I also try to overcouple by about 20pf. Seems to clean up signal some.

 

[Unit 194]

The 600HD was the topic of conversation on the Owners of X-Force Amps Facebook page. https://www.facebook.com/groups/OwnersofXForceAmps/

 

[Shadetree Mechanic]

shadetree,

turning down the voltage supply to the radio seems like kind of a drastic way to decrease the power. changes lots of things about how the radio operates including what the bias current on your driver and finals is with that new setting.
from the factory these are set by monitoring the idle current going into the radio when keyed up on SSB with no audio input.
when you lowered the voltage, you changed that voltage/current relationship.
hard to predict how much (for me anyway).

you should be able to use the internal VRs in the radio to get what you want.

use the AM high and low power VRs to set the deadkey range you want.
set the AM modulation with your scope.

then use the mic gain on the front of the radio to tone down the peaks.
you may find that you only need to turn your mic gain up to around 9 o clock to get the 40 watts PEP you are looking for.

also, on SSB, your mic gain is the same thing as a variable RF power control, so use it that way when on SSB.

once you find the settings you like, just turn the mic gain knob where you like it for each mode.
LC

That's a good point about the bias. The owners manual says it is designed to work on any 13.8v source and the alignment procedure also specifies 13.8v. I don't know if the bias power comes from the regulator in the radio, it seems that it would need to be independent of the fluctuations of the incoming power. It might not do too well with 10.5v, that's pretty far from the expected voltage. Maybe I will turn it up to 12v and see what I get for output. I have thought about building an attenuator into the input of the amp, probably wouldn't take much. I have heard about the audio level being the side band power, but have not really tried it on AM. I will play around with it to see what I can get. Probably start looking for a bigger amp that can take this amount of drive.

 

[Shadetree Mechanic]

Found this video about changing pills. I should have watched this before I did mine.

 

[Shadetree Mechanic]

I finally got back into my main shack to play with this some more. It seems the station at the workbench in the back room is more entertaining when no skip is running.

I turned the voltage on the radio supply back up to 12v and attempted to get everything set up correctly. I got the amp input tuned to a hair over 1.1 so I am pretty happy with that. The amplifier output will still need some work.

With the radio at 12v and the amp at 13v (that's the lowest it goes) and a 5w dead key out of the radio, I get 150w out of the amp and an SWR of 1.7. Now if I raise the dead key to 200w, I get an SWR of 1.5. If I try to lower the dead key to 50w then the SWR is 2+. When modulating, the SWR will go up a few points. I didn't try it from 50w though.

With the reduced voltage on the radio, it seemed to really help the amps output tune. Maybe I will try a smaller radio just to see. I was hoping that the input tune would fix the output tune as I have seen with my Texas Star amps, but this is not the case. I will be ordering a trombone capacitor to see if that will get me where I need to be.

Does the SWR level going down with a higher dead key indicate the output tune needs work like I am thinking? What do you guys think?

 

[Shadetree Mechanic]

I got some play time with the amp today after work. I have not powered it up yet, just wanted you guys to look at it first to make sure I didn't do something wrong.

@loosecannon I got a second trombone, and I would like to see if you could freshen up my Madison too. I will be sending you a PM soon.

I installed the trombone on the output. Made some legs out of 12awg copper wire.

I had to move one of the rail capacitors to the other side.

I attached it to the output with a piece of 18awg wire.

 

[Shadetree Mechanic]

I set the trombone with my Chinese component checker and tried it out. It seemed that the pills were getting warm with no load on them. Keyed a few times and pulled the trombone out a little.

Then when I went to pull it out a little more, my wrist brushed up against the amp next to it and the trombone felt like it was 300 degrees....

I unplugged the supply real quick and felt around inside the amp. The trombone was cold. I had a burn on my finger from the edge of the tube. Apparently I was able to make the transistors conduct. How did I make them produce an RF output without being keyed? Maybe the resonance of the circuit was making it oscillate.

For further trombone tuning, I unplugged the supply. I ended up with the trombone about half way out and the pills no longer get warm on standby. So now it is apparent that the output loading can affect the bias of the transistors. The AB bias maybe contributed to my first hand experience? I wonder if class C would behave this way too?

The trombone tuning on the output had an effect on the input tune too. But in all cases, the input adjustment was the best it could be in the original spot.

This arrangement produced a best SWR on the output of 1.7 so not much of an improvement. The input SWR on side band is now over 3 but is less than 1.5 on AM. So I started thinking about a tuning coil like what I have seen on some of the bigger amplifiers.

 

[Shadetree Mechanic]

I used some 1/8 inch HVAC copper tube and wound some coils around my pen light. So from left to right we have 4.5, 3.5, 2.5, 1.5 and 1 turn coils. I picked the 3.5 and put it in with the trombone connected at the coil output.

So now I am able to adjust the input trimmer to improve the input tune over the adjustment range of the output trombone. I was able to adjust the trombone so the output tune was around 1.2 and the max power was around 400w. Then one time I keyed up and the amplifier didn't un-key.

AAAAHHHH!!! PULL THE PLUG!!!

Note: When the amp does this it also wipes out the receive.

So I pulled the trombone back out to the mark I had about half way and started the adjustment routine again. I am unable to do better than 1.7 on the output. Its really strange though. When first turn the amp on and key, the output SWR is about 1.2 for a few seconds. Then after that it always jumps up to 1.7 so I am not sure if I just need more tuning range? I am going to start spreading the coils next to see if there is a sweet spot.

Also of note, the input SWR on sideband now stays good with the coil in the output so I must be doing something right?

So my big questions are:

1) Is the initial output SWR of 1.2 that then jumps up to 1.7 by itself an indication of anything? Like I am right on the edge of a proper adjustment?

2) Is the output tune adversely affecting the input tune on sideband and not AM an indication of anything?

3) Am I going about this whole thing in the right way or should I be going in a different direction? Like the tuning of the output transformers themselves?

Thanks for reading all that, any and all replies welcome.
Chris

 

[2NC995]

Is the bias on all the time, Shade, or switched by relay or transistor?

I'm very surprised at the RF when not keyed also.

 

[Shadetree Mechanic]

Is the bias on all the time, Shade, or switched by relay or transistor?

I'm very surprised at the RF when not keyed also.

It looks like the bias is switched with the relay so it would not be on in standby. Maybe it was when the trombone was in too far and the transistors were getting warm like they were conducting? If they were conducting, it wouldn't have been DC to burn my finger so it must have been some kind of RF. This is a Benjamin Franklin moment for me. haha