Texas Star DX 400 Input SWR

[TheRealPorkchop]

I’d try those two trimmer caps you have then and see what happens. With one of them you should find a happy median between the two. Or hopefully anyway.

If not, gots to be some koolaid in there from a previous “tech”.

 

[Shadetree Mechanic]

I’d try those two trimmer caps you have then and see what happens. With one of them you should find a happy median between the two. Or hopefully anyway.

If not, gots to be some koolaid in there from a previous “tech”.

I tried the 468 and it was worse. In the middle of it's adjustment range I got the relay to chatter. The will try the 462 next. My DX350 is the amp put usually run in this position where I am testing the DX400. The 350 ended up being 1.1:1 with this procedure. I fixed up the power wire on the 400 with some 8awg.

We don't need no stinking fuses. Lol I run a fuse on the supply connection.

 

[TheRealPorkchop]

Ditto on the fuses.

Like I said, might be some magical koolaid in there somewhere. You’ll have to check it out and see, might be something hidden somewhere that you’re overlooking. Try a 33pf and see what happens

.

 

[nomadradio]

The 468 capacitor has a minimum-capacitance setting that was probably too large, and won't go down to 120 pf. Probably worked best with the screw loosened entirely.

Try the smaller one and see if it won't work better.

And if the 462 adjusts full-tight (max capacitance) before showing a minimum input SWR, you could put a 47pf or 68pf silver-mica cap in parallel with it, to extend its upper adjustment range.

Odds are that a 463 or 464 would adjust more smoothly, nearer the center of its coverage range.

73

 

[Shadetree Mechanic]

The 468 capacitor has a minimum-capacitance setting that was probably too large, and won't go down to 120 pf. Probably worked best with the screw loosened entirely.

Try the smaller one and see if it won't work better.

And if the 462 adjusts full-tight (max capacitance) before showing a minimum input SWR, you could put a 47pf or 68pf silver-mica cap in parallel with it, to extend its upper adjustment range.

Odds are that a 463 or 464 would adjust more smoothly, nearer the center of its coverage range.

73

I just tried the 462 and it pegs the SWR meter full scale. I will put in an order to RF Parts for some 463 and 464 caps and a few other odds and ends that I need. Thanks.

 

[TheRealPorkchop]

That sucks.

 

[Handy Andy]

Better check soldering too...

Because if the ferrites are not fully connected...there will be SWR issues...I see green but not sure if that's from the wire reflecting off or if that "Fuzz" is corrosion...

 

[Handy Andy]

With the 400 - there are several changes...

Go here...
http://www.cbtricks.com/Amp/txstar/dx400_dx500/index.htm

This may help you rebuild that miracle...

 

[Mudduckmobile]

Better check soldering too...
View attachment 25205

Because if the ferrites are not fully connected...there will be SWR issues...I see green but not sure if that's from the wire reflecting off or if that "Fuzz" is corrosion...

Good eye ballen. That looks like a bad spot for real.

 

[Shadetree Mechanic]

The coax and cap go straight to the output SO239. I really should get one of those magnifying lamps. It is next on the list. The whole thing could use some cleaning. The guy had it on the floor of his car and it looks like it got damp. What would be good to clean this with?

 

[Mudduckmobile]

The coax and cap go straight to the output SO239. I really should get one of those magnifying lamps. It is next on the list. The whole thing could use some cleaning. The guy had it on the floor of his car and it looks like it got damp. What would be good to clean this with?
View attachment 25207

Looks like a good cleaning and rebuild is in order...Fun way to learn.

 

[Handy Andy]

Ford Escapes Clearance?

Was the Ford Damaged?

Does it have a leaky roof?

Seeing some "high water" marks in there.

This may be a lost cause - water entry is never good...

 

[nomadradio]

At least it's not tall enough to star in any "11foot8.com" videos on YT.

73

 

[loosecannon]

just scanned through the thread and it looks like you are not having much luck with the tuning caps.

just as a lark, check the value of C3 in your particular amp. This is the DC blocking cap on the input.

the schematic shows it to be a 1000pF (.001uF).
I have seen chassis with a 2000pF (.002uF) here which would be less resistance at 27mhz.

If this cap has gone low in value, due to the amp having been hit with a large deadkey or other calamaties, this cap could be causing you issues.

lift one leg and check its value.
again, just a wild guess in case you hit a dead end.

also, be sure to use a different radio, using all the same coax, in order to determine if you have a radio that has problems with its output filtering.

for example, if someone turned that 54mhz slug in the back of your madison, then you could have more output at 54 mhz than an amp wants to see.

If you have one radio that always seems to give you a high input SWR when using an amp, the radio itself could be the reason.

also, 464, or a 465 are the trimmer caps to try with this chassis.
LC

 

[TheRealPorkchop]

That’s really good info, I learned something there LC.