TX Star 250 dx SWR ? (Something lost it's value ?)

[Switch Kit]

Swr this and that fine and dandy , still have the same problem I have been addressing . Something is obviously out of wack in the tuning section ? , looks like I'm on my own from here ? Much thanks as always for any input that came my way on this one . Thanks much. Switch

 

[SIX-SHOOTER]

I'm just giving you a hard time, but now I am curious... If my swr meter reads 1.1 on 20 meters, and 1.4 on 40 meters... is my singular swr 1.25?

You will usually have a different SWR on each band but it's possible that they are the same.I know that you understand how a Standing Wave Ratio actually works but many who will read this do not.My Five Band HF Yagi has a slightly different SWR on different bands as most do but none are bad or above 1.5.1 anywhere I talk.

SIX-SHOOTER
W4KVW
WRMX520.

 

[AudioShockwav]

Does it hang up after you unkey?
Does reducing the drive have any effect?

73
Jeff

 

[DoctorAudio]

If you are getting a high output standing wave on high dead keying, does it drop when you modulate? If so I have a possible solution. Some of the early DX250's and/or Killer Bee 250's ran a lower value mica cap across the output transformer. (430 or 510pf). That in and of itself isn't necessarily a problem but I have seen it happen from this low value. I've also seen this condition on the DX250's with the 1200pf shown in the CBTricks schematic, gets overheated and changes value. See what cap is in yours. If it's a 1200pf, see if it changed value (they usually drop) and if it's one of the smaller values, remove and put in a 1200pf.

 

[Switch Kit]

If you are getting a high output standing wave on high dead keying, does it drop when you modulate? If so I have a possible solution. Some of the early DX250's and/or Killer Bee 250's ran a lower value mica cap across the output transformer. (430 or 510pf). That in and of itself isn't necessarily a problem but I have seen it happen from this low value. I've also seen this condition on the DX250's with the 1200pf shown in the CBTricks schematic, gets overheated and changes value. See what cap is in yours. If it's a 1200pf, see if it changed value (they usually drop) and if it's one of the smaller values, remove and put in a 1200pf.

Much thanks Doc , Your right ! it did drop after modulating ! this surely gives me something to go on ,are you talking about C-16 ? it's 120pf . Thanks again ! Switch

 

[Switch Kit]

Does it hang up after you unkey?
Does reducing the drive have any effect?

73
Jeff

No and No Jeff .

 

[DoctorAudio]

C14 is usually the culprit, especially if it's a Mica (kidney bean).
If C14 tests fine you can always check the value of C16 as well as both of these caps endure a lot of RF current.

 

[nomadradio]

if it's a Mica (kidney bean)

A very good point. And if C14 is a metal mica cap, this is better. The brown silver-mica caps can fail and still look okay. The metal mica almost never fails without showing visible stress.

73

 

[Switch Kit]

Thank you guys again ! I'm feeling it ! I had to order the caps on line ! Damn it ! I remember the days when we had electronic parts stores and even Radio Shack back in the days could have helpful parts in there stores from time to time. I'll let you guys know how things work out next week . (I'm feel'in it !) Cheers to the techs and members of the WWDX willing to take the time and share there experience and know hows with others. Switch Kit

 

[Switch Kit]

Well Doc Audio , you called it as the schematic called for , it fixed the SWR on the high side of the amp. Although looks like I lost about 70 talking watts also ? So appranetly the 500pf worked in these boxes until they got to hot and lost there value , so back in the days , I'm guessing this problem happened to many others as well ? Then Texas Star changed them to 1200pf which is now apart of the schematics (if I'm understanding this correctly ?) Must be more to it with me losing the power as I have ?
Would lowering the pf of the cap help give me some of my power back ? or is it something else ? ........Would just like to say , Texas Star amps over the years for me were pretty much bullet proof with a good SWR , I've seen them beat to death and they still worked ! But this older 250DX doesn't make a whole lot of sense to me. First off the SSB delay would only give you half the power from the box because on the high side of the box the SSB switch needed to be shut off only for the relays to chatter like hell ! Then came the so called mod to fix the problem so you could run the box full power on SSB , (Even that mod aint the best in the world but it helps ) .........What was TS thinking on this from the get go ? Thanks much as always ! It surely fixed the SWR and soemhow chocked some power out. Switch

 

[DoctorAudio]

Yes, you could probably lower it to 1000pf and get "some" of your peak power back but I wouldn't go any lower than that. Besides, some of the power you were seeing could have been ghost watts from the SWR anomaly and not real anyway.
Cheers though either way, I'm glad it worked!

 

[Switch Kit]

The 1000pf worked just fine ! I did get some good swing back on the amp and SWR held strong ! Even put the AM/SSB delay mod back together with no problems that I can see (really holds the power and relay on the high side on SSB and hitting the switch on AM keeps the relays right) Hoping this thread can help somebody else out in the future as it has for me . Thanks Doc and to all that have chimed in. Switch