Hi guys.
Is it already converted? A friend sent mi that amp to do conversion, but it seems it's already done.
Mike
Is it already converted? A friend sent mi that amp to do conversion, but it seems it's already done.
Mike
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New 667V issues
- Thread starter sp5it
- Start date
Thanks for the Pic...
This is that mod where the area is, what those Vids show...
In that amp they show they are soldered...so to prevent another problem...
Turn the amp on it's side and look at the board - side view - to make sure they did not PUSH those caps into the HEAT SINK - shorting out that section - preventing it form working - shorted out the input - kinda' thing.
This is that mod where the area is, what those Vids show...
Turn the amp on it's side and look at the board - side view - to make sure they did not PUSH those caps into the HEAT SINK - shorting out that section - preventing it form working - shorted out the input - kinda' thing.
I got a problem with that amp.
When transmitting to dummy load or antenna SWR goes sky high. No matter AM or SSB.
Amp is brand new, no sign of any damage.
Anyone saw that issue before? Parasitic oscillation, bad relay?
Mike
When transmitting to dummy load or antenna SWR goes sky high. No matter AM or SSB.
Amp is brand new, no sign of any damage.
Anyone saw that issue before? Parasitic oscillation, bad relay?
Mike
It appears as though there are no tuning capacitors on the output side of the amp, nor is there a tuning capacitor between the driver and the finals. I'd suspect that's the issue. Unfortunately, Texas Star has really dropped the ball when it comes to the new amps, they just throw the DEI transistors in and don't bother to re-tune the input and outputs, and the DEI's do NOT tune the same as the old Toshiba transistors. Looks like you're going to have to some re-tuning to do.
~Cheers~
~Cheers~
Ok, after some diagnosis it is oscillation for sure. After 30MHz lowpass SWR is fine.
Could you point me where to look for a tuned circuit sample usage? Maybe I could copy that circuit from other amp?
Mike
Could you point me where to look for a tuned circuit sample usage? Maybe I could copy that circuit from other amp?
Mike
Where are the collector emitter caps ?
did somebody forget to fit them or do they not bother anymore.
did somebody forget to fit them or do they not bother anymore.
Handy Andy is indeed right, that does not look correct. Here are the spots that you may need to add capacitance. The first set of arrows in white is at the input, the yellow set is at the output combiner, the green set is between the driver and final section. It's best to use a 465 ARCO adjustable compression trimmer capacitor to dial things in, then swap out to mica capacitors (@500V) of the value you dial it to. I've had to do this on a few 667's with SWR issues, and they've all come out very well. Also, the driver section circled in light blue is absolutely the worst, most garbage design I've ever seen, and likely the culprit of all of the oscillation/SWR issues you're having. Old 667V's had a 2SC2290 in place of the MOSFETS, with proper biasing at the base of the 2290... these FETs don't appear to have any sort of real bias on them at all... trash.
~Cheers~
~Cheers~
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I've been doing comparisons,
Because if this is something new, I'll need to learn this too...
And the other half of mainboard
Several things...Because if this is something new, I'll need to learn this too...
And the other half of mainboard
One, Location of R3 and what it's connected to - 75 ohm - Power?
Note 4 states; Trace is cut, R3 covers that section...
I'm working this right along with you...unfortunately I don't have a REAL one in front of me to help...
Considering what is on You Tube, makes me wonder if they "make changes" and randomly alter these parts...
The MOSFET input section DRIVER - to the amp, scares me...
