8 transistor amplifier low power issue

[Ratfink]

I have an XForce 8 transistor amplifier and its only seeing 500 bird average. It is being driven and supplied correctly . It is being ran at 16v and on occasion it will do 600w. It has brand new transistors and everything else in the amp appears to be find I'm guessing I have some sort of a tune issue internally . All tests were done on a dummy load.

 

[Ratfink]

Not a single soul? Wow.

 

[9C1Driver]

What are the drive levels?

 

[Ratfink]

100 average.

 

[Shockwave]

I can't see all the parts of the input circuit sine some seem to be mounted on the inside of the front panel. I do see a resistor that appears to be inline with this circuit and that's a no no on high drive amps. Although I would expect that resistor to be burnt if it were dropping a significant level of RF.

Other issues include small output transformers that are probably heating due to core saturation. Check the last combiner in the output near the coil and relay. It's covered in silicon but if it's the same as all the others, it is way too small for that application.

There could also be impedance mismatch issues anywhere in the circuit. Including the number of turns used on the input and output transformers and the value of caps across them. Is the input tuned right as well as the brass cap in the output? All things to consider that can rob power.

 

[Ratfink]

I can't see all the parts of the input circuit sine some seem to be mounted on the inside of the front panel. I do see a resistor that appears to be inline with this circuit and that's a no no on high drive amps. Although I would expect that resistor to be burnt if it were dropping a significant level of RF.

Other issues include small output transformers that are probably heating due to core saturation. Check the last combiner in the output near the coil and relay. It's covered in silicon but if it's the same as all the others, it is way too small for that application.

There could also be impedance mismatch issues anywhere in the circuit. Including the number of turns used on the input and output transformers and the value of caps across them. Is the input tuned right as well as the brass cap in the output? All things to consider that can rob power.

Input was tuned for minimum reflect back to the driver which end up being 150pf the output was at 130pf and I bumped it up to 150pf the turns are 3 in 3 out and the wraps are counted on the transistor side .

 

[Ratfink]

Well I've narrowed it down . I noticed that my driver and my big box don't like each other. Something is up in my driver box and I don't know what it is. Reflect jumps way high when the driver is inline with the big box, the driver looks good on a dummy load power/tune wise maybe it's getting rf and making the reflect high ?

 

[Ratfink]

No takers?

 

[Shockwave]

The bad news is one of the two amps is oscillating and creating RF output on other frequencies. That's why they typically show a good SWR on a dummy load that works at any frequency and a poor SWR into a tuned antenna that only matches the narrow frequency range being used. You'll need to test each one by itself into the antenna while checking the SWR. If they work good alone, the feedback causing the oscillation may be coming in through the DC wire if they are both on the same power supply. Try running the driver from a different power source to determine this. If that is the problem you may be able to make it work on the same power supply by placing ferrite chokes on the power wires.

 

[Ratfink]

The low power on the final amp was because of a 150 on the output of one of the 4 pill sections which I found by feeling the output combiner. They are both on different supply's and always have been.

 

[psycho]

Put it back to stock and see what happens. The tattletale resistors look good so the balance must be OK.

 

[Ratfink]

Put it back to stock and see what happens. The tattletale resistors look good so the balance must be OK.

Stock? Lol

 

[psycho]

Stock? Lol

Was the system working normal before the custom tuning you referred to? 100 watts average swing should get full advertised output from that amp.

 

[Ratfink]

Was the system working normal before the custom tuning you referred to? 100 watts average swing should get full advertised output from that amp.

Custom tuning? Wouldn't call it that. They system hasn't worked right since I got it . It has improved but still has little issues.