TNT-1500 problems

[DD2ML]

Hi and sorry for my bad english. I´m from Germany and bought a TNT-1500 from X-force. I wanted to run it on 10m. When It was shipped I hooked up and there was no output and the input vswr was very high. I looked inside and was very shocked about the input circuit. There where some caps in line with the input and the ptt relay was not able to short the input/output cause the cables where not right on there.
I took the circuit from a sweet 16 and rebuild it like that. The only difference are the resistors for the bias which are not 25Ohms, they are 10Ohms, so have more bias current. It´s about 500mA per TR.
I cut of and throw away the ssb delay circuit and the hf-vox. This are things you never need in a HF amp. I built in a cinch to key it direct from the radio.

My problem is now when keying the amp with 40W it produces about 400-500W output, but the input current is at 150A. That is 1800W input. There must be something wrong. This would be a efficiency abt. 30%.
What can be wrong?

Here´s a pic from inside:
http://www.bluelincoln.de/bilder/pa/tnt.jpg

 

[9C1Driver]

When you first got it and it did not work I would have called X-Force right away. Now that you modded it yourself all bets are off for warranty work. Did you discuss your plans with them before you bought it? You might have been better off with an Ameritron for what you want to do. You might see if Peakaboo can give you some pointers, he's a sharp dude and could probably figure it out.

 

[Bionic Chicken]

I can't see it all the way but something looks like it might not be right on the relay wiring. From the photo it looks like the jumper for bypass operation is grounded. This would keep a radio from transmitting through the amp when in standby.
Maybe I am missing something?

 

[DD2ML]

I wrote an email to carl and he said that this thing would work but it dosn´t.
He has no shematics or wan´t give it to me. I had not the time to send it back to US cause want to run it on a contest on 10th of January.
I did the relay wiring like it is in the dx-1600 shematic so I think it´s ok.
It works and puts out abt 800W with 100W of drive but the current is much to high. The gain is also not as specific of the TR´s. It should be 13db but is less than 10db.

 

[Shockwave]

I wrote an email to carl and he said that this thing would work but it dosn´t.
He has no shematics or wan´t give it to me. I had not the time to send it back to US cause want to run it on a contest on 10th of January.
I did the relay wiring like it is in the dx-1600 shematic so I think it´s ok.
It works and puts out abt 800W with 100W of drive but the current is much to high. The gain is also not as specific of the TR´s. It should be 13db but is less than 10db.

From a quick look at your picture it would appear the input drive for the RF keying circuit has been connected to the output connector of this amp. If you're able to get the amp to key, the RF sensing circuit would be loading the output and could account for the low gain and high current.

 

[DD2ML]

I don´t understand correctly, but I think you mean that the input and output is exchanged. That might be impossible because the high voltage C is only in the ooutput but maybe I´m wrong.
Here are some more puctures:

http://www.bluelincoln.de/bilder/pa/xforce/1.JPG
http://www.bluelincoln.de/bilder/pa/xforce/2.JPG
http://www.bluelincoln.de/bilder/pa/xforce/3.JPG
http://www.bluelincoln.de/bilder/pa/xforce/4.JPG
http://www.bluelincoln.de/bilder/pa/xforce/5.JPG
http://www.bluelincoln.de/bilder/pa/xforce/6.JPG

 

[Shockwave]

I don´t understand correctly, but I think you mean that the input and output is exchanged. That might be impossible because the high voltage C is only in the ooutput but maybe I´m wrong.
Here are some more puctures:

http://www.bluelincoln.de/bilder/pa/xforce/1.JPG
http://www.bluelincoln.de/bilder/pa/xforce/2.JPG
http://www.bluelincoln.de/bilder/pa/xforce/3.JPG
http://www.bluelincoln.de/bilder/pa/xforce/4.JPG
http://www.bluelincoln.de/bilder/pa/xforce/5.JPG
http://www.bluelincoln.de/bilder/pa/xforce/6.JPG

On the right hand side of the big relay you have two purple wires connected on the 3rd terminal down from the top. The purple wire that goes to the capacitors and diode on top of the big relay looks wrong to me. It looks like this is part of the old RF keying circuit and is loading the output of this amp. I would disconnect that one purple wire and see how the amp performs.

 

[DIRTYWHITEBOY]

10db gain and very high current draw is fairly usual for that style ampifier on 13.8v even in class c, they are designed to run on 20+volts on cb keydowns, adding the shitty biasing circuit they use causes them to become less efficient and a poor impedance match,
der Verstärker ist richtig nicht für Betrieb 13.8v bestimmt,
das ist hässlich.
Karl kopierte den Entwurf, er versteht nicht, wie sie funktionieren

op:

 

[DD2ML]

@Shockwave
The purple cable you mean is on the lowest port which is B+ from power switch.

@Dirtywhiteboy
If you look in the datasheet of the 2879 you see that it´s characteristical dates are given with 12,5V on 28Mhz and then the gain should be a min. of 13db and typical 15,2db. Ok some losses on the shemtaic could be but not so much.
It works in Class B I think. Class C is without bias current or am I wrong?
There must be another problem.
You are right, I beleave Carl has no idea what´s going on in these amps. He just build this stuff but doesn´t really now what it is :headbang

 

[earthquake]

just a few comments! only 10 amp relay in a 8 transistor amp??? and wheres the diode on the relay?!! sorry if ive stated the obvious but had to say something!!! 73s.

 

[Shockwave]

@Shockwave
The purple cable you mean is on the lowest port which is B+ from power switch.

@Dirtywhiteboy
If you look in the datasheet of the 2879 you see that it´s characteristical dates are given with 12,5V on 28Mhz and then the gain should be a min. of 13db and typical 15,2db. Ok some losses on the shemtaic could be but not so much.
It works in Class B I think. Class C is without bias current or am I wrong?
There must be another problem.
You are right, I beleave Carl has no idea what´s going on in these amps. He just build this stuff but doesn´t really now what it is :headbang

No, that's the blue wire on the lowest terminal. The purple wire I am talking about is one up from the lowest and has two wires on it. The purple wire that goes to the keying circuit on the top of the relay is the problem. It connects to the cathode of the diode and the base of the keying transistor. It has been incorrectly connected to the RF output terminal.

 

[DD2ML]

No, that only looks like in the pics but its soldered to the lowest pin on the blue wire. The RF output is alone.

 

[bob85]

OHMY:w00t:
dwb actually learned something usefull from paltalk and biasing experiments,
give that man a gold star

 

[grimace]

that 100ohm looks a little brown

 

[DD2ML]

This 100Ohm is grey. I had to change it. The old one was smoking a little bit. Perhaps the combiners are also not exact on impedance?