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Donkey Stomper 2x8 pictures and discussion
- Thread starter loosecannon
- Start date
Memorable line from Deep Space Nine:
"I believe in coincidence. I just don't trust coincidence".
73
"I believe in coincidence. I just don't trust coincidence".
73
the amp is all fixed and back to its owner.
first of all, a big thanks to Nomad for pointing out those .01uF caps in the negative feedback circuits. i don't think i would have caught that had you not noticed it.
looking at those amp plans everyone copies, yep, they call out .01uF also.
no wonder.
changed them all out to .1uf, raised the input tuning transformers up off the board (whether or not it helped i dont know but it was bugging me), and added a variable tuning cap for the input.
they had 180pf on there, and i found that 100 to 110 was plenty.
re-adjusted the trombone cap as well, and got decent input and output readings on a real antenna.
i found the fans to be a great help when tuning LOL!
when the fans slow down your tune is out of town LOL.
thanks to all who followed the thread.
i still have to say though that these amps are not a good design.
yes, i made it work, but it still puts out less power above channel 40 then it does below channel 1.
seems like these amps are specifically designed to work from channel 6 up to channel 28 and nowhere beyond those limits LOL.
neither the owner nor I was interested in experimenting further with it.
he just wanted it to work and now it does.
he noted that the performance was better in his mobile than it was at my base station.
LC
first of all, a big thanks to Nomad for pointing out those .01uF caps in the negative feedback circuits. i don't think i would have caught that had you not noticed it.
looking at those amp plans everyone copies, yep, they call out .01uF also.
no wonder.
changed them all out to .1uf, raised the input tuning transformers up off the board (whether or not it helped i dont know but it was bugging me), and added a variable tuning cap for the input.
they had 180pf on there, and i found that 100 to 110 was plenty.
re-adjusted the trombone cap as well, and got decent input and output readings on a real antenna.
i found the fans to be a great help when tuning LOL!
when the fans slow down your tune is out of town LOL.
thanks to all who followed the thread.
i still have to say though that these amps are not a good design.
yes, i made it work, but it still puts out less power above channel 40 then it does below channel 1.
seems like these amps are specifically designed to work from channel 6 up to channel 28 and nowhere beyond those limits LOL.
neither the owner nor I was interested in experimenting further with it.
he just wanted it to work and now it does.
he noted that the performance was better in his mobile than it was at my base station.
LC
turborich,
I can understand the logic behind sending a faulty product back to it's manufacturer and getting a warrantied repair or a replacement, but i don't believe that would have been the correct move here.
first, the guy is local to me, which means he doesn't have to pay shipping either way.
second, the product was assembled by the same person who tunes them, and that person didn't do a very good job of that the first time, so why would one assume he would do better the second time.
chad can follow the instructions to assemble an amp, but i don't think he understands the concepts behind amplifiers too well.
who knows, this could have been an early amp and he has gotten better after being taught how to tune them, but in this case, the guy just had more confidence in me than in him.
LC
I can understand the logic behind sending a faulty product back to it's manufacturer and getting a warrantied repair or a replacement, but i don't believe that would have been the correct move here.
first, the guy is local to me, which means he doesn't have to pay shipping either way.
second, the product was assembled by the same person who tunes them, and that person didn't do a very good job of that the first time, so why would one assume he would do better the second time.
chad can follow the instructions to assemble an amp, but i don't think he understands the concepts behind amplifiers too well.
who knows, this could have been an early amp and he has gotten better after being taught how to tune them, but in this case, the guy just had more confidence in me than in him.
LC
i don't know who that is selling the Donkeys now with the crazy high price or best offer. heck, just price the thing right.
Tried calling Mr Stomper couple or three weeks ago about buying one and he didn't get back to me.
He has usually returned call.
Tried calling Mr Stomper couple or three weeks ago about buying one and he didn't get back to me.
He has usually returned call.
Frankly, there are just too many little errors in this build to trust that the builder is even aware of them. The soldering makes me question both the skills and his understanding of the circuit. Look at this current eBay auction here: https://www.ebay.com/itm/BRAND-NEW-...988237?hash=item288231b7cd:g:ERkAAOSwblldQhg8
Check out the solder around each of the transistors emitter connections. It's almost as though the goal was to simply bond all of these gold plated tabs together rather than to bond them all to the PC boards copper ground plane. Several look like there may be no solder flow under the tabs at all. The soldering iron used, appears only hot enough to heat the transistors and not the copper board below.
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CJ or Mr Stomper said he isn't building boxes anymore so maybe that's why some of that solder work is questionable.
What he's doing there is covered in the owners manual for a MFJ antenna analyzer. You can download a copy from their website.
When using crude transistor amps that are ran well past safe limits and radios with cheap mosfet finals ran beyond safe limits some of this voodoo can help keep the smoke in. Been there.
What he left out was "The line must be open circuited at the far end for odd multiples of 1/4 wave stubs (i.e. 1/4, 3/4, 1-1/4, etc.) and short circuited for all half-wave stub multiples (like 1/2, 1, 1-1/2, etc.)"....quoted from the mfj 259 manual.
Where he's dead wrong is jumper lengths changing swr readings on a dummy load. Something is wrong with his dummy load or the coax. When the load matches the impedance of the feedline and there is no reactance it doesn't matter how long the cable is.
X2 on soldering the shield. I've known guys that were set against it. I went to crimp connectors for anything bigger than rg8x. There's a fine line between hot enough to solder the shield and melting the dielectric.
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i like the crimp tool for Times coaxial as well. consistent and like you said a fine line with the soldier
I think he found a new way to tune a 16 pill. wrap a half wave of coax around each combiner.
but really is this standard or something new ?
I haven't seen this before
but really is this standard or something new ?
I haven't seen this before
First. Those HG2879’s don’t Tune like Toshiba. So I’m sure the wrong caps across input transformers. Across the output should be 1000pf. The input and output are different not to mention he used longer “comp” transformers. So I’m sure the 4 transistor sections are way off.