My cousin was asking me about this amp and I just don't know enough about them. Looks good to me but I hate to give bad info. any thoughts on these?
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Any Thoughts on the 757 amps?
- Thread starter Greg T
- Start date
It looks neatly done, but I'm no tech and am not sure about the transformers and stuff. My cousin has looked at many builders and has contacted a few, but everyone is months out. This guy posts them for sale on a regular basis so he was just wondering if anyone was familiar. Thanx for the input.
If you search “757 Boulder Built” he seems to have a Facebook profile. May be able to do so there.
Yes, he sells them on FB. I did have a chance to try the 4 pill. With just 100W drive it easily pushed the needle to 850w. He says you can safely put 150W drive into them for over 1KW out. The one I tested sounded good as well.
His name is Nick Stong
There are several builders that have gotten away from the regular web site and just have a facebook page. You might also check out Hopper built and Carl built amplifiers.
Thanks guys. I had kind of already figured out that he only did business through Facebook because I couldn’t find a website and he doesn’t allow comments on YouTube.
Unfortunately I don’t have a Facebook account.
Unfortunately I don’t have a Facebook account.
850 out of 4 2879s is going to be mostly garbage coming out, I can't imagine 1kw. 500W out of 4 2879s at 13.8V is a good honest number. Much more than that and you're spewing trash.
I used to think that, also. I grew up using tube stuff and slowly made the transition, unenthusiastically, to solid state. I remember 2 and 4 pill amps back in the day that sounded absolutely terrible while putting out 150 watts. Things are much different now and designs have drastically changed. I'm not a tech so I don't have the vocabulary to explain it, but the newer amps are able to hammer out huge power and remain acceptably clean.
As an example, I run a Texas Star DX-500V that came out of the box doing about 450 W PEP with a 35W drive. Now, this is what is expected of it. I did a simple power wire upgrade because of the instability in current draw and voltage drop. I removed the two fuse holders and ran separate 8ga power wires to each board. I now have two red and two black wires coming from the amp, terminated via Anderson Power pole. Now, with volts and drive the exact same as before, I'm getting a tad over 700W out of this amp with rave audio reviews and not one person complaining about dirt, distortion or splatter. Plus, I used to idle it at 14.5 volts, and it would drop to about 13.5v (roughly) during transmit. Now, it idles at 14.5v and drops to 14.2v under heavy load.
Back to 757, I have no idea how he gets a 4 pill to take 150W drive, let alone get 1KW out of it, but I know he's not the only one these days. The techs at Texas Star told me never to drive a 4 pill with more than 30W PEP, so that is what I do. Yet, I see BBI, Gatekeeper, Hopper, Donkey Stomper, and tons of others driving with 100W radios and pushing HUGE wattage. As I said, I can't explain it, but I know they're doing it, and doing it well. Some, better than others.
With enough swamping resistors on the input, you could drive a 1 pill with 5KW. You just burn off the excess power as heat and give the transistors what they're looking for. Waste of energy, especially in a mobile setup where you're limited by your alternator. No point in running a driver to get 150W to put into the 4 pill when you're going to burn off 3/4 of that as heat. A dual final radio would get you the same result. You could use the amps the driver is eating up to keep the 4 pill fed.
Same reason why 2x4 or even 1x4 amps are silly. A 1x4 made sense in "before times" when radios struggled to make an honest 4W, but these days, pretty much any radio made in the last 20 years, tuned up properly, can drive a straight 4 pill to saturation just fine. A 1x8 makes sense on a single final radio, but a tuned up dual final radio driving a straight 8 can make almost as much power. And in the end, the receiving station wouldn't be able to tell the difference in signal strength between the two anyway, maybe 850 vs 1000w. If you have a radio with a RFX75 or something similar, that will drive a straight 8 to saturation no problem.
There's no magic recipe for squeezing grossly more power out of a transistor and the signal remaining clean. You can maximize the clean power out with things like keeping the transistor fed with solid voltage (like you did by upgrading the power wires), or feeding them with higher voltage (like competition guys running a motor maul, though I hear the Toshiba clones don't like high voltage). But in the end, anything over ~125W output per Toshiba 2879 at 13.8V is mostly garbage, not on your fundamental frequency. These days, with the price of Toshibas, you're better off cruising them than burning them up...
The boulder built guy may make pretty looking amps, but he has no idea what he is doing.
Only someone who does not understand RF theory would make a video like this thinking he's showing how smart he is.
Exhibit A:
LC
Only someone who does not understand RF theory would make a video like this thinking he's showing how smart he is.
Exhibit A:
LC
That is because those amps are wide open with no filtering, so there are harmonics being generated, so think of the meter seeing transmissions from more than one transmitter at a time, so while you might not hear the splatter, they are FOR SURE generating harmonics/RF junk/spurs elsewhere.
Moral of the story is, if it sounds too good to be true, it is.
A side question: not sure sbout pills inside but I am getting a RCI2970N3 soon and after properly being peaked it is supposed to do over 300 watts. Anyone know what size power supply I will need for this radio.